Southwest Research-Extension Center, Field Day 1992

This report is brought to you for free and open access by New Prairie Press. It has been accepted for inclusion in Kansas Agricultural Experiment Station Research Reports by an authorized administrator of New Prairie Press. Copyright 1992 the Author(s).


WEATHER INFORMATION AT GARDEN CITY by William Spurgeon and Charles Norwood
Climatic conditions were very favorable for crop growth in 1991, particularly for summer row crops. Above normal rainfall in May and timely rainfall in June, coupled with above normal rainfall in August, produced an excellent corn crop.
Precipitation totaled 20.72 inches or 2.86 inches above normal. Snowfall was above normal, with 7 inches in March and 17 inches in late October and early November. Three inches fell in January and only three tenths of an inch in February.
Temperatures were warmer than normal for most of the year except during the summer and the first part of November. Near normal to slightly cooler temperatures in July and August helped provide adequate energy for the crops without causing extreme stress. Only one record high temperature occurred (93° on October 18); however, six record lows occurred. The high for the year was 101° on July 8 and August 1. There were 4 days of 100° or higher temperatures. Three below 0° readings occurred, all of which were record lows. They were -8°, -5°, and -1° and occurred on January 1, November 3, and November 4, respectively.
Average wind speed was 5.1 mph or 1.0 mph below normal. However, extremely strong winds occurred twice in the spring, causing extensive damage to small structures and sand pitting of vehicles. Open pan evaporation was 71.01 inches or 7.31 inches below normal. The frost-free period was from May 6 through October 24, or 172 days, 2 days above normal.
A complete summary of the weather is presented in the accompanying greatest in February, when the 40.2 0 average temperature was 6.1 0 above normal. The highest temperature was 105 0 on July 7, and a total of 8 days had of 100 0 or higher. The lowest temperature was -4 0 on November 3, which was the earliest subzero temperature ever recorded at the station by one full week. The -2 0 reading on January 30 was the only other day of sub-zero temperature for the year. The last frost (30 0 ) in the spring was on May 1 (28 0 ), which was the normal date, and the first frost in the fall was on October 5 (25 0 ), which was 2 days earlier than normal. There were 157 frost-free days, 2 days less than the normal.
Open pan evaporation from April through September totaled 75.46 inches, which was 3.78 inches above the normal of 71.68 inches. Wind speed for the same period averaged 5.4 mph compared to the normal of 5.6 mph.
Precipitation for 1991 totaled 20.65 inches or 4.74 inches above normal. Precipitation was above normal in 6 months. The wettest were June, July, and August with 4.31, 3.49, and 4.95 inches, respectively. The largest single amount of rainfall was 2.66 inches on August 3. March, November, and December were also above normal. The remainder of the year had below normal precipitation, including February, which was one of the driest on record with only a trace reported the entire month. Snowfall for the year totaled 28.1 inches, and the largest single amount, 6.0 inches, fell on March 17.
The air temperature was above normal for 3 months of the year and below normal the rest of the year. The warmest month was July, with an average temperature of 75.8 0 and an average high temperature of 90.7 0 . The coldest month was January, with an average temperature of 25.4 0 and an average low of 13.7 0 . Deviation from the normal was 3 Preemergent herbicides (usually 3 lbs Ramrod + 1.0 lb atrazine) were used in the WSF-CT and SF treatments for sorghum. Reduced and NT sorghum usually received 4 lbs Ramrod preemergence. In years of light weed pressure, preemergent herbicides probably were not needed in the RT and NT plots.

SUMMARY
Increases in available soil water and yield from a reduction in tillage occurred more often in the WSF system than in the WF system and more often for sorghum than for wheat. Yields with reduced or no tillage were higher in 2 of 5 years for wheat in WSF INTRODUCTION A long-term study is being conducted to determine the effects of cropping system and reduced or no tillage on dryland winter wheat and grain sorghum. The effects of reduced and no tillage on available soil water and yield are being determined. This report is a summary of the data collected from 1987 through 1991.

PROCEDURES
The wheat-fallow (WF), wheat-sorghum-fallow (WSF), sorghum-fallow (SF), continuous sorghum (SS), and continuous wheat (WW) systems were studied. Herbicides were used in place of some or all tillage. Treatments varied somewhat from year to year, but the following are currently in use. Wheat was planted with a John Deere HZ drill in 16-inch rows at a rate of 40 lbs/A. Sorghum was planted with a Buffalo slot planter in 30-inch rows at a rate to result in 25,000 plants per acre. Available soil water was measured at 1-foot intervals to a depth of 5 feet at the end of fallow. Grain was harvested with a plot combine, and grain yields were reported at 12.5% moisture. The soil type was a Richfield silt loam with a pH of 7.8, organic matter content of 1.5%, and an available water holding capacity of 10.8 inches in a 5-foot profile. The experimental design was a randomized complete block with three replications.

RESULTS AND DISCUSSION
The use of atrazine in the WF and WSF system (WF-RT and WSF-RT) typically resulted in the elimination of two tillage operations, the one following harvest and the first operation in the following spring (Table 1). Atrazine, particularly at the 1.0 lb rate in WF-RT sometimes did not result in adequate volunteer control, making tillage or the use of postemergent herbicides necessary. The use of Bladex (following atrazine) in the WF system (WF-MT) resulted in the elimination of more than half of the tillage, whereas the use of Bladex prior to sorghum (WSF-NT) eliminated all tillage. Two tillage operations were typically eliminated when Bladex was used in the WSF system prior to wheat (WSF-RT). There were no SS-CT plots, but this treatment would require spring tillage similar to WSF-CT. Reduced or no till in the SF system is not practical, because of the long fallow period and is not currently being studied.

Soil Water
The amount of available soil water (hereafter referred to as soil water) at wheat planting is presented in Table 2. The amount differed between tillage treatments in the WF system only in 1990. In the WSF system, the NT plots had more soil water only in 1989. The WF-CT and NT plots had more soil water than WSF-CT and NT in 1989, also. The advantage for WF in 1989 occurred because of the longer fallow period; much of the storage occurred early in fallow, before the beginning of the WSF fallow period. The WW treatment had less soil water than all WF and WSF treatments in 1987 and 1990; however, the amount did not differ from that in either WSF treatment in 1988 or WSF-CT in 1989.
The amount of soil water at sorghum planting is presented in Table 3. In the WSF system, more soil water was present in RT and NT than in CT in 1987, 1988, 1989in 1990, the amount in NT, but not RT, exceeded that in CT. No significant differences occurred in WSF in 1991. No significant differences occurred between RT and NT in any year. Soil water in SS was less than that in all WSF treatments in 1988WSF treatments in , 1990WSF treatments in , and 1991, but more than in WSF-CT in 1987 and1989. The longer fallow period of SF resulted in more soil water than in WSF-RT in 1991 and more soil water than in WSF-CT in 1987, 1989, and 1991

5
Wheat Yield Wheat yields are presented in Table 4. Tillage caused no difference in yield in the SF system. In the WSF system, RT and NT yielded more than CT in 1989, and NT yielded more than CT in 1991. Although an increase in soil water caused the increase in 1989, there was no difference in soil water in 1991 (Table 2). A yield reduction occurred in WSF-NT in 1990, because extremely cold temperature in December 1989 caused some tillers to abort. The NT plants were exposed more to the cold because of shallower planting. Under the same conditions, the yield of WF-NT was not reduced, because it was insulated from the cold by the wheat straw remaining from the previous crop.
A comparison of the WF and WSF systems indicates that their yields were similar, except in 1989, when more soil water at planting resulted in higher WF yields. The yield of WW was substantially less than those of either WF or WSF in 1987, 1989, and 1991. In 1988, WW yields were similar to those of WF and WSF, but all yields were low. Above average rainfall in 1990 resulted in high yields from all systems.  Avg. 6.9 8.3 8.6 6.7 8.5 __________________________________________________________________ 1 Means within a row followed by the same letter do not differ (P<0.05).

6
Grain Sorghum Yield Grain sorghum yields are presented in Table 5. The yield of WSF-NT and RT exceeded that of WSF-CT in 4 of 5 years. The yield of WSF-NT exceeded that of WSF-RT in 2 of 5 years. Continuous sorghum and SF yield could not be statistically compared with WSF yields because of bird damage in 1988. However, SS yields were generally lower than WSF yields, whereas SF and WSF yields were similar.

SUMMARY
A comparison of dryland WSF and WCF cropping systems with similar systems receiving a single irrigation indicate that substantial yield increases can occur in the irrigated systems. However, timely rains can result in dryland yields as high as irrigated yields. Consistent yield increases from irrigation occurred in 1 of 2 years for wheat and 1 of 3 years for sorghum and corn. More data are needed before conclusions can be made regarding the feasibility of these very limited irrigated systems in comparison to dryland.

INTRODUCTION
Because of declining water tables and increasing energy costs, many farmers can no longer afford to use full irrigation. They have been forced to reduce irrigation and some have converted irrigated acres to dryland. This study was designed to evaluate very limited irrigation, compared to dryland, with the objective of slowing the conversion of irrigated acres to dryland. Moisture conserving practices, such as no-till, are incorporated into the study.

PROCEDURES
The study is basically a comparison of the dryland wheat -sorghum or corn-fallow (WSF, WCF, or WS(C)F) system with WS(C)F systems in which the wheat, sorghum, or corn or both crops are flood irrigated. An irrigated wheat-fallow-dryland wheatcontinuously irrigated wheat (alternate irrigateddryland, or AID) system is included. Both the AID and WS (C) F systems allow two crops in 3 years. Also included are irrigated continuous wheat (IWW), corn (ICC), and sorghum (ISS) and dryland continuous sorghum (DSS) and wheat (DWW). The irrigated crops receive a single 6-inch irrigation. The wheat is irrigated at joint stage, the sorghum at boot stage, and the corn at tassel stage. In addition to the inseason irrigation, the irrigated continuous crops receive a 6-inch preirrigation. Water stored during fallow substitutes for the preirrigation for crops planted following fallow. The specific crop sequences are given in the tables.
The experimental design is a randomized complete block with four replications. The corn and sorghum are planted no-till into wheat stubble remaining from the previous crop. Atrazine, at a rate of 2 lb/A, is applied following wheat harvest; this is followed by 1.6 lb/A cyanazine applied 15 to 30 days preplant to the row crops in the spring. The irrigated wheat stubble in the AID system receives 1 lb/A atrazine after harvest, followed by tillage as needed. Tillage is performed as needed prior to wheat in the WCF, WSF, IWW, and DWW systems and for DSS, ISS, and ICC. The soil type is a Richfield silt loam with a pH of 7.5 and an organic matter content of 1.5%.

Wheat Yield
Wheat yield data are presented in Table 1. Rainfall well above normal and ideal conditions during grain fill produced very high (also unrealistic) wheat yields in 1990. Irrigation did not significantly improve wheat yields. The situation was more normal in 1991, with yields ranging from 23 bu/A for DWW to 71 bu/A for irrigated wheat in the WSF and WCF systems. The single irrigation resulted in a 21 bu/A yield increase when comparing the dryland and irrigated WS(C)F systems. Irrigating both crops did not improve wheat yields over those obtained when only the wheat was irrigated. The irrigated yield from the AID system was similar to that of irrigated wheat in the WS(C)F system. Continuously irrigated wheat yielded less than the irrigated wheat in the WS(C)F systems and did not differ significantly from dryland wheat.

Sorghum Yield
Grain sorghum was generally unaffected by cropping system or irrigation in 1989 and 1990, because of timely rains (Table 2). Rainfall was below normal in 1991, resulting in irrigated WSF yields nearly 60 bu/A higher than dryland WSF yields. Dryland sorghum following irrigated wheat yielded 61 bu/A, Means within a column followed by the same letter do not differ (P< 0.05).

_____________________________________________
Cropping System 1989System 1990System 1991 Avg.  (Table 3) were higher than sorghum yields. Because of rainfall, irrigated corn did not consistently yield more than dryland corn in 1989. In 1990 also no differences in yield occurred except that ICC yielded less than the other systems. This occurred in 1989 also, indicating that corn grown in rotation can yield more than continuous corn. (This isn't anything new, but the differences in 1989 and 1990 were substantial.) In 1991, yields of the irrigated treatments exceeded those of dryland by more than 50 bu/A. As with sorghum, dryland corn following irrigated wheat yielded substantially more than corn in the all dryland system, indicating carryover soil water.

LATE-PLANTED WINTER WHEAT by Merle Witt
Winter wheat in the Great Plains is not always planted at the optimum time for a variety of reasons. Sometimes replanting is necessary following stand loss to wind, pests, or winter killing. In other cases, the seedbed may be too dry or too wet to plant at a normal time. Additionally, planting may be purposely delayed in order to avoid diseases or insects, to pre-irrigate, or to accommodate a double-cropping sequence. In order to identify wheat responses to delayed establishment, sequential monthly planting dates from 1 October to 1 April were used during the 7 years from 1985-1991 at Garden City, Kansas. TAM 107 was seeded at a constant heavy rate in bordered drill strip plots in RCB design. Resulting relative grain yields tapered off with progressive planting dates as follows: 1 October = 100%, 1 November = 77%, 1 December = 59%, 1 January = 57%, 1 February = 41%, 1 March = 16%, 1 April = 0%.
Wheat planted on April 1 did not vernalize or reproduce. Relative to wheat planted on the optimum date, 1 October, that planted on 1 March was the last to produce heads and grain but was the lowest yielding; gave the most delay in heading (26 days later); was the latest to ripen (17 days later), and the shortest statured (5" less); produced the smallest seed (43% less weight), the lowest test weight (21% less), the fewest heads/plant (58% fewer), the fewest kernels/head (33% fewer), and the fewest number of kernels per plant (73% fewer); and had the shortest grain filling period (9 fewer days). Little variation occurred through the range of dates for stand emergence or number of spikelets/spike. These results can assist farmers, seed sellers, crop insurers, and administrators of Farm Programs to make cropping decisions on "how late is too late" for planting winter wheat in the Central Great Plains. Soybeans were seeded on May 5, 1989; on May 2, 1990; and May 29, 1991. Plots were grown on a Keith silt loam soil in all 3 years, with Treflan at 2 pints per acre incorporated for weed control. In each of the 3 years, the soybeans followed a year of summer fallow preceded by a crop of grain sorghum. Grain yields are displayed in Table 1.
Days from planting to maturity of the four maturity groups (varieties) as an average over three planting rates and over 3 years were MG I (Weber 84), 104 days; MG II (Ohlde 2193), 112 days; MG III (Resnik), 120 days; and MG IV (Sparks), 124 days.

SHORT-SEASON CORN HYBRIDS by Alan Schlegel and Merle Witt
A test of short-season corn hybrids was conducted at two western Kansas locations. No entry fee was charged nor was an attempt made to solicit the broad range of entries that are available. This test was initiated to quickly evaluate the suitability of a few short-season hybrids to our environment, as well as to consider appropriate plant population levels suitable to produce high grain yields from these dwarfed plant types. Higher plant populations than used for full-season corn hybrids were found to be appropriate for top grain yields. Earlyseason corn data for Tribune and Garden City are shown in Tables 1 and 2 Pre-plant plus 20"

SUMMARY
The objective of this study was to evaluate soybean inoculants. A new material, "HiStick", a very sticky adhering product from Agricultural Genetics Company, was to be tested for improved performance in attaching to seeds and providing Rhizobium bacteria for symbiotic nitrogen fixation.

PROCEDURE
This study was conducted on a soil mapped as Ulysses silt loam. The field had previously been in corn for 2 years (1990 and 1989) and grain sorghum (1988). Soybeans (Ohlde 3431) were inoculated and planted on 29 May 1991. Extreme care was taken to prevent cross contamination of the inoculants during planting. The dry seeds were mixed at the recommended rate of 1 pack (250 g) of HiStick per 3 bushels of seed. "Nitragin" soybean inoculant was also applied at the recommended rate. Control, noninoculated, soybeans were also included in the study. The soybeans were harvested on 15 October, 1991 from a harvest area of 5 by 100 ft. Plant color and nodulation ratings were determined on 30 July 1991 near mid-flower. The nodulation rating was based on a scale of 10, with 0 being no nodulation and 10 being effective nodulation.

RESULTS
Plant color ratings at mid-flower showed no difference between the treatments. Nodulation ratings showed "HiStick" to have the best nodulation. The noninoculated control had no nodules present at midflower. The "Nitragin" inoculant had an average rating of 4.25, with high variability. The "HiStick" had a rating of 7.5. Greater nodule weight per plant was also observed with the "HiStick" inoculant.
Grain yields and test weights are summarized in Table 1. There was no significant difference in test weights between the treatments. Grain yields were significantly improved by inoculation with "HiStick"and were greater than those of either the control or the other inoculation.
Plots were established to estimate disease losses and evaluate commercial fungicides. Seed of two varieties (TAM 107 and Thunderbird) were planted at 75 lb/A on 25 Sept. 90. Plots were flood irrigated with approximately 4 in of water on 27 Mar and 15 May. Two commercial fungicides were compared to an unsprayed control and a disease-free control (two applications of Folicur). On 26 Apr. (growth stage Feekes 8 (flag leaf just visible)) and 8 May (Feekes 10 (boot)), fungicides plus 0.25% (v/v) X-77 spray adjuvant were applied in water at 20 gal/A. Disease ratings for percent of flag leaf covered by leaf rust were made on 4 June. Plots were harvested on 20 June.
Leaf rust was undetectable in plots on 8 May. However, leaf rust was severe on TAM 107 and moderate on Thunderbird on 4 June. Apparently, large amounts of inoculum were transported into the area in mid-to late May. The Bayleton plus Dithane M-45 tank mix was more effective in controlling leaf rust than Tilt, probably because the Tilt was partially exhausted by the time inoculum arrived. However, this difference was not reflected in yield differences between the two treatments. Using the unsprayed control and the disease-free control, the estimated yield loss was 21.8 bu/A (23%) for TAM 107 and 5.4 bu/A (7%) for Thunderbird. The two available commercial fungicide treatments recovered all the yield loss for Thunderbird and about half of the estimated loss for TAM 107. At prevailing local prices, either commercial fungicide would have been a profitable investment for irrigated wheat in western Kansas in 1991. However, severe leaf rust epidemics do not occur regularly enough in western Kansas to justify routine fungicide applications ( Table 1).
Assuming a total expense of $15.00 per acre for fungicide plus application costs, and a wheat price of $3.50 per bushel, the Tilt treatment would have returned 330% and the Bayleton/Dithane treatment would have returned 318% on the investment for TAM 107. For Thunderbird, the Tilt treatment would have returned 139% and the Bayleton treatment would have returned 153% on the investment. This analysis is extremely dependent on wheat price. Folicur is not commercially available, so return on investment cannot be calculated.
Using the Folicur treatment as the standard, the TAM 107 experienced 21.8 bu/A (23%) yield loss primarily from leaf rust. The Thunderbird experienced 5.4% bu/A (7%) yield loss.

THIRTY YEARS OF NITROGEN AND PHOSPHORUS FERTILIZATION OF IRRIGATED CORN AND GRAIN SORGHUM
by Alan Schlegel and Kevin Dhuyvetter SUMMARY Grain yields of irrigated corn and grain sorghum are increased by N and P applications. The economic optimal N rate is about 155/acre for irrigated corn and about 135 lb/acre for irrigated sorghum. The optimal N rate is fairly constant across yield potential. The addition of fertilizer P at 40 lb P 2 O 5 /acre is sufficient to maintain soil P levels for sorghum, but a higher rate is needed for corn. Nitrate accumulation in the soil profile is greater with sorghum than corn at equal N rates, reflecting the greater yield and N removal by corn. Application of P with N decreased nitrate accumulation, emphasizing the importance of a balanced fertility program. Application of N in excess of that needed for crop growth reduced net income and increased nitrate accumulation and leaching below the active crop root zone.

INTRODUCTION
Nitrogen (N) and phosphorus (P) fertilizers were applied for 30 years to irrigated continuous corn and grain sorghum at Tribune, KS. The objectives of the study were to evaluate the effect of long-term fertilization on grain production, soil chemical properties, and production economics.

PROCEDURES
Nitrogen and P fertilizers have been applied annually since 1961 to irrigated corn and grain sorghum grown on a Ulysses silt loam. Initial chemical properties of the surface soil (0-6 inch) were 17 ppm P (Bray-1), 1.4% organic matter, and pH of 7.9. Fertilizer treatments included N rates ranging from 0 to 200 lb N/acre in 40 lb increments with and without P at 40 lb P 2 O 5 /acre. Grain yield was adjusted to 15.5% moisture for corn and 12.5% for grain sorghum. Periodically during the study, surface soil samples (0-6 inch) were collected and analyzed for Bray-1 P. After harvest in 1990, soil samples to a depth of 10 ft. were collected and analyzed for NO 3 -N.
Economic analyses were based on estimated yield response curves to determine net revenue, cost of production per bushel, and optimal economic N rate for corn and sorghum. The P rate for all analyses was 40 lb P 2 O 5 /acre. Because yields varied from year to year, the dataset was also partitioned by yield potential (low, medium, and high) based on annual average yields. Optimal economic N rates were determined for each yield potential. The cost/ price assumptions used were N cost of $0.15/lb, corn price of $2.50/bu, sorghum price of $2.25/bu, fixed cost for corn of $200/acre, and fixed cost for sorghum of $120/acre. The fixed costs included all production expenses other than N cost.

RESULTS AND DISCUSSION
Corn yields averaged over 31 years were increased by N rates up to 160 lb N/acre (Table 1). Although no yield response to P was observed during the first 5 years of the study, since then the yield response to P has steadily increased. Phosphorus fertilizer, across all N rates, increased corn yields 24 bu/acre over 31 years, 37 bu/acre over the past 10 years, and 73 bu/acre in 1991. When P was applied with adequate N in 1991, corn yields were over 100 bu/acre greater.
Sorghum yields increased with increased N rates, particularly with the first increment of N. Similar to corn, sorghum yield response to P fertilizer was first observed after about 5 years and has steadily increased since then. When averaged across N rates, P increased sorghum yields 12 bu/acre over 31 years, 18 bu/acre over the past 10 years, and 24 bu/acre in 1991. For both corn and sorghum, P applied without N did not increase grain yield. The yield potential of sorghum was about 25% less than corn.
When no fertilizer P was applied, soil P levels reduced rapidly from about 18 ppm Bray-1 P initially to less than 10 ppm after about 5 years and then stabilized at this lower level for both corn and sorghum (Figs. 1 and 2). At low N rates, soil P was increased by application of P fertilizer to both corn and sorghum. However, at higher N rates on sor-

Rate
Sorghum Corn N P 2 O 5 1991 1982-1961-1991 1982-1961-1991 1991 1991 1991 lb/acre -----------bu/acre l -----------   ghum, application of P (40 lb P 2 O 5 /acre ) only maintained soil P levels, indicating P removal was about equal to P additions. With corn, soil P levels tended to decline slightly even with application of P, indicating that P removal by corn exceeded that supplied by fertilizer P. Nitrate levels in the soil profile after 30 years of N and P applications were greater with higher N rates ( Fig. 3 and 4). At higher N rates, nitrate accumulation was less with corn than sorghum, reflecting greater N removal by corn. The addition of P reduced nitrate accumulation throughout the profile, particularly for sorghum. When high rates of N ( 160 lb/acre or above) were applied without P to sorghum, over 400 lb nitrate-Naccumulated in the soil profile between 5 and 10 ft., which is below most root growth. With reduced possibility of plant uptake, this nitrate is more susceptible to further leaching and could contaminate groundwater. This emphasizes the importance of a balanced fertility program and the environmental hazard of applying N fertilizer in excess of crop requirements.  The economic optimal N rate for corn is about 155 lb N/acre using the long-term average yield (Fig. 5).

Figure 5. Estimated yield response, net revenue, and cost per bushel of irrigated corn averaged over 30 years, Tribune, KS.
This is about 10 lb N/acre less than the N rate producing maximum grain yield and 10 lb N/acre more than that producing least cost per bushel production. When production functions were determined by yield potential, the economic optimal N rate remained at about 155 lb N/acre for years with low, medium, or high yield levels ( Fig. 6). For sorghum, the economic optimal N rate is about 135 lb N/acre based on long-term average yields (Fig. 7). This suggests that, for a particular field, the optimum N rate is fairly constant. Therefore, the practice of applying additional N to provide adequate N in case of better than average growing conditions, so called "insurance" N, is unnecessary and reduces net return. This compares to maximum grain yield obtained at 150 lb N/acre and least cost per bushel production obtained at 120 lb N/acre. The economic optimal N rate for sorghum at medium and high yield potentials remain about 135 lb N/acre, where as that for low yield potential is about 120 lb N/acre (Fig. 8).

CORN BORER MOTH FLIGHTS IN FINNEY COUNTY, KANSAS, 1991 by L. G. Wildman and Gary Dick
Corn borer moth flights at the Southwest Research-Experiment Station were monitored with a black light trap to give an indication of when fields should be scouted for corn borer second generation egg laying and larvae. European corn borer (ECB), Ostrinia nubilalis (Hubner), and Southwestern corn borer (SWCB), Diatraea grandiosella (Dyar), were monitored from May 4 to August 30, 1991.
The first generation of ECB reached a peak of 18 moths per night on May 5 and 6 ( Fig. 1). The second generation moths were numerous, peaking on July 19 at 156 (132 females and 24 males). The incidence of SWCB moths was very low. Only four SWCB moths were found in the light trap for the entire monitoring time.
The European Corn Borer Software, developed by the KSU Department of Entomology, was used to predict the peak second generation egg laying period. The peak egg laying period was between July 16-Aug. 3 (--**--, Fig. 1). The 25-50% oviposition period, July 20-26, is indicated by asterisks (***). Spider mites occurred at damaging levels on the station. Bulk corn fields were sprayed on July 24 at a rate of 0.08 lbs/acre with Capture insecticide (S, Fig. 1). The entomology experimental plots were sprayed on July 29 using various insecticides.

EFFICACY OF STANDARD AND SIMULATED CHEMIGATION APPLICATIONS OF INSECTICIDES FOR SECOND GENERATION CORN BORER CONTROL AND THEIR EFFECT ON SPIDER MITES, 1991
by Gary Dick, Phil Sloderbeck, Lisa Wildman, and Steven Posler* SUMMARY Several insecticides were evaluated for control of European corn borer and for their effect on spider mites on furrow-irrigated field corn. Corn borer oviposition was moderate to heavy in 1991. Eight of 13 treatments resulted in a significant reduction in numbers of fourth and fifth instar, European corn borer larvae compared to the untreated check. Nine of 13 treatments resulted in a significant reduction in proportion of plants infested with European corn borer compared to the untreated check. All treatments except the reduced-mite check resulted in a significant reduction in the amount of European corn borer tunnelling in corn stalks compared to the untreated check. The medium and high rates of Penncap-M 2FM ranked with the corn borer rates of Capture 2EC and Furadan 4L in effectiveness against European corn borer.
Banks grass mite was the predominant mite species present throughout the test period (98.9% and 97.3% Banks pre-and post-treatment, respectively). Significant differences occurred among treatments in their effect on spider mite numbers, but the usefulness of these data is questionable because spider mite numbers remained well below economic thresholds during the study period.

INTRODUCTION
This test was conducted to evaluate the efficacy of standard ground applications and simulated chemigation applications of several insecticides for the control of second generation European corn borer (ECB), Ostrinia nubilalis (Hübner), and southwestern corn borer (SWCB), Diatraea grandiosella (Dyar), on field corn in southwest Kansas. Populations of Banks grass mite (BGM), Oligonychus pratensis (Banks), and twospotted spider mite (TSM), Tetranychus urticae Koch, were observed to determine if any of the corn borer insecticides reduced mite numbers or caused spider mite numbers to "flare". PROCEDURES European Corn Borer. This test was conducted using a natural infestation of European corn borer in a furrow-irrigated corn field at the Southwest Research-Extension Center, Finney County, Kansas. Treatments were arranged in a randomized complete block design with four replications. Plots were four rows (10-ft) wide and 50 ft long with a 4-row (10ft) border of untreated corn on each side and a 10-ft alley at each end. Plots were treated using CO 2powered backpack sprayers with a tank mix of Banvel and Activator 90 on 19 June to control heavy populations of broadleaf weeds in the crop row that escaped pre-plant incorporated and post-emergence herbicide applications.
Simulated chemigation applications of insecticides were made using three Delavan 100/140, 3/4in, raindrop nozzles mounted on a high clearance sprayer at tassel height between rows. This system was calibrated to deliver the equivalent of a 0.2-in irrigation on the two center rows (5227 gal/a). Standard insecticide treatments were applied with a high clearance sprayer using a 10-ft boom with three nozzles directed at each row (one nozzle directly over the row and one on each side of the row on 18-in drop hoses) and calibrated to deliver 23.6 gal/a at 2.4 mph and 31 psi.
Ample first generation ECB larvae were collected from the plot field and other local fields between 27 June and 2 July in order to use Kansas State University's European Corn Borer Software model to predict the second generation egg laying period. The model predicted 25-50% oviposition to occur during a 9-day period from 19 July to 27 July, which is about the same as in 1990 but earlier than in 1989. The predicted oviposition period coincided with peak light trap catches of European corn borer moths at the SWREC. During this period, we examined the plot field and other local corn fields visually for corn borer oviposition in order to fine-tune the insecticide application date. The ideal target date for a single application of corn borer insecticides was 22-24 July (mid 25-50% oviposition range) according to the predictive model. We decided to treat on 24 July, but while we were waiting for the lower end of the field to dry sufficiently to enter with the high clearance sprayer, we received one or two heavy thunderstorms, which prevented us from making timely insecticide applications. Treatments were finally applied on 29 July, which was about 3-4 days past the optimal timing predicted by the model. This was not entirely bad, because the ECB oviposition period extended well past the model-predicted cutoff date. The fact that treatments were applied late should be taken into account when interpreting the data. Comite was applied to one set of plots to produce a "reduced-mite check" designed to prevent spider mites from rendering corn plants unsuitable as hosts for corn borers and to help us determine the effect of spider mites on corn borer populations and corn yields.
Corn borer counts were made in early September by dissecting a total of 15 corn plants from the two center rows of each plot (8 consecutive plants left row, 7 consecutive plants right row). The number of live ECB larvae, the number of plants with tunneling, and the total length (cm) of tunneling were recorded and analyzed using SAS Proc GLM.
Spider Mites. To determine the effect of corn borer insecticides on spider mite populations, two plants were selected in each of the two center rows (four plants total) of each plot and flagged. Prior to application of corn borer insecticides, naturally occurring populations of BGM were relatively evenly distributed and had reached numbers such that we believed artificial infestation would not be necessary. A pre-treatment count was made on 23 July by visually searching every other leaf (one-half plant) on the flagged plants for large (adult female) spider mites. Two post-treatment, half-plant, spider mite counts were made on 6 and 12 August. Results were converted to mean number of spider mites per one whole plant (n = 4) and analyzed statistically using SAS Proc GLM. On the first and last sample dates, samples of spider mites were collected from plants adjacent to the marked plants using a Henderson-McBurnie leaf brushing machine and mounted on glass slides for microscopic determination of species. Percent control of mites was calculated using the Henderson & Tilton formula, which adjusts the percent control in treated plots for increases or decreases in mite numbers that occur in the untreated check plot.
Harvest yields (bu/acre), adjusted to 15.5% moisture, were estimated by collecting the ears from the 15 plants split during the corn borer damage analysis and adjusting these values to 1 acre using established stand counts. Test weights (lb/bu) of samples were determined electronically using a Dickey-John GAC-II.

RESULTS AND DISCUSSION
European Corn Borer. The ECB light trap catch reached a 5-year high on the night of 19-20 July. Corresponding oviposition was heavier than it had been for the past several years and occurred over an extended period of time. In other local fields surveyed to fine-tune treatment date, European corn borer infestations ranged from 16 to 168 egg masses per 100 plants. In the study field at the time of treatment, the corn borer infestation was 22 egg masses per 100 plants and fresh eggs were still being laid. This test historically includes an evaluation of SWCB, but very few occurred in our plots in 1991. This is the third straight year that we have experienced very low SWCB populations.
Throughout the mid-late growing season, drought conditions prevailed and one or more irrigations were delayed or missed because of the need to schedule irrigation around our treatment applications. This resulted in severe moisture stress in parts of two blocks, and yield was very low and erratic in these areas. However, this did not appear to adversely affect European corn borer oviposition.
Eight of the treatments significantly (p < 0.01) reduced the number of live ECB larvae per 15 plants compared to the untreated check (Table 1). Nine of the treatments significantly reduced the proportion of plants infested with live ECB larvae compared to the untreated check. All treatments except the reduced-mite check (Comite) significantly reduced the length of ECB stalk tunneling compared to the untreated check. Capture 2EC, Furadan 4F, and the medium and high rates of Penncap-M 2FM resulted in generally acceptable (>70%) control of length of tunneling, but the reduction in length of tunneling was not statistically greater compared to other treatments except Javelin WG. The Bacillus thuringiensis products (Javelin, Dipel, and MVP) did not perform as well in this test as they have the last 2 years. The relatively good efficacy of Penncap-M and the relatively poor efficacy of B. thuringiensis products may have been due to the lateness of treatments relative to peak ECB oviposition. No significant occurred differences in yield among treatments because of the irrigation problems and correspondingly erratic growing conditions. Spider Mites. Banks grass mite was the predominant species present both before and 14 days after treatment (98.8% and 97.3%, respectively). Low numbers of TSM occurred in some plots but numbers were too low to have a significant impact on results of this test. Spider mite numbers reached only about 10% or less of the economic threshold in the most heavily infested plots. Overall, plots averaged only 12 mites per plant before treatment and 16 mites per plant 14 days after treatment.

EFFICACY OF MITICIDES AGAINST SPIDER MITES IN CORN, 1991
by Gary Dick, Phil Sloderbeck, Lisa Wildman, and Steven Posler SUMMARY Despite artificially infestation of the study field, spider mite numbers were quite low in 1991 compared to the previous 2 years. Natural populations of predatory mites and insects apparently kept spider mite populations well below economic thresholds. The species composition of spider mites present remained above 98% Banks grass mites during this test. Significant differences in number of mites occurred among treatments and blocks, but also significant treatment-by-block interactions for all sample dates. Even though some treatments appear to have resulted in significantly lower numbers of mites per plant, it is difficult to draw any definite conclusions from the data because mite numbers were low and not evenly distributed among plots. No significant corn yield differences occurred among treatments. The results of this study may not be broadly applicable. This test should be repeated in the presence of much higher numbers of spider mites before any general conclusions can be made.

INTRODUCTION
This trial was conducted to evaluate the efficacy of several miticides against the Banks grass mite (BGM), Oligonychus pratensis (Banks), and the twospotted spider mite, Tetranychus urticae Koch.

PROCEDURES
This experiment was conducted in a furrowirrigated corn field at the Kansas State University Southwest Kansas Research-Extension Center, Finney County, KS. Treatments were arranged in a randomized complete block design with four replications. Plots were four rows (10 ft) wide and 50 ft long with a 4-row (10 ft) border of untreated corn on each side and a 10-ft alley at each end. All treatments were applied on 8 and 9 August with a high clearance sprayer using a 10-ft boom with three nozzles directed at each row (one nozzle directly over the row and one on each side of the row on 18-in drop hoses).
The sprayer was calibrated to deliver 23.6 gal/a at 2.4 mph and 31 psi.
Unlike the situation in 1990, spider mite numbers remained very low well into the growing season. As a result, plots were artificially infested. Two plants were selected from each of the two center rows of each plot and flagged (four plants per plot). On 9 July, spider mite-infested leaves were collected from a cooperator farm approximately 10 miles southeast of Garden City, Kansas. These leaves were cut into small pieces and attached to the marked corn plants in each plot in order to initiate spider mite populations. A subsample of these leaf pieces (n=10) was determined to contain an average of 92 BGM and two predatory mites per piece. Infestations were somewhat successful in that small mite colonies became established. However, the rapid mite increase that so often occurs during favorable weather did not occur.
A pre-treatment spider mite count was made in each plot on 29 July by visually searching every other leaf (one-half plant) on the flagged plants for large (adult female) spider mites. Heavy rains following irrigation rendered the field too muddy to treat on the target date, 2 August. Because of the rain, the pre-treatment half-plant counts were repeated on 7 August. Treatments were applied on 8 and 9 August. A single post-treatment half-plant count was made on 16 August, 7 days after treatment (DAT). Results of each count were averaged over the four marked plants and analyzed statistically using SAS Proc GLM. Mean number of mites per half plant was multiplied by two, and the results are presented in Table 1 as mites per one whole plant.
On each sample date, samples of spider mites were taken from the four flagged plants in each plot using a vacuum sampler and mounted on glass slides for microscopic determination of species. On 16 August, plots were rated to determine if the sulfur treatments (TD-2322 and Microthiol Special) were phytotoxic.
Harvest yields (bu/acre), were estimated by collecting a 1/1000-acre sample of ears from an 8.7-ft section of each of the two center rows. The corn was shelled mechanically, weighed, and tested for moisture. The gross weight was adjusted to 15.5% moisture and converted to bu/acre. Test weights (lb/bu) of samples were determined electronically using a Dickey John GAC-II. Results are reported in Table 1.

RESULTS AND DISCUSSION
The mite species composition remained above 98% BGM throughout the study period and is treated as a single-species complex in this discussion. The stagnant nature of the mite population, despite general drought conditions for most of the summer, is indicated by the lack of substantial change in mite numbers between the first and second pre-treatment counts (Table 1). No significant differences occurred in corn yield among treatments. None of the treatments were phytotoxic. Highly significant differences (p<0.01) occurred in number of mites among treatment on all sample dates, as well as significant (p<0.01) block and block by treatment interactions. As a result, it is difficult to draw any definite conclusions from the data. Even though the number of mites appears to be significantly lower in some treatments, it is not clear whether this is a treatment effect or an artifact of the low and variable spider mite numbers. The percent control for each treatment was calculated using the Henderson & Tilton formula, which adjusts the amount of control based on an increase or decrease in number of mites in the untreated check. These data may not be truly representative of product performance under heavy mite pressure. In reality, much of the decrease in mite numbers was probably due to the activity of predatory mites and insects. Data on predator numbers were collected but have not yet been analyzed. Our overall conclusion is that treatment for mites would not have been necessary if these conditions had occurred in a commercial field. The greenbug is a native of Europe and was first detected in the United States in 1882. Originally, it was described as a pest of wheat and other small grains. Over the years, several different types of greenbugs have been described based on their response to different host plants or pesticides (see Table 1).
It is now generally accepted that the term biotype should be reserved to describe an insect's response to its host plant. Therefore, we will not define the new pesticide-resistant greenbugs as being a new biotype. Currently, we are still unsure what, if any, significance to give to the Type 1 vs. Type 2 pesticide resistance. These names are based on the fact that we observe dark bands at two different locations on a gel electrophoresis plate. Work is currently underway to determine any real biological differences exist between these two types of banding patterns. These data may be available in the near future.
So far, all of the pesticide -resistant greenbugs we have sent to Dr. Tom Harvey at Hays and Dr. Gerald Wilde at Manhattan have been identified as Biotype E based on their response to host plants. However, greenbugs collected from Stevens County during 1990 were found to be a new biotype based on their ability to damage most Biotype E-resistant sorghums and were named Biotype I. It is too early to tell what this discovery will mean to Kansas sorghum producers, but if it spreads as rapidly as Biotype E, it may become the predominant type within a few years.
Thus currently, four different types of greenbugs are known to be present in Kansas: Biotype E that are susceptible to pesticides. Biotype E that have Type 1 pesticide resistance. Biotype E that have Type 2 pesticide resistance. Biotype I that are susceptible to pesticides.  To date, we are still working to determine if pesticide resistance is present in the new Biotype I greenbugs. As mentioned earlier, all of the pesticideresistant greenbugs appear to be Biotype E. However, we have not tested a large enough number of Biotype I greenbugs to be sure they aren't occasionally also pesticide-resistant. Biotype I is suspected to be pesticide-resistant based on the similarity of its distribution patterns to those of pesticide-resistant greenbugs. The worst case scenario would be for the new Biotype I greenbug to have pesticide resistance.
Because this is a rapidly changing and confusing issue, please feel free to call Leroy Brooks or Phil Sloderbeck if you have any questions about the status of greenbug biotypes or pesticide resistance. We will continue to monitor the greenbug populations and hope to have more data on the pesticideresistant greenbugs soon.
The results of surveys conducted to determine the distribution of these different types of greenbugs are shown on the following maps. Basically, pesticide-resistant Biotype E greenbugs have been reported from five states (Kansas, Nebraska, New Mexico, Colorado, and Texas (Fig. 1)). The new Biotype I greenbugs have been found in four states (Kansas, Nebraska, Colorado, and Texas (Fig. 2)).
Pesticide-resistant greenbugs and Biotype I greenbugs were easy to find in Southwest Kansas during 1991 (Figs. 3 and 4). However, luckily the weather did not seem to be just right for a greenbug outbreak, and very little insecticide was applied. Where treatments were used, parasites and predators were able to quickly eliminate the remaining greenbugs. Thus, growers didn't really notice that the resistant greenbugs were present. This is in contrast with 1990, when parasites and predators were scarce, the resistant greenbugs left after the initial insecticide application soon rebounded to damaging levels, and additional sprays were ineffective.

SUMMARY
Many treatments provided good kochia and pigweed control. However, only the experimental compound San 582 + atrazine at 1 + 1 lbs ai/A, San 582 + Marksman at 1 + 1 1/4 lbs ai/A, and Lasso + atrazine at 2 + 1 lbs ai/A provided season-long control of kochia, pigweed, and foxtail. Analysis of pigweed and foxtail control was complicated by intense kochia competition. In general, preemergence herbicide programs outperformed total postemergence herbicide tank mixes.

PROCEDURES
Furrow-irrigated corn was planted as described in Table 1., and herbicide treatments were applied pre-post-, and late post-emergance with a tractormounted CO2-pressurized sprayer as described in Tables 2,3, and 4.

INTRODUCTION
More than 32 herbicides and many more combinations of these herbicides are commonly used in field corn. This test compares many, but certainly not all postemergence herbicides, to three effective preemergence herbicide programs. Treatments were arranged in a randomized complete block design with four replications. The percent weed control was calculated by dividing the number of a specific weed species per unit area in the treated plots by its corresponding control plot, subtracting this from 1, and multiplying the difference by 100.

RESULTS AND DISCUSSION
No herbicide treatment caused commercially significant injury to corn. However, all Buctril treatments caused statistically significant, albeit minor leaf speckling, which equated to 9.25 to 9.5% visual injury. In general, only those treatments containing atrazine provided good kochia control (Table 5. Treatments 4,8,9,23,26.). Treatments 1, 21, 22, and 24 provided poor kochia control although they contained atrazine. This poorer kochia control might be attributed to reduced efficacy of postemergence applications.
Although most treatments provided excellent pigweed control, in many instances, kochia competition was a significant component of pigweed control (Table 6). For example, treatments 5, 12, and 22 provided very poor kochia control, which, in turn, produced higher levels of pigweed control than expected. This additional control was probably due to kochia competition. Therefore, only those treatments that produced excellent kochia control should be used to compare pigweed control. For example, only treatments 1, 2 3, 4,7,8,9,17,19,20,23, and 25 produced kochia control sufficient to allow the reader to conclude that subsequent pigweed control was due to herbicide treatment not kochia competition.
Kochia control also confounds the analysis of foxtail control (Table 7). Only in this instance, kochia control lead to dramatic increase in foxtail numbers. Once again, the reader is advised to consider the level of kochia pressure in this test when comparing foxtail control.  _______________________________________________________________________________________________________________________ * More present than in the control.

EFFECTS OF TIME OF APPLICATION OF 8 HERBICIDE COMBINATIONS FOR WOOLYLEAF BURSAGE (BUR RAGWEED) CONTROL
by Randall Currie, Dave Rust, and Peg Steward* SUMMARY Several herbicides were compared for woolyleaf bursage control in fallow. Tordon + 2,4-D at 0.25 + 1.0 lb ai/A and Tordon + Banvel at 0.25 + 0.50 lb ai/A applied at flowering controlled wooly leaf bursage 99.5% and 81.5%, respectively, 350 days after treatment, as compared to 88.5% and 80.8% control, respectively, for these two treatments applied after a light frost. XRM 5084 + Banvel at 0.375 + 0.5 lbs ai/A provided 86.4% control. All other treatments provided less than 77.4% control.

INTRODUCTION
Woolyleaf bursage, also known as bur ragweed, is a noxious perennial weed found most frequently in low lying areas of fields. It is also found in the higher areas of fields because of movement of root stocks and seeds by tillage equipment. Once established, this weed is difficult to control. The objective of this study was to compare several herbicides applied at flowering and after frost for control of woolyleaf bursage.

PROCEDURES
The study was established in August, 1990. The experimental design was a two factorial randomized complete block with two levels of application timing, nine levels of herbicide treatment, and three replications. Herbicides were applied with a CO 2 -pressurized, hand-held sprayer equipped with a six-nozzle boom. Application volume was 20 gallons per acre. Herbicides were applied on August 15, 1990 at flowering and on September 13, 1990, after a light frost.
On April 25, 1992, a tank mix of Surflan, Bladex, and atrazine at 2, 4, and 2 lb ai/A was applied to the entire plot area to control all weed species but bur bagweed. The treatments were evaluated for weed control 255 and 350 days after treatments. The percent weed control was calculated by dividing the number of a specific weed species per unit area in the treated plots by it's corresponding control plot, subtracting this from 1, and multiplying the difference by 100.

RESULTS AND DISCUSSION
No late fall treatment outperformed herbicide applications at flowering 350 days after application. In only one instance, Stinger at 0.67 pt/A, did a late fall application outperform an at-flowering treatment 255 days after treatment (Table 1).
Only those treatments that produced greater than 37.8% control 350 days after treatment had any statistically significant impact on bur ragweed growth. Any treatment producing at least 61.7% control was not statistically significantly better than the best treatment, Tordon 22K + 2,4-D at 1 + 2 pts/ A, which produced 99.5% control 350 days after treatment. This treatment was also rated as the most effective by Morishita under similar conditions near the S.W.R.E.C. in 1988.
Although labeled, Tordon can severely injure wheat under dry conditions that do not facilitate its breakdown. Tordon can also eliminate all weed cover during the fallow period, greatly enhancing the risk of severe wind and water erosion if very careful residue management is not practiced. *Personal Consultant, Diamond Ag Research, Garden City. This study is based on only one year's data. Management decisions should not be made solely on the information provided here. Always remember to read and follow all label instructions when using any pesticide and be advised that it is a violation of federal law to use any pesticide inconsistent with its labeling. 2 Control is based on aboveground growth as a percentage of the untreated check. Aboveground growth was estimated by multiplying the average height times the average number of stems per unit area. 3 A negative number indicates that more bur ragweed was found in these treatments than in the untreated control. In no case was this increase statistically significant. SUMMARY All Accent or Beacon treatments at full labeled rate preceded by any preemergence treatment provided excellent shattercane, pigweed, and kochia control. Although 1/2 X rates of Accent and Beacon used in combination with preemergence herbicides frequently provided very good control of these weed species, control was more variable.

INTRODUCTION
Shattercane is a weed that causes serious problems for corn growers. It is highly competitive and difficult to control. Accent and Beacon are sulfonyl urea herbicides for controlling shattercane in corn. The objective of this study was to compare these two compounds at 1 X and 1/2 X rates with and without several preemergent herbicide treatments for shattercane control in corn.

PROCEDURES
Furrow-irrigated corn was planted as described in Table 1., and herbicide treatments were applied pre-and postemergence with a tractor-mounted CO 2pressurized sprayer as described in Tables 2. and 3. Treatments were arranged in a randomized complete block design. The percent weed control was calculated by dividing the number of a specific weed species per unit area in the treated plots by it's corresponding control plot, subtracting this from 1, and multiplying the difference by 100. The original intent of this experiment was to apply only full label rates of Accent or Beacon in two split 1/2 X rate applications. Weather did not permit the second application of Accent or Beacon; therefore, evaluations of a total postemergence weed control program are not possible.

RESULTS AND DISCUSSION
Although the data show several strong trends, these are based on only one years' data and the distribution of weed species varied across the test. Therefore, the reader should use these data only as a very loose guide.
In general, any preemergence product followed by a full rate of Accent or Beacon provided good  4, 5, 6.). Although many preemergence treatments followed by a half rate of Accent or Beacon performed well, these combination were more variable. Unfortunately, weather did not allow the second application of Accent or Beacon to treatments 16 or 17, so comparisons of full rates of these compounds by themselves could be made. Also, we should point out that a low level of Bicep ($13.05/A) is being compared to a higher rate of Eradicane + Atrazine or Sutan + Atrazine ($29.24 and $23.49, respectively). Although there are some exceptions, increases in herbicide cost generally equated to increased weed control which in turn translated into higher yield.

SUMMARY
Irrigation frequency did not affect yields. Therefore, switching to an LEPA system and applying smaller amounts to minimize runoff should not affect yields adversely. Yield was significantly reduced by underirrigation and was not significantly increased by overirrigation.
LEPA is easier to justify when purchasing a new sprinkler because the cost difference is smaller (approximately $5,000). Converting an existing system to LEPA is much harder to justify, unless water costs are high and the producer is currently underirrigating the crop.

INTRODUCTION
A Low Energy Precision Application (LEPA) sprinkler system was installed at the Southwest Research-Extension Center in 1989. This report summarizes the frequency and amount results and procedures for 1989, 90, and 91.

PROCEDURES
Corn was planted in a circle. The system was run around once to establish the tower tracks, which were used as markers. The corn was planted in a circle from the even towers (i.e., towers 2, 4, and 6) out to the odd towers.
Aluminum access tubes were installed for use with a neutron probe to determine soil water. Measurements were taken weekly to verify crop water use estimates and were used to calculate the change in soil water over the season.
The field was furrow diked to help prevent runoff. Dikes or deep ripping are used with LEPA systems to store water for infiltration and prevent excessive runoff.
Irrigation treatments of 0.4, 0.7, 1.0, and 1.3 times the base irrigation (BI) amount were used. The rated flow was changed for the nozzles by the respective percentage. Irrigation frequencies of 3, 6, and 9 days were also used. Each treatment was replicated four times. Plots were then irrigated every 3, 6, or 9 days with the bubble mode and the desired fraction of BI. We replenished the amount of water used during each time interval at the end of that interval.
Irrigation amounts for each plot varied by treatment and frequency. Application amounts ranged from 0.2 to 3.8 inches per irrigation event. The 3-day frequency was used to study the effects of high frequency applications. LEPA systems (bubble mode) will probably require amounts less than 1 inch because of high runoff potential. The 9-day frequency resulted in very high water applications for LEPA but the plots were bordered to contain the water. Thus, the 9-day treatment resembled low frequency irrigation like furrow irrigation.
Forty feet of row were hand harvested from each plot. Yields were adjusted to 15.5 percent moisture and are reported in bushels per acre.

DISCUSSION
This study was patterned after a study at Texas A & M conducted by Dr. Bill Lyle. The Texas study used the same amount and frequency treatments but added a 12-day frequency.
These data (Figure 1) and the Texas data show that irrigation frequencies of 3, 6, and 9 days are not significantly different. Because of scheduling conflicts, our "3-day" treatment was actually 3.5 days and our "9-day" treatment was actually every 10.5 days. Therefore, our "9-day" frequency tended to have lower yield. The 12-day yields (Texas) were significantly lower than those for the 3-, 6-, and 9day treatments. Yields for all treatments are given in Table 1. These data indicate no yield losses when high frequency irrigation is required, such as for an LEPA system. The seasonal soil water change is given in Table 2. A negative value shows that water was extracted from a 5 ft. profile between June 30 and September 22   Figure 2 shows that yields level off for amounts greater than 1.0 BI. This presents a case for using irrigation scheduling to help the producer obtain optimum yield without wasting water. As expected, corn yields increase significantly with irrigation amounts up to 1.0 BI. A significant difference occurred between yields for each of the two low BI treatments but not between the two high BI treatments.

45
(1989), June 27 and October 3 (1990), and June 3 and September 19, 1991. Soil water was monitored in the 3.5-and 10.5-day treatments for each replication in 1991. In 1989, only one replication was monitored. In the underwatered irrigation treatments, water was generally extracted from the soil profile to help meet the crop's water needs.
Similar results were obtained for each year, despite the difference in rainfall. We received 11.5 inches of rainfall during the 1989 growing season, 3.8 inches in 1990, and 8.0 inches in 1991. The irrigation amounts applied were 11.9 inches in 1989 and 22.2 in 1990 for the 1.0 BI treatment. Irrigation amounts were evened up among frequency treatments in 1989 with the last irrigation. The amounts were the same for 1990. Irrigation amounts for each treatment for 1991 are given in Table 3. furrow diked in 1989 because fields were too wet from excessive rainfall during June, which may be why yield was lower. Improved corn yields might have resulted from using the flat spray mode rather than the bubble mode. The current cost to convert an existing system to LEPA is approximately $10,000. It is hard to justify conversion unless fuel costs are high and water is limiting (i.e., the producer is currently underirrigating). However, the difference in cost between spray heads and LEPA heads (approximately $5,000) for new installations can be paid off in a 3-to 5-year period, depending on fuel costs and corn prices. Total water use is shown in Table 4, which includes seasonal soil water change, irrigation, and rainfall amounts. The long-frequency plots required less irrigation water because they had more opportunity to capture rainfall. If plots had been managed at some value less that "field capacity", similar irrigation amounts would have resulted.
The total water use and irrigation water applied were used to calculate total water use efficiencies (TWUE) and irrigation water use efficiencies (IWUE). Both are shown in Table 5. Water use efficiency is defined as the corn yield divided by the appropriate water quantity (bu/a-in).
The LEPA concept is to keep every other row dry to reduce evaporation losses. Slopes greater than 0.5 to 1.0 percent will produce significant runoff and reduced yield. Therefore, furrow diking is recommended for all LEPA systems. The plots were not SUMMARY Soybean yields were good and increased with increasing water applied. Yield was 60 bu/a for beans watered at 40 percent of the base irrigation (BI) requirement. Past research has shown that the water use curve is usually flat and may decrease with overwatering. This did not happen in 1991 for our conditions. Therefore, additional years of data will be collected to determine the response of soybeans to irrigation water applied using the LEPA bubble mode.

INTRODUCTION
A Low Energy Precision Application (LEPA) water requirement study for soybeans was initiated in 1991. LEPA irrigation should deliver 95 percent or more of the water to the soil. This highly efficient method of irrigation coupled with keeping every other row dry should produce good to excellent soybean yields.
The objectives of the study are: 1) to determine the water requirement of soybeans irrigated with a LEPA system in the bubble mode and 2) to establish management criteria for irrigating soybeans with a LEPA system.

PROCEDURES
Soybeans were planted in a circular pattern. The center pivot was run around the field once to establish tower tracks, which were used as markers for the planter to follow. The soybeans were planted on May 15 from the even towers out to the odd towers. The field was furrow diked to prevent runoff.
Aluminum access tubes were installed to measure soil water with the use of a neutron probe. Measurements were taken weekly to a depth of 5 feet to calculate the change in soil water over the season.
Treatments of no irrigation, 0.4, 0.7, 1.0, and 1.3 times the base irrigation (BI) were used. Each treatment was replicated five times. One irrigation (0.60 inches) was applied at 100 percent for all treatments early in the season on June 18. This occurred before the system was modified to put on fractional amounts of water for the various treatments. Irrigations were generally 1 inch, except for the first and second irrigations. The second irrigation was 2.75 inches because it was delayed while modifications were still being made the the system.
Twenty feet of row were harvested from each plot. Yields were reported in bu/a and adjusted to 13 percent moisture.

RESULTS AND DISCUSSION
The yield and water use data are given in Table  1. Yield by treatment is also shown in Figure 1. Yields increased with increasing water applied. Past research has shown yield response to water applied for soybeans to be relatively flat. Yield can decrease with overwatering in some years.

treatments.
Although we felt we did not stress the fully watered plots, the yield continued to increase with increasing depths of applied water. Figure 2 shows the average volumetric soil water content for the 5 ft. profile by water treatment throughout the season. Soil water contents were very similar for the 1.3 and 1.0 BI treatments. Soil water content did decrease with time for the underwatered treatments.
These are data for only one year, and additional climatic years are required to draw any useful conclusions. For the conditions encountered, LEPA in the bubble mode with furrow diking performed well.

48
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information is available from http://www.ksre.ksu.edu.

INTRODUCTION
Low Energy Precision Application (LEPA) sprinkler systems produce high application rates because of the small wetted diameters of the nozzles. On sloping ground, this can cause considerable runoff. A study was initiated in 1990 to provide producers with effective guidelines for managing LEPA systems on slopes greater than 1 percent.

PROCEDURES
Corn was planted in a circlular pattern. Various tillage treatments and spray modes were used to determine which combination reduced runoff the most. Slopes ranged from 1 to 6 percent and averaged 3 percent. Bubble-mode plots had a higher average slope than did the flat-spray plots.
Tillage treatments included furrow diking (forming basin reservoirs between rows), in-furrow ripping, and implanted reservoirs in combination with ripping. Dikes and small reservoirs dug into the soil surface are used to hold water until it can infiltrate into the soil. Ripping is used to increase the intake rate of the soil.
All treatments were irrigated by the bubble and flat spray modes. The bubble mode concentrates the water into a small area directly beneath the nozzle (approximately 1.3 ft. in diameter). The flat spray spreads the water out over a greater area (approximately 10 ft.).
Aluminum access tubes were installed for use with a neutron probe to determine soil water content. Soil water measurements were taken weekly to calculate the change in soil water over the season.
The first irrigation was on June 17, and plots were irrigated approximately once a week thereafter. The irrigation application amount was kept at or below one inch, the current recommendation for flat slopes. Borders were installed across the field to prevent water from one treatment from running onto any treatment further downhill.
Forty feet of row were hand harvested from each plot. Yields were adjusted to 15.5 percent moisture and are reported in bushels per acre.

RESULTS AND DISCUSSION
Runoff rates were so high in the bubble mode that corn yields were reduced (Figure 1). Ripping and furrow diking increased yields slightly (Table 1). Diking with ripping increased yields the most (Figure 2).  Diking with ripping had the greatest effect on yields when the bubble mode was used. This could be because of the increased intake rate with ripping and because this treatment had the best reservoirs. The flat spray mode showed less sensitivity to tillage treatment because of the larger area wetted as compared to the bubble mode.
The seasonal soil water change for the period between June 3 and September 19 is given in Table 2. Total water applied is shown in Table 3. This includes the seasonal soil water change, irrigation, and rainfall amounts. Rainfall amounts were 3.8" and 8.0" for 1990 and 1991, respectively. Irrigation amounts were 21.1 and 16.7 inches for 1990 and 1991, respectively. Not all of the water applied was available for use by the crop because of runoff from the plot area.

51
The total water and irrigation water applied were used to calculate total water use efficiency (TWUE) and irrigation water use efficiency (IWUE). Both are shown in Table 4. Water use efficiency is defined as the corn yield divided by the appropriate water quantity.
The bubble mode would work well under conditions where the reservoirs can hold all the water applied. Reservoir tillage was effective in reducing runoff and holding water where it was applied. Diking with ripping worked best on the slopes studied (1 to 6 percent). The flat spray mode was more effective in minimizing runoff than reservoir tillage. The combination of flat spray mode and reservoir tillage produced the highest yields.

INTRODUCTION
Interest in low pressure spray devices has increased greatly in recent years. Greater management is necessary because of the increased potential for runoff. In some cases, the nozzles have been placed just above the ground surface. This introduces an additional problem of interception of the spray by the crop for nozzle spacings that do not provide every row with an equal opportunity for water (i.e., spacings greater than 5 ft-every other row for circular rows). The amount of water saved by moving the nozzles from the truss rod height to 2 ft off the ground may not justify the additional cost, especially if runoff (nonuniformity within the field) becomes a problem.
Most systems do not fit the definition for LEPA (Low Energy Precision Application). LEPA systems by design must use reservoir tillage to maximize capture of rainfall in and out of season. Reservoir tillage is used on all slopes to maximize uniformity of rain and irrigation water. LEPA systems should also keep every other row dry (i.e., use the bubble mode or double-ended socks) to minimize evaporation of water from the soil surface. Another requirement for LEPA is keeping all traffic out of the row that receives water so that compaction is minimized and intake rates are maximized. Very little LEPA irrigation is being done in Southwest Kansas. However, we can improve the efficiency of the water delivered to the soil, but it may take several years to pay for the additional hardware with water and energy savings.
The objective of this study was to determine the effect of in-canopy flat spray nozzle spacing on corn yield. This study was mainly a reconnaissance mission to determine the potential for further investigation.

PROCEDURES
Corn was planted in circular rows in a deep silt loam soil. The nozzles tracked well between corn rows. Soil slope was generally 0 to 1 percent. The field was furrow diked to minimize runoff.
Treatments consisted of LEPA nozzles (6 psi) operated in the flat spray mode placed in every other row (5 ft spacing) and Low Drift Nozzles (LDN) (10 psi) placed in every 4th row (10 ft spacing). All nozzles were 2 to 3 ft from the ground surface.
No soil water data was taken. This study will be expanded for 1992 and include soil water measurements and a 15-ft spacing treatment. Irrigation depth was generally kept at 1 inch. The soil water was depleted slightly more than planned (greater than 25 percent) during the third week of August because of scheduling conflicts.
Irrigation for all plots totaled 16.5 inches. Rainfall from June 5 to September 19 was 8.5 inches.

RESULTS AND DISCUSSION
Yield from the study by row position relative to the nozzle position is shown in Figure 1. Yield for the 5 ft spacing was 205 bu/a. Samples taken next to the nozzles spaced at 10 ft yielded 218 bu/a and samples taken between the nozzles yielded 205 bu/a. No statistics were run on the data because of the small difference in yield and small number of treatments. However, the data indicate that we should continue investigation of effects of in-canopy nozzle spacing on yield and include soil water measurements.
We should be concerned about fields with slopes greater than one percent. Steeper slopes will cause more runoff, especially for the 10-ft. nozzle spacing as the spray gets intercepted by the growing crop.

SUMMARY
A drip-line spacing and plant population study for corn was conducted in 1989, 90, and 91. Threeyear average yields ranged from 187 to 216 bu/a for line spacings of 10 to 2.5 ft, respectively. Yields were lower from the 7.5 and 10 ft. spacings than from the 2.5 ft. and 5.0 ft. spacing. The soil water content decreased in the upper 2 to 3 ft as close as 15 inches from the drip line. Yields from population treatments were different and peaked at 212 bu/a for the INTRODUCTION Water tables in southwest Kansas are declining; therefore, producers want to use their water efficiently to allow the resource to last as long as possible. Producers might consider drip irrigation to save water, if production were profitable.
A drip irrigation study was initiated at the Southwest Research-Extension Center in 1989. Objectives of the study are: to determine (1) optimum plant population, (2) the effect of drip line spacing on yield, and (3) the effect of drip line spacing on water movement.

Plot Layout
The field was fertilized with 240 lbs of nitrogen and 40 lbs of phosphorous. Drip lines were buried 16 inches below the ground surface and spaced 2.5, 5.0, 7.5, and 10 ft apart in a silt loam soil. Corn was planted in 30-inch rows perpendicular to the drip lines and thinned to populations of 38,000, 32,000, 26,000, and 20,000 plants/a. Each plot consisted of four crop rows. Populations were replicated four times.

Soil-Water Monitoring Method
Aluminum access tubes were installed in increments of 7.5 inches from a drip line in each spacing replication. The access tubes were installed in the 32,000 plants/a population treatment. A neutron probe was used weekly to determine the soil water status.

Irrigation Method
All spacing treatments were irrigated to apply 100 percent of evapotranspiration (ET -crop water use). Therefore, each plot received the same gross average depth. The wide spacing treatments received enough water to cause deep percolation. This was done so that maximum horizontal water movement was not hindered. The drip lines were 195 ft long and were rated at 0.3 gpm per 100 ft.
Set times for the various spacings needed to apply an average depth of 0.5 inch over the plot area were: 4.3 hr for 2.5 ft, 8.6 hr for 5.0 ft, 13 hr for 7.5 ft, and 17.3 hr for 10 ft. Set times were reduced slightly by operating the system at 15 psi rather than the suggested pressure of 10 psi. A measurable plant height decrease, about 18 inches, occurred between drip lines for the wide spacings.
The first irrigation was applied on June 7. Plots were irrigated by replenishing ET after the soil water deficit reached at least 0.5 inches. Irrigation was applied when the soil water deficit was between 1.00 and 1.75 inches to allow for the beneficial use of rainfall. Totals of 13.0, 21.9, and 17.2 inches of irrigation water were applied in 1989, 1990, and 1991, respectively. Rainfall amounts were 11.5, 3.8, and 8.0 inches, respectively. About 2 inches of water were lost to deep percolation in both 1990 and 1991 because of rainfall events following irrigations.

Harvest Samples
Each plot consisted of four corn rows and four drip lines. The two middle corn rows were used for yield samples. One row was used for bulk yield samples and the other row for individual plant yield. Because the drip lines were perpendicular to the corn rows, the length of row harvested was equal to two times the drip line spacing. The sample began halfway between the first and second drip lines and spanned across the two middle drip lines.

DRIP-LINE SPACING AND PLANT POPULATION FOR CORN
by William Spurgeon, Thomas Makens, and Harry Manges*

Data Analysis
Both bulk yield and individual plant yield samples were taken. An analysis of variance was performed on the bulk yield samples for population and drip-line spacing treatments. Individual plant yield (mass of grain per plant) was collected but has not been analyzed. Figure 1 shows the 3-year average yield for the various populations for each spacing treatment. Also, the 3-year average population treatment yields are shown in Figure 2.

Plant Population
Yields for 1989, 90, and 91 are given in Table 1. Yield differences were statistically significant and peaked for 32,000 plants/ac.

Drip-Line Spacing
Three-year average yields for the spacing treatments are shown in Figure 3. Yields were higher for narrow drip-line spacing, although they stayed relatively high for the wider spacing. Soil Water Movement Soil water content was monitored weekly to a depth of 8 ft. Access tubes were placed at 15-inch increments away from the drip lines in 1989, and 7.5 inches in 1990 and 91. This was done for all of the spacing treatments in the 32,000 plants/a population treatment.
The average volumetric soil water contents for the upper 5 ft at 3, 15, 30, 45, and 60 inches from the drip line for one of the 10-ft spacing treatments are shown in Figure 4 for 1991.
Also, rainfall and irrigation events are shown.
We were able to maintain high soil water contents 15 inches from the drip line. Soil water content decreased as the distance away from the drip line increased and approached a value dependent on rainfall rather than irrigation. Our data show that volumetric soil water content approached 50 percent depletion at 45 and 60 in. from the drip line. This dry region extended 2 to 3 ft below the soil surface for both the 7.5 and 10 ft spacing treatments. Corn height was about 1.5 ft shorter between drip lines for the 7.5 and 10 ft spacings.

56
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived. Current information is available from http://www.ksre.ksu.edu.
Objectives of the study are to determine: (1) the effect of length of drip lines on corn yield and (2) the effect of water flow upgrade and downgrade on corn yield.

Plot Layout
Drip lines were buried 16 inches below the ground surface and spaced 60 inches apart in a silt loam soil. Four drip lines were used per length treatment, and lengths were 330 ft. and 660 ft.. For each length, the water flowed from the up or downslope end. Also, one of the 660 ft. treatments had water pumped in from both ends. The slope was about 0.15 percent. Corn was planted on April 23, 1991 in 30-inch rows parallel to the drip lines. Each plot consisted of eight crop rows.

Soil-Water Monitoring Method
Aluminum access tubes were installed in the corn rows and were 15 inches from the drip line.
They were read to a depth of 8 ft. A neutron probe was used weekly to determine the soil water content.

Irrigation Method
All treatments were irrigated to apply 100 percent of the Base Irrigation (BI) requirement in 1990 and 75 percent in 1991. We thought that the reduction in irrigation level in 1991 might impose greater stress on the corn for the longer length plots. This was done so that any existing differences would be more evident. Plots were irrigated when the depletion reached 1 inch. The first irrigation occurred on June 16. Plots were irrigated by replenishing the appropriate fraction of BI. A total of 15.7 inches of irrigation water was applied in 1991 (19.3 inches in 1990). Rainfall was 7.5 inches during the season (9.2 inches in 1990).
The drip lines were rated at 0.25 gpm per 100 ft. A pressure of 10 psi was maintained on all plots.

Harvest Samples
Each plot consisted of eight corn rows and four drip lines. The two middle corn rows were used for yield samples, 20 ft. of row was harvested in each. The 660 ft. length was harvested at both ends and two places along its length. The 330 ft. length was harvested at both ends.

Data Analysis
Corn yield per acre was calculated from each of the sample areas. The yields were adjusted to a 15.5 percent moisture content. An analysis of variance showed no difference among corn yields.

RESULTS AND DISCUSSION
Two seasons (1990 and 91) of data have been collected. Figure 1 shows differences in average yield for the 2 years. However, the differences were not significant nor consistent with the differences expected. We would have expected the 330 ft. downslope flow to have the highest yield and the 660 ft. uphill flow to have the lowest.

DRIP-LINE LENGTH STUDY by William Spurgeon, Thomas Makens, and Harry Manges
A hail storm on July 19, 1990 affected yield at various locations in the field. Lower yields occurred on the west end of the field (the uphill end), causing the 330 ft. downhill treatment to have lower than expected yield. Yield by position is given in Table 1. Table 2 shows total water use by position for each treatment for 1990 and 1991. These data show little change in water use by position for all treatments, indicating that the long lengths (660 ft.) performed quite well.
A portion of the cost of drip installation is in feeder lines that supply water to the drip lines. Therefore, assuming less yield difference when hail damage is not present, longer lengths of drip line may be used to reduce installation costs.

INTRODUCTION
Subsurface drip was used to irrigate corn in Holcomb, Kansas. This is a method of supplying low volumes of water to the root zone, thus minimizing evaporation losses and potentially reducing deep percolation losses. Eight different frequencies of irrigation were used, and the yields were compared.
The objectives of this study are to determine: 1) the effect of frequency and amount of irrigation on crop yield and 2) soil water content.

PROCEDURES
Drip lines were buried 16 inches deep in the center of each bed and ran parallel to the crop rows. Therefore, each drip line supplied water to two corn rows 15 inches away. The corn was planted on 60-inch beds. The study consisted of eight watering treatments. The treatments were 1-, 3-, 5-, and 7day watering intervals and 0.5-, 1-, 1.5-, and 2-inch depletion levels. The evapotranspiration (ET) was calculated to determine the amounts to be watered for each treatment. The depletion level treatments were watered when depletion reached the stated amount, and frequency plots received the amount of water used during the specified interval.
Access tubes were installed in every plot in the corn row, 15 inches from the drip line, for use with a neutron probe. The neutron probe was used to determine soil water to a depth of 8 ft. The soil water was monitored weekly. The larger amount and less frequent irrigation treatments generally dried out more between irrigations.

RESULTS AND DISCUSSION
Statistically, no differences occurred among the yields of the different treatments (Table 1). In 1990, the highest yielding plot was the 7-day treatment with 181 bu/a and the lowest was the 3day treatment with 162 bu/a. In the second year, the highest was the 1-day treatment with 225 bu/a, and the 5-day treatment was lowest with 205 bu/a. Because of this lack of statistical difference and the uneven damage caused by a July 19, 1990 hail storm, it is difficult to draw any conclusions. Figure  1 shows the 2-year average yield by treatment and indicates very few differences.
The total water applied differed between treatments (Table 2). Rainfall was 9.2 inches in 1990 (June 6-September 24) and 7.5 inches in 1991 (June 1-September 17). The less frequent treatments with larger amounts allowed the soil to dry out between irrigations; thus, it had the ability to store rainfall. Because irrigating 1 inch takes 21 hours, the frequency of applying this amount is limited. All treatments were brought back to field capacity at each irrigation. Also, we continued to irrigate during rain storms to stay consistent and to avoid the error that would be caused by variations in the irrigation amounts. However, practical management, i.e., leaving a deficit for the storage of rainfall, could reduce irrigation amounts .

INTRODUCTION
This study was designed to evaluate the use of buried drip line irrigation for corn in Holcomb, Kansas. The corn was irrigated at various fractions of the Base Irrigation (BI) required.
The objectives of this study are: 1) to determine the water requirement of corn grown with drip irrigation and 2) examine the feasibility of largescale adoption of drip irrigation for row crops in Southwest Kansas.

PROCEDURES
Corn was planted in 30-inch rows on 60-inch beds. Each bed was irrigated by a drip line running through the center of the bed, 16 inches deep. Each drip line watered two corn rows, 15 inches to either side of the line. There were six irrigation treatments. They were no irrigation, irrigation at 0.25, 0.5, 0.75, 1.0, and 1.25 times BI.
Access tubes were installed in every plot in the corn row, 15 inches from the drip line, for use with a neutron probe. A neutron probe was used to determine soil water to a depth of 8 ft. Also, access tubes were placed at 3, 15, and 30 inches from the drip lines in the 1.25, 1.0, 0.75 and 0.5 BI plots. This enabled us to study the horizontal movement of water away from the drip line.

RESULTS AND DISCUSSION
Differences in yields were observed for the harvest (Table 1 and Figure 1). A hail storm in July 1990  reduced yields. The 1.0 BI treatment received 20.1 inches of irrigation water in 1991. Rainfall was 7.5 inches for the season. The 1.0 BI treatment had the highest 2-year average yield, 197.0 bu/a. The 1.25 BI treatment yielded 193.6 bu/ a. The increased amount of water did not increase yields. This may have been due to loss of aeration.
Irrigations were frequent, and small amounts were used. Soil water status by BI level throughout the season is shown in Figure 2. Analysis of a similar drip water requirement study at Colby indicated that the 0.75 BI level had slightly reduced yield (6% reduction from 1.0 BI). The best management for drip would be to maintain the soil water at some level less than field capacity. This should be done to help capture more rainfall and minimize drainage losses. Irrigations should be frequent enough to prevent stress. At least a 15 to 20% savings on water is realized by managing a buried drip at values less than field capacity with little or no reduction in corn yield.