Southwest Research-Extension Center, Field Day 1997

Report of agricultural research from Southwest Research-Extension Center of Kansas State University.


WEATHER INFORMATION FOR GARDEN CITY
by Jeff Elliott -13º, -12º falling on three consecutive nights beginning on February 2nd. Temperatures of 100º or above occurred on 6 days, with the highest being 103º on May 19 and July 5.
The last spring freeze (31º) fell on May 1, 4 days later than average. The first fall freeze (23º) occurred on October 18. This is 5 days later than average, resulting in a frost-free period of 170 days. The normal frost-free period is 169 days.
Open pan evaporation from April 1 through October 31 totaled 69.11 inches, compared to 73.76 inches in an average year. The mean wind speed was 5.6 mph, with 5.5 mph being the average.
The 1996 weather is summarized in the table below. Total precipitation for 1996 was 19.25 inches. Although this is similar to the 30-year average of 17.91 inches, the precipitation distribution was far from normal. Moisture for the 7-month period of October '95 -April '96 totaled only 2.35 inches. This was the driest winter-spring since 1964. May through September proved to be the opposite extreme with precipitation totaling 16.45 inches. This is 4.12 inches above the 30-year average for this 5-month period. August was the wettest month with 4.31 inches, and December was the driest with 0.00 inches, neither of which were records. Snowfall was light, measuring 5.3 inches, or 12.4 inches below normal. Only the months of January, February, and March received measurable snowfall in 1996.
July was the warmest month, with an average temperature of 75.5º and an average high temperature of 88.7º. January was the coldest, with a mean temperature of 28.0º and a mean low temperature of 11.9º. Monthly mean temperatures for 1996 did not deviate appreciably from the 30-year average.
Daily minimum temperatures below zero were recorded on 15 occasions, with the coldest being -10º, Latest and earliest freezes recorded at 32° F. Average precipitation is a 30-year average ) calculated from National Weather Service. Average temperature, latest freeze, earliest freeze, wind, and evaporation are for the same period calculated from station data. Precipitation for 1996 totaled 21.88 inches, which is 5.92 inches above normal. Precipitation was above normal in 6 months. The wettest months were May, June, July, August, and September with 4.05 inches, 2.82 inches, 4.43 inches, 4.67 inches, and 3.77 inches, respectively. October was the driest month with only a trace reported on the 29th. The largest single amount of precipitation was 2.33 inches on May 26, and the greatest single amount of snowfall was 3.0 inches reported on February 2 and April 14. The greatest monthly amount of snowfall, 4.0 inches, was received in January. Snowfall for the year totaled 18.2 inches, with a total of 20 days of snow cover. The longest consecutive period of snow cover, 5 days, was from February 1 to 5.
The air temperature was above normal for only 4 months of the year, with July being the warmest month with a mean temperature of 74.4 o and an average high temperature of 88.9 o . The coldest month was January, with a mean temperature of 27.0 o , an average high of 44.9 o , and an average low of 9.1 o . Nine record high temperatures were set: January 2, 3, and 14; March 21; May 15, 16, and 19; and December 10 and 31. Record low temperatures were set on February 3 and 4 and March 8 and 25. A difference of 100 o occurred within a 7-day period when a record low of -23 o was recorded on February 3 and a record high of 77 o was tied on February 10.
Deviation from the normal was greatest in March, when the mean temperature was 5.8 o below normal. There were 4 days of 100 o or above, compared to the 30-year average of 10 days, and there were 45 days of 90 o temperature and above compared to the 30-year average of 63 days. The lowest temperature for the year was -23 o on February 3 and the highest was 106 o on July 5. The last day of 32 o or less in the spring was on April 30 which is 3 days earlier than the normal date, and the first day of 32 o or less in the fall was October 3, which is the normal date. The frost-free period was 156 days, which is 3 days more than the normal of 153 days.
Open pan evaporation from April through September totaled 59.09 inches, which was 12.58 inches below normal. Wind speed for the same period averaged 4.8 mph, which is 0.9 mph less than normal.

INTRODUCTION
Dryland soybean is seldom grown in southwest Kansas because of lack of drought tolerance. More acres of dryland sunflower are grown, but acreage is far below that of dryland grain sorghum and particularly dryland wheat. Neither crop produces as much residue as grain sorghum or wheat, and the residue decomposes faster. Reduced and no-tillage may allow these crops to be grown, but suitable herbicides are limited.

PROCEDURES
Dryland soybean and sunflower were grown in the wheat-soybean-fallow and wheat-sunflower-fallow cropping systems, respectively, from 1992 through 1996. Conventional-, reduced-, and no-till treatments were compared. Conventional tillage consisted of use of the sweep plow as necessary for weed control during fallow. Weed control in reduced tillage consisted of postemergence herbicides applied as needed between wheat harvest and winter freeze-up followed by sweep tillage in the spring prior to planting. No-tillage consisted of the use of postemergence herbicides for weed control during the entire fallow period. Postemergence herbicides were used because there are very few satisfactory labeled residual herbicides that do not require incorporation. Cargill SF100 sunflower and Olde 3431 soybean were planted in late May to early June at rates of 18000 plants/acre and 60 lbs/acre, respectively.

RESULTS AND DISCUSSION
Yields are presented in Table 1. Climatic conditions during the 1992-1996 growing seasons were much more favorable than normal, and except for 1994, resulted in soybean yields higher than can usually be expected. Well distributed, above-average rainfall in 1996 resulted in yields exceeding 40 bu/ acre. At the yield levels in this study, and considering price, soybean was probably competitive with grain sorghum. However, soybean does not produce enough residue to prevent erosion, and even with the straw remaining from the previous wheat crop, may not meet conservation compliance requirements. However, dryland soybean could be used in special situations such as the corners remaining in centerpivot irrigated beans. Sunflower produced good yields, and with proper management of the stalks during fallow, can meet conservation compliance requirements in most years, particularly with reducedor no-till.  Crop 1992Crop 1993Crop 1994Crop 1995Crop 1996  Within a crop, means in a column followed by a different letter differ at the 0.10 probability level.
No-till often improved the yield of both crops. However, no-till is probably not practical for either crop, because of the absence of suitable labeled herbicides. The use of reduced-, rather than notillage, may make dryland soybean and sunflower practical. More research is needed.

SAFFLOWER, AN ALTERNATIVE DRYLAND CROP FOR WESTERN KANSAS
by Curtis Thompson,Alan Schlegel,and Neil Riveland 1 INTRODUCTION Safflower is an annual broadleaf crop that may be grown as an alternative crop in western Kansas. Safflower is grown for it seed, which is crushed for edible oil or used whole in the bird seed industry. This deep-rooted crop appears to have similar yield potential to sunflower but has better drought tolerance, is bird resistant, and has fewer problems with insects. Safflower can have significant disease problems, especially when grown in areas with high precipitation and humidity; thus, its adaptability would likely decrease in central or eastern Kansas. For these reasons, Tribune was selected as a site to evaluate safflower as a potential crop in western Kansas.

PROCEDURES
Safflower varieties were planted on March 3, 1994;March 28, 1995;and April 16, 1996. Treflan at 1.5 pints/acre was applied and incorporated prior to planting safflower in 1994 and '95. No preemergence herbicide was used in 1996. Safflower was planted with a hoe-drill in 10-inch rows approximately 1 inch

K STATE
Southwest Research-Extension Center deep. Poor emergence can result from planting safflower too deep. Safflower were planted at 350,000 pure live seed (PLS) in 1994, and200,000 to 250,000 PLS in 1995 and'96. The recommended seeding rate for safflower is 15 to 25 pounds per acre, which is similar to the 1995 and '96 planting rates. All safflower experiments were planted on fallow in a wheat fallow system. Plot size was 5 by 35 or 40 feet. Safflower was harvested on August 12, 28, and 29 in 1994, '95, and '96, respectively. RESULTS AND DISCUSSION Twenty six to 33 lb seeding rates were used with the early March planting in 1994 (Table 1). Safflower had good tolerance to cold temperatures early; however, the early planting didn't appear to enhance safflower yield. Plant densities were too thick and little branching occurred. More normal seeding rates were used in 1995 and '96 with the late March and April seedings (Table 1).
Safflower planted in early March began flowering during the third week of June approximately 16 weeks after planting (Table 1). Safflower planted in mid April began flowering in early July approximately 11+ weeks after planting. Safflower is typically a 120-day crop; however, very early planting dates will extend the growing period.
Safflower yields during the 3-year period ranged from 550 to 2149 lb/acre ( Table 2). The variety Girard had a very poor year in 1994 and was dropped from testing. Centennial, Montola, S208, and S541 have been the best yielding varieties in the trial over the 3-year period. Safflower yields were similar to yields of sunflower in the area; however, the early planted safflower in 1994 may have been lower yielding than sunflowers. This study was not designed to make an actual yield comparison with sunflowers.
Further testing should be conducted on safflower planting dates and also to evaluate a wheat-safflowerfallow rotation or perhaps a wheat-sorghum-safflowerfallow rotation. Safflower should not be used in rotation with sunflower.
Safflower plant height ranged from 25 to 35 inches (Table 3). Height was affected by variety and appeared to vary among years; however, planting dates varied in each of the three years. Very early planting dates may lead to shorter plants. Test weights ranged from 37.3 to 45.2 lb/bu. Good safflower seed should weigh from 42 to 45 lb/bu.

INTRODUCTION
The WSF cropping system is superior to wheatfallow (WF) in terms of yield and profitability. In the northwest Kansas, southwest Nebraska, northeast Colorado region, corn often is substituted for sorghum in a WCF rotation. Dryland corn is perceived to lack sufficient drought and heat tolerance for southwest Kansas. However, interest in dryland corn is increasing, and the wheat-corn-fallow system may be feasible using modern corn hybrids and production practices. Therefore, a study was conducted to compare the yield and profitability of the WSF and WCF cropping systems.

PROCEDURES
The WSF and WCF cropping systems were compared from 1992 through 1995. Conventional -(CT), reduced-(RT), and no-till (NT) treatments were compared. The CT, RT, and NT treatments were applied to both crops in the rotation. Because wheat usually has not responded to a reduction in tillage, a conventional-till wheat, no-till corn or sorghum treatment (CNT) was included to reduce herbicide expense and increase profitability. Herbicide and

A COMPARISON OF THE WHEAT-SORGHUM-FALLOW AND WHEAT-CORN-FALLOW CROPPING SYSTEMS
by Charles Norwood tillage operations used by farmers for these cropping systems will vary depending on factors such as rainfall and weed pressure. The treatments used in this particular study are listed below.
WHEAT-SORGHUM OR CORN-FALLOW (PRIOR TO  WHEAT) CT and CNT -Four tillage operations. RT -2.4 lb/acre cyanazine in the spring followed by two tillage operations.
WHEAT-CORN-FALLOW (PRIOR TO CORN) CT -Two tillage operations after wheat harvest followed by one preplant tillage operation and a preplant application of 1.0 lb/acre atrazine + 1.5 lb/ acre metolachlor.
WHEAT-SORGHUM-FALLOW (PRIOR TO SORGHUM) CT -Two tillage operations after wheat harvest followed by two tillage operations before planting and a preplant application of 1.0 lb/acre atrazine + 1.5 lb/acre metolachlor.
NT and CNT -2.0 lbs/acre atrazine + 0.75 lb/ acre glyphosate + 1.0 lb/acre 2,4-D after wheat harvest followed by 1.6 lb/acre cyanazine about 30 days prior to planting. 1992 and 1995, corn yielded more than sorghum regardless of tillage treatment. This occurred because corn has a higher yield potential, and favorable climatic conditions during the study period allowed that yield potential to be expressed. The highest corn yields of the 4-yr period occurred in 1992, because of aboveaverage, well-distributed rainfall and cooler than normal temperatures. Little difference occurred in corn yield during the remaining years. Sorghum yields were reduced in 1995 by an early freeze; thus, yields of both sorghum and wheat were reduced by freezes in 1995, an unusual occurrence.
Sorghum yields were not affected consistently by a reduction in tillage. Yields were increased by RT and NT only in 1994. Unlike wheat, sorghum usually responds to a reduction in tillage. This response usually is caused by additional soil water at planting. The no-till sorghum plots had additional soil water at planting only in 1994 and 1995; any potential yield response was negated by the freeze in 1995. Corn yields were increased by both reduced and no tillage in 3 of 4 years. No-tillage did not increase yields above those of reduced tillage, and no-till corn yields were not affected by the tillage system used prior to the previous wheat crop (CT or NT). Corn responded to the reduction in tillage more often than did sorghum because of additional soil water at planting and the higher water-use-efficiency of corn.
Budgets. Combined costs for wheat and sorghum or corn are presented in Table 3. These costs would be incurred over a 3-year period or more likely in one and one-half years, if the acreage is divided into thirds so that both wheat and corn or sorghum are produced each year. Total costs increased as tillage was reduced. However, a significant amount of this cost increase was negated by use of the CNT system. Compared to CT in the WSF system, NT was $32.43 more expensive, but CT wheat and NT sorghum (CNT) cost only $17.07 more than an all-CT system. For the same comparisons in WCF, the figures were $42.66 and $29.84. Thus, savings of $15.36 and $12.82 for the 2 acres were obtained for WSF and WCF, respectively, by using CNT rather than an all-NT system. These cost reductions were due mainly to lower herbicide and fertilizer costs for the CT wheat in the CNT system. Whereas variable costs were lower for the CNT system compared to the all-NT system, fixed costs were higher because machinery was retained. A close inspection of Table 3 reveals that machinery costs (depreciation, interest, and insurance) were $17.94 higher for CNT compared to the all NT system. This was because tillage equipment was needed for the CT wheat phase of the rotation.
Thus for WSF and WCF, prior to wheat, one herbicide application in RT replaced two tillage operations, or one-half the tillage. Three herbicide applications in NT replaced all tillage. For WSF and WCF, prior to corn or sorghum, one herbicide application in RT replaced two tillage operations, or the tillage that otherwise would occur in the summer and fall following wheat harvest. Two herbicide applications in NT replaced all tillage.
Tillage was performed with a sweep plow. The wheat and row crops were fertilized with 40 and 80 lb N/acre, respectively. The N source was anhydrous ammonia for all treatments except NT which received UAN. Planting dates for corn were between May 13 and 17, whereas sorghum planting dates varied between May 20 and June 12. Wheat was planted between September 13 and September 21. Seeding rate for wheat was 60 lbs/acre, whereas the sorghum plant population was about 25,000 plants /acre. The target plant population for corn was 18,000 plants/ acre, but varied from about 12,700 in 1992 to 16,700 in 1995. The reduction in emergence was due to either dry surface soil at planting or crusting after rainfall. 'Warner 744BR' grain sorghum, 'ICI 8714' (105 day maturity) corn, and 'TAM 107' winter wheat were planted each year.
An enterprise budget was developed for each cropping system following the guidelines in a Kansas State University Farm Management Guide (MF-904, 1996). The variable costs for labor, fuel, and repairs and the fixed machinery costs were based on individual machinery sets for each system. Assumptions were based on a 2,000 acre farm, all of which is owned.

RESULTS AND DISCUSSION
Yields. Wheat yields were highest in 1994 because of above-average growing-season rainfall but were reduced in 1995 because of a late-spring freeze (Table  1). Wheat yields were not affected by cropping system or tillage in any year. The lack of a wheat yield response to a reduction in tillage is not inconsistent with other studies at Garden City. In western Kansas, spring rains tend to even out soil water differences at planting, eliminating potential yield differences in wheat.
Corn usually yielded more than grain sorghum (Table 2). In 1993, CT sorghum yielded more than CT corn, but the use of reduced or no tillage resulted in corn yields equaling or exceeding sorghum yields. In 1994, CT corn yields were not statistically different from CT sorghum yields, but RT and NT corn yields were higher than the respective sorghum yields. In   Returns. Because it takes 3 years to complete one cycle of WSF or WCF, the sums of the wheat and row crop returns were divided by three and expressed as $/acre/year in Table 4. Differences in return between the WCF and WSF systems were influenced mainly by the returns of corn and sorghum, because wheat yields and returns were not affected by cropping system. The WCF system returned significantly more than WSF in 12 of the 16 year x tillage comparisons because of higher yield and return from corn. More income was produced by WSF in only one year x tillage combination, that being CT in 1993. On average, the WCF system produced $7.80, $17.10, $13.55, and $19.87 more income than WSF for the CT, RT, NT, and CNT treatments, respectively. Returns in 1995 were negative from WSF and near zero from WCF, because the freeze reduced wheat and sorghum yields.
No-till returns in WCF did not differ from CT returns in 1993, 1994, and 1995, but were less than CT in 1992. Thus, the response of corn to NT usually compensated for the lack of response of wheat to NT (and the corresponding lower returns of NT wheat) and resulted in no statistical differences between CT and NT returns of WCF in 3 of 4 years. Reduced-CT and CNT in 1992and 1993and CT and RT in 1995 Tillage had no effect on WSF returns in 1994.
Considering income for the 4 years, CNT in WCF produced $24.68, $27.48, and $42.40/acre more than CT, RT, and NT, respectively. The CNT system in WSF produced $16.44/acre more than RT and $17.12/acre more than NT, but $23.60/acre less than CT. Thus, the CNT system was more profitable in WCF than in WSF. In contrast to previous studies, the CT system produced the most income in WSF because of the lack of response of sorghum to NT during this particular period of time.
tillage returns were never greater than CT returns and were less than CT returns in 1992. Reduced-tillage returns were higher than NT returns in 1995. The CNT treatment in WCF had statistically higher returns than NT in 1992and 1993, RT in 1992, and CT in 1993and 1994. The CNT treatment never had statistically lower returns than any other treatment. Thus, CNT was among the best treatments in all years and returned more than all other WCF treatments averaged over 4-yr.
Returns from the CNT system in WSF were never higher than CT and were lower than CT in 1995. The most profitable treatments in WSF were

SUMMARY
Corn yields from one, two, and three irrigations were 121%,129%,and 148% more, respectively, than dryland yields. Gross income averaged $315/acre when all acres were dryland. When all acres were irrigated once, gross income (less the cost of the irrigation water) was $372/acre. When one-half the acres were dryland and one-half were irrigated twice, gross income was $351/acre. When two-thirds of the acres were dryland and one-third was irrigated three times, gross income was $356/acre. Thus, during the time period of this study, irrigating all acres one time was the most profitable practice.

INTRODUCTION
Many producers are limiting irrigation because of the decline of the Ogallala aquifer and increasing energy costs. A reduction in irrigated area is expected to result in an increase in dryland cropping systems such as wheat-fallow and wheat-sorghum-fallow. Dryland crops produce only one-third to one-half the yield of irrigated crops. To slow the transition from irrigated to dryland acres, cropping systems that efficiently use both precipitation and irrigation water need to be developed. Continued irrigation, even if very limited, will allow the use of expensive irrigation systems already in place and, more importantly, will stabilize grain production in areas that otherwise would be returned to dryland. Therefore, a study was designed with the objective of determining whether it is more profitable to irrigate a large acreage fewer times or a smaller acreage more times.

PROCEDURES
Dryland corn was compared with corn irrigated one, two, or three times. Each irrigation consisted of 4 inches of water. When corn was irrigated once, the irrigation was at tassel; when irrigated twice, at tassel and grain fill; and when irrigated three times, at vegetative, tassel, and grain fill. The cropping system used for all treatments was the wheat-corn-fallow system, which has 10-to 11-month fallow periods prior to each crop. The fallow period was used to store water and made pre-irrigation unnecessary. Conventional tillage (CT) and no-tillage (NT) treatments were compared. Herbicides in the NT plots consisted of 2 lb/acre atrazine applied after wheat harvest followed by 1 lb/acre atrazine plus either 1.6 lb/acre Bladex or 2 lb/acre Dual applied as a tank mix shortly before planting. The CT plots received the same preplant herbicides, but sweep tillage was used for weed control during fallow instead of atrazine.

RESULTS AND DISCUSSION
Corn yield increased with irrigation, as expected (Table 1). However responses to the different irrigations were not linear. Average responses to one, two, and three irrigations were 12, 8, and 20 bu/acre, respectively. Response to two irrigations was less, and response to three irrigations was more than expected. Corn responded to NT in 2 of 3 years, and average yield increased 14 bu/acre. The figures in Table 2 are gross income less the cost of irrigation water at $2.25/inch. These results should be considered preliminary, because climatic conditions during the study period were more favorable than usually can be expected. However, based on 3 years of results, the most income occurred when all acres were irrigated one time, whereas irrigating a reduced acreage more times produced less income. This particular experiment was flood irrigated; however, the results also can be applied to sprinkler irrigation. What the results do not illustrate is the importance of timeliness. A farmer with a low capacity well may not be able to flood irrigate all acres in a timely manner, i.e., when the crop is in the proper growth stage, whereas a farmer with a sprinkler can Means in a column or row within a year followed by a different letter differ at the 0.05 probability level.
adjusted so that the corn is irrigated prior to pollination. Any additional irrigations, up to the maximum economic return, should be considered a bonus.
probably irrigate his acres faster. With limited water, the most important irrigation is the one at pollination; therefore, the amount of irrigated acres should be

TILLAGE AND NITROGEN EFFECTS ON DRYLAND CROP PRODUCTION
by Alan Schlegel, David Frickel, and Curtis Thompson

SUMMARY
Tillage system had no effect on wheat yields in any year from 1993-96. Grain sorghum yields in 2 of 4 years were greater with reduced-than no-till, primarily because of increased grassy weed problems in no-till. Production costs were less with reducedthan no-tillage. Grain yields were increased 64 to 90% by N fertilization. Fertilizer N requirements were greater than 50 lb N/acre for both crops. Fertilization of the previous crop increased yield of the subsequent crop up to 33%. Nitrogen applications tended to increase fallow efficiency. Available soil water at planting was not affected by N rate or tillage.

INTRODUCTION
The principal dryland crop in the central Great Plains is winter wheat grown in a wheat-fallow system. However, producers are changing to more intensive cropping systems, such as wheat-sorghum-fallow, because of the potential for increased profitability. To be feasible, reduced-or no-tillage practices must be used in these intensive cropping systems to better utilize limited precipitation and maintain crop productivity. Nitrogen fertilizer is applied routinely to dryland crops in this region to optimize grain yields. This study was conducted to 1.) quantify wheat and grain sorghum responses to N fertilization in a wheat-sorghum-fallow rotation under reducedand no-tillage systems, 2.) determine the residual effect of N fertilization on subsequent crops, and 3.) determine the effect of tillage practices on N response.

PROCEDURE
This research was initiated in 1991 in west-central Kansas at the Southwest Research-Extension Center near Tribune, KS. The study was located on a Richfield silt loam soil with a pH of 7.5 and organic matter of 1.5%. The experimental design was a split plot with tillage as main plots and N treatments as subplots. The two tillage systems were reduced (RT) and no tillage (NT). The RT system utilized a combination of herbicides and tillage for weed control during fallow, whereas NT relied solely on herbicides. A generalized weed control program for each system is outlined in Table 1. A blade plow (sweep) was used for all tillage operations, which is typical for this region. Weed control costs were about 20% greater with no-till than reduced tillage. The N treatments were 25, 50, and 100 lb N/acre applied to either wheat or grain sorghum and 25 and 50 lb N/acre applied to both crops along with an untreated control. Nitrogen fertilizer as urea was surface broadcast in the early spring on growing wheat and near planting time of grain sorghum. Phosphorus fertilizer (100 lb P 2 O 5 / acre) was applied at wheat planting to maintain adequate soil P levels. Plot size was 20 by 60 ft. The center of each plot was machine harvested, and grain yields were adjusted to 12.5% moisture.
Grain yields reported are averaged across 1993-96. Soil water to a depth of 8 ft was measured at planting and harvest in three N treatments (25 and 50 lb N/acre applied to both crops and the control) in both tillage systems. Along with precipitation records, this allowed calculation of crop water use, soil water accumulation during fallow, and fallow efficiency. Precipitation during the study period was 20% greater than the normal of 16 inch/yr. Residual soil N content at the start of the study was less than 10 ppm N (nitrate plus ammonia in a 2-ft profile).

RESULTS AND DISCUSSION
Nitrogen fertilization increased wheat yields up to 90% or 26 bu/acre ( Table 2). Application of 50 lb N/acre was not sufficient to maximize yields, because wheat yields were 9 bu/acre greater with 100 than with 50 lb N/acre. Nitrogen applied to the previous and 1996, sorghum yields were greater with reduced tillage than with no-tillage. Grassy weeds (especially witchgrass and sand dropseed) caused severe problems in 1996, particularly in no-till, which greatly reduced grain yield. In general, weed control costs were greater with no-till than reduced tillage (Table 1). Nitrogen applications tended to increase crop water use, decrease soil water at harvest, and increase fallow efficiency (Tables 4 and 5). This corresponds to increased residue production in the fertilized treatments (data not shown). Tillage had little effect on residue production and generally little effect on soil water storage or use. However, for both crops, more soil water was available deeper in the profile with no-till than with reduced tillage (data not shown). sorghum crop had a positive residual effect on subsequent wheat yield. For example, when sorghum received 100 lb N/acre, wheat yields were 10 bu/acre greater than those of the control. Tillage had no effect on wheat yield, and no N x tillage interaction occurred.
Grain sorghum yields were increased up to 64% or 23 bu/acre by 100 lb N/acre applied to sorghum (Table 3). Again, N requirements were greater than 50 lb N/acre because sorghum yields were 6 bu/acre greater with 100 than with 50 lb N/acre. The residual effect of fertilizer N applied to wheat increased sorghum yields up to 12 bu/acre. Averaged across the 4 years, tillage had little effect on grain yield, and no N x tillage interaction occurred. However, in 2 years the effect of tillage was significant. In 1993

LONG-TERM FERTILIZATION OF IRRIGATED CORN by Alan Schlegel
SUMMARY Long-term research shows that phosphorus (P) and nitrogen (N) fertilizers must be applied for optimum grain yields of irrigated corn in western Kansas. In this study, N and P fertilization increased corn yields more than 100 bu/acre. Application of 160 lb N/acre tended to be sufficient to maximize corn yields. Phosphorus increased corn yields by 75 bu/acre when applied with at least 120 lb N/acre. Application of 40 lb P 2 O 5 /acre was adequate and higher rates were not necessary.

INTRODUCTION
This study was initiated in 1961 to determine responses of continuous corn grown under flood irrigation to N, P, and potassium (K) fertilization. The study is conducted on a Ulysses silt loam soil with an inherently high K content. No yield benefit to K fertilization was observed in 30 years and soil K levels remained high, so the K treatment was discontinued in 1992. However, a yield increase from P fertilization has been observed since 1965, and we were concerned that the level of P fertilization might not be adequate. So, beginning in 1992, a higher P rate was added to the study and replaced the K treatment.

PROCEDURE
Initial fertilizer treatments in 1961 were N rates of 0, 40, 80, 120, 160, and 200 lb N/acre without P and K; with 40 lb P 2 O 5 /acre and zero K; and with 40 lb P 2 O 5 /acre and 40 lb K 2 O/acre. In 1992, the treatments were changed with the K variable being replaced by a higher rate of P (80 lb P 2 O 5 /acre). All fertilizers were broadcast by hand in the spring prior to planting and incorporated. The corn hybrid was Pioneer 3379 (1992-94) and Pioneer 3225  planted at 32,000 seeds/acre in late April or early May. All plots were furrow irrigated to minimize water stress. The center two rows of all plots were machine harvested after physiological maturity. Grain yields were adjusted to 15.5% moisture.

RESULTS AND DISCUSSION
Nitrogen and P fertilization increased corn yields averaged across the 5-year period by over 100 bu/ acre. In 1995, hail during the growing season reduced overall yields about 40%, but yields still were increased up to 80 bu/acre by N and P fertilization. The apparent N fertilizer requirement was about 160 lb/acre. Application of 40 lb P 2 O 5 /acre increased yields about 75 bu/acre when applied with at least 120 lb N/acre. A higher rate of P was not necessary, because no significant yield difference occurred for applications of 40 and 80 lb P 2 O 5 /acre. retirement program, the "Soil Bank", most acres planted to grass will return to crop production. The southwest and west-central Kansas crop reporting districts have almost 1.2 million acres enrolled in the CRP (over 40% of the Kansas total). The principal crop grown on land prior to enrollment in the CRP was winter wheat. With the expiration of CRP contracts, the opportunity exists to initiate alternative cropping systems that include crops other than winter wheat. These systems may be more productive and profitable than wheat-fallow systems and can reduce soil erosion and better sustain soil quality.

PROCEDURES
This study was initiated in the spring of 1995 in west-central Kansas near Tribune, KS. The study area was enrolled in the CRP and had an established stand of warm-season grasses. Primary species were sideoats grama, little bluestem, blue grama, buffalograss, and switchgrass, which are typical for the area. Soil type was a Richfield silt loam with less than 1% slope. The objectives of the project were to determine best management practices for returning CRP land to crop production. The variables evaluated were residue treatment (burn, mow, or leave standing); grass control method (tillage or chemical control); and initial crop selection. The site was divided into four areas for planting of grain sorghum in the springs of 1995 and 1996 and winter wheat in the falls of 1995 and 1996. The burn treatments were done on all four areas in late April 1995. The mow treatments were done in early May 1995 for the 1995 plantings and early July 1996 for the 1996 plantings. The area to be planted to wheat in fall 1996 was mowed again in late September 1995.
Treatments for 1995 grain sorghum were combinations of residue treatment (burn, mow, or leave standing) and grass control method (tillage or chemical). The tillage treatment consisted of two SUMMARY The majority of the CRP acres in Kansas are in western Kansas. Most contracts under the initial CRP are about to expire. If these acres are not reenrolled in the new CRP program, most of the land is expected to be returned to crop production. This study was initiated in 1995 to evaluate best management practices for returning CRP land to crop production. The CRP grasses (mixed species, warmseason grasses) were controlled better by tillage than herbicides, and good grass control is essential for optimum crop production. Removal of the old residue by burning may be beneficial. Soil water content is very low following destruction of the CRP grasses. Sufficient time should be allowed between destruction of the CRP grasses and planting of the first crop to allow accumulation of soil water. Residual soil inorganic N levels are extremely low in CRP land and supplemental N fertilization (possibly greater than normal amounts) will be required for optimal growth of the initial crop.

INTRODUCTION
In Kansas, 2.9 million acres were enrolled in the Conservation Reserve Program (CRP), which was the third greatest participation by any state. The majority (>50%) of the CRP acres in Kansas are in the western one-third of the state. Hamilton County had the highest CRP, enrollment of over 125,000 acres. Stanton, Morton, and Greeley counties each had over 80,000 acres. Most contracts under the initial CRP are about to expire. The new Farm Bill re-authorized the CRP, and some of the land currently enrolled in CRP will be enrolled again. However, some of the CRP land will not be eligible for reenrollment, and some land will not be rebid. Over 90% of the CRP land in Kansas is planted to grass. Based on past experience with an earlier land

Southwest Research-Extension Center
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. offset disk operations in mid-June. The chemical grass control treatment consisted of applications of glyphosate (1 qt/acre) plus ammonium sulfate and surfactant in early June and repeated in late June. Grain sorghum was planted in late June. Atrazine (0.75 lb/acre) and Dual (1 qt/acre) were applied to all treatments.
The area for 1995-96 winter wheat had identical residue treatment as described for 1995 sorghum. For the plots using tillage only for grass control, they were offset disked in mid-June, early July, and mid-August followed by a sweep plow operation in mid-September. For grass control using only herbicides (no-till), glyphosate (plus ammonium sulfate and surfactant) was applied in early June (1 qt/acre), late June (1 qt/acre), and late September (2 qt/acre). Other treatments consisted of a mixture of tillage and herbicides for grass control. Winter wheat was planted in late September.
In preparation for planting sorghum in 1996, residue was burned in late April 1995 and mowed in early July 1995. The tilled plots were offset disked in early July and mid-August 1995 followed by a sweep plow in mid-September 1995 and early-June 1996 immediately prior to sorghum planting. The no-till plots received glyphosate (2 qt/acre) in mid-July and again in late-September 1995 followed by glyphosate and 2,4-D (Landmaster BW at 40 oz/acre) in early June 1996 prior to sorghum planting. Reduced-till treatments combined one application of glyphosate (2 qt/acre) either in July or September 1995 with several tillage operations. The reduced-tillage treatment that received glyphosate in July was offset disked in August and sweep plowed in September 1995. The other reduced tillage treatment was offset disked in July 1995 and treated with glyphosate in September 1995. Both reduced-tillage treatments were tilled (sweep plow) prior to sorghum planting on June 11, 1996. Atrazine (0.75 lb/acre) was applied on June 19 to all treatments.
The no-till treatment for 1996-97 wheat received three applications of glyphosate (2 qt/acre) plus ammonium sulfate and surfactant (mid-July 1995, early July 1996, and late August 1996). The conventional-tillage treatment was offset disked twice (July and August 1995) and sweep plowed four times (September 1995, June, July, andSeptember 1996). Reduced tillage treatments received one application of glyphosate (2 qt/acre) plus ammonium sulfate and surfactant either in July or September 1995. The reduced-tillage treatment that received glyphosate in July was offset disked in August 1995 and sweep plowed in September 1995. The other reduced-tillage treatment was offset disked in July 1995. Both reduced-tillage treatments were sweep plowed three times in 1996 (June, July, and September). Winter wheat was planted on September 13, 1996 with starter fertilizer (100 lb/acre of 11-52-0 applied with the seed). Stand establishment was adequate in all treatments. Fertilizer N was applied in December at rates of 50, 100, and 150 lb N/acre.

RESULTS AND DISCUSSION
Sorghum growth in 1995 was hampered severely by lack of soil moisture, and no crop was harvested. Chemical grass control was better following residue burning than other residue treatments but was not adequate with any no-till treatment. This area was planted to sorghum again in 1996. Grain yields were very low in all treatments (Table 1). For 1995 sorghum, LSD calculated using only burn and mow treatments. LS = residue was left standing.
For 1996 wheat, June 1995 applications of glyphosate were unsuccessful in controlling the warmseason grasses. The glyphosate treatment in September increased grass control to about 75% (primarily sideoats grama). Generally, all disk treatments provided acceptable control of the grasses. Soil inorganic N levels at wheat planting were very low. Soil nitrate was about 2 ppm in the surface foot and less than 1 ppm in the 2 through 6 ft depth. Initial stand establishment was much better in the tilled plots than in no-till. However, the wheat was killed by dry winter conditions and spring freezes. This area was planted to sorghum in June 1996. Sorghum yields ranged from 6 to 32 bu/acre and were greatest in the tilled treatments and least with no-till (Table 1). With reduced tillage, yields were greater when the initial operation was tillage rather than a chemical application. The residue treatment had little effect on sorghum yield.
For the 1996 grain sorghum area, yields were greatest in the conventional-tillage treatments and least in the no-till treatments (Table 1). Yields in the tilled treatments tended to be slightly greater when the residue had been burned rather than mowed or left standing. In general, grain yields were disappointingly low, possibly because of inadequate N availability. Evaluation of fertilizer N needs will be made in the 1997 wheat crop.
Grass control ratings were taken in early September 1996 prior to planting of winter wheat . The warm-season grasses were eliminated by conventional tillage and 90% controlled in no-till. With reduced tillage, grass control was 90% when the residue had been burned but only about 70% when the residue had been mowed. An evaluation in spring of 1997 will provide better information on long-term control.
Observations from this study are: 1.) the mixed species, warm-season grasses established on CRP land in western Kansas are difficult to control with herbicides alone; 2.) burning of the residue may be beneficial; 3.) crop establishment and growth will be difficult without good grass control; 4.) some tillage may be required to ensure adequate control of the CRP grasses; 5.) soil water is depleted by the CRP grasses, and a fallow period to store soil water will be necessary prior to crop planting; and 6.) residual soil inorganic N levels are extremely low, and supplemental N fertilization will be required (likely in excess of typical N rates).

WATER-USE EFFICIENCY OF FULL-SEASON AND
SHORT-SEASON CORN 1 by Todd Trooien, Larry Buschman, Phil Sloderbeck, Kevin Dhuyvetter 2 , William Spurgeon 3 , and Dennis Tomsicek greater or lesser for short-season corn compared to full-season corn.
The objective of this study was to compare the water-use efficiency of short-season corn to that of full-season corn. PROCEDURES This experiment was conducted in southwest Kansas under a modified center pivot fitted with lowpressure in-canopy nozzles operated in the spray mode. The four-factor experiment was arranged in a randomized complete block design with four replications. Treatments were (1) three crops (fullseason corn, short-season corn, and medium-season grain sorghum); (2) two planting dates (early and late, presented in Table 1); and (3) two irrigation amounts (fully irrigated and limited irrigation). Maturity ratings were 118 days for the full-season corn (Pioneer 3162) and 97 days for the short-season corn (Pioneer 3751). The grain sorghum hybrid used was DK-56. Grain sorghum was not grown in 1996. The irrigation treatments were full replacement of the base irrigation requirement (1.0 BI, the calculated ET minus received rainfall) and 0.70 BI for the limited irrigation. Crop ET for irrigation scheduling was calculated with an alfalfa-based, modified Penman equation.
Weather variables were measured with the Southwest Research-Extension Center automated weather station, about a mile from the experiment site. Precipitation was measured at the experiment site. Soil water content was monitored approximately weekly with a neutron attenuation moisture meter. Total crop water use was the sum of irrigation, precipitation, and the soil water depletion during the SUMMARY Short-season corn, full-season corn, and grain sorghum were grown and irrigated for 4 years to compare their water-use efficiency. Full-season corn yields (in bu/acre) were greater than short-season corn yields, which were greater than grain sorghum yields. Fully irrigated yields were greater than yields under limited irrigation (replacing 70% of crop evapotranspiration, or ET). Full-season corn used the greatest amount of water from emergence to maturity. Water-use efficiency was greatest for full-season corn for 2 of the 4 years but was greatest for short-season corn in the other 2 years. In summary, the results indicate no justification for choosing short-season corn over full-season corn based solely on water-use efficiency.

INTRODUCTION
Corn is often the most profitable crop choice for fully irrigated production in southwest Kansas. However, if well capacities decrease and energy prices increase, full irrigation can become impractical or impossible in some cases. Crop production alternatives are being sought to reduce the amount of irrigation water required.
One potential crop is short-season corn. Among other things, short-season corn matures more quickly and, as a result, uses less water. But the yield potential of short-season corn is less than that of full-season corn, so full-season corn has an advantage in highrainfall years because of its greater yield potential. Also, we do not know if the water-use efficiency (grain yield per inch of water used by the crop) is

RESULTS AND DISCUSSION
Grain yields of full-season corn were equal to or greater than grain yields of short-season corn except for the late planting in 1995 (Table 2). For corn, limited irrigation always resulted in reduced yields. Yields of short-season corn were greater than yields of grain sorghum in our experiment for both limited and full irrigation. For the grain sorghum, limitedirrigated yields were equal to or greater than fully irrigated yields in 1993 and 1995.
The water-use values (Table 3) reflect the fact that seasonal ET was less than the long-term average for all 4 years of this study. When compared within a planting date, seasonal water use by the full-season corn was greater than water use by short-season corn. Water use by grain sorghum was comparable to that of short-season corn in 1993 and 1994. In 1995, stress reduced water use and yield of grain sorghum, especially for the late planting.
The water-use efficiency of short-season corn was not consistently greater than that of full-season corn (Table 4). In 1993 and 1996, water-use efficiency of full-season corn was actually equal to or greater than that of short-season corn, except for the lateplanted, fully irrigated corn in 1993. In 1994 and 1995, however, water-use efficiency of short-season corn was equal to or greater than that of full-season corn, again with one exception (early-planted, fully irrigated corn in 1995). The water-use efficiency for corn was always equal to or greater than that for grain sorghum except for early-planted, limited-irrigated grain sorghum that had high yield and low water use in 1995.
In conclusion, the water-use efficiency of shortseason corn was not consistently greater than the water-use efficiency for full-season corn. Therefore, when making cropping decisions, short-season corn should not be selected over full-season corn solely on the basis of water-use efficiency.

SUMMARY
Corn is the primary grain crop for irrigators in western Kansas. However, many irrigation systems have insufficient well capacities to obtain maximum corn yields. This study evaluated the effects of limited well capacity and seeding rate on corn production. Growing-season precipitation was above normal in 1996, which greatly reduced irrigation requirements. The lowest well capacity evaluated, 0.10 inch/day, was adequate for maximizing grain yield. Maximum grain yields were obtained with 26,000 seeds/acre. Higher seeding rates were not needed, and lower seeding rates reduced yields about 20 bu/acre.

INTRODUCTION
Corn is the primary grain crop for irrigators in western Kansas. Past research has shown that each acre-inch of irrigation water has the potential to produce 7 to 15 bushels of corn. In some areas, declining water availability has resulted in a significant number of irrigation systems being operated with insufficient well capacity to obtain maximum yields. This research addresses the effect of limited well capacities on corn yield.

PROCEDURES
The study was conducted at the Tribune Unit, Southwest Research-Extension Center near Tribune, KS in 1996 on a Ulysses silt loam soil. The entire study area was irrigated in early spring to minimize soil water differences among treatments at planting. The irrigations were applied in 2.3-inch increments in level flood basins. This amount of irrigation was necessary for uniform water distribution across each plot. The first in-season irrigation was on June 25 for all treatments except the control. The frequency of irrigation was dependent upon the various simulated

K STATE
Southwest Research-Extension Center well capacities, and the interval ranged from about 9 days for the 0.25 inch/day capacity to about 23 days for the 0.10 inch/day capacity. Total in-season irrigations were as follows with the last irrigation on August 29:

Well capacity
In-season irrigation inch/day inches (number of irrigations) 0 0 0.101 6.9 in.
Precipitation from emergence (May 7) through August 31 was 15.61 in. Estimated evapotranspiration (ET) for the same period was 20.99 in. The lowest capacity treatment provided sufficient irrigation to meet ET in 1996.
Corn (Pioneer 3162) was planted on April 21 at three seeding rates (18, 26, and 34 thousand seeds/ acre). An insecticide (Force at 8 lb/acre) was applied at planting. For weed control, Harness Plus (1 qt/ acre) + atrazine (1 lb/acre) was applied preemergence on April 22. Fertilization totaled 210-100-0 applied in split applications. The center two rows of each plot were machine harvested on October 18, and yields were adjusted to 15.5% moisture.

RESULTS AND DISCUSSION
Growing-season precipitation was above normal in 1996, which greatly reduced the need for irrigation. Estimated ET was only about 6 inches greater than precipitation. The lowest well capacity (0.10 inch/ day or 1.9 gpm/acre) supplied about 6.9 inches of irrigation water and was adequate to maximize grain yield (Table 1). To determine the required well capacity for field irrigation systems, the system application efficiency must be taken into account. For example, in a furrow-flood system with 60% application efficiency, the well capacity to supply 0.10 inch/day of applied water would be 500 gpm for 160 acres. For a sprinkler system with 90% efficiency, it would take a 260 gpm well to irrigate 125 acres. The highest irrigation treatment, 0.25 inch/day, would require a 1250 gpm well for the flood system and a 650 gpm well for the sprinkler.
A seeding rate of 26,000 seeds/acre was adequate to produce maximum grain yield at each well capacity. Without irrigation, the highest seeding rate reduced grain yield by about 30 bu/acre. With irrigation, increasing the seeding rate above 26,000 seeds/acre had little effect on grain yield. The lowest seeding rate (18,000 seeds/acre) reduced yield about 20 bu/ acre at all irrigation levels.

SUMMARY
Five different sorghum hybrids treated with Gaucho were monitored to evaluate the seed treatment's impacts on greenbug populations and sorghum yield under both dryland and irrigated conditions. Gaucho was found to reduce greenbug populations by about 99% early in the season (18 days after planting) on 4-to 5-leaf sorghum and by about 70% later in the season (70 days after planting) as the sorghum was heading in the dryland plots. Similar reductions in greenbug numbers were observed in the irrigated plots. However, because greenbug populations were below economic levels, yield differences between treated and untreated hybrids were not significantly different.

PROCEDURES
Treated and untreated seed of five sorghum hybrids (NC+ 271, Cargill 607E, DeKalb DK-56, Deltapine 1552, Pioneer 8500) were obtained from Gustafson, Inc. for use in the trial. Part of each seed lot had been treated with Gaucho™480 (imidacloprid) at a rate of 8 oz per 100 lb of seed (4 oz ai/cwt). Plots were established on 3 and 4 June at the Southwest Research-Extension Center, Finney County, Kansas. Plots were two rows (5 ft) by 22 ft, arranged in a randomized split plot design, and replicated four times. Seed was planted with a cone planter using 7 g of seed/row (12.2 lb seed/acre) in the irrigated trial and 1.5 g of seed/row (2.6 lb seed/acre) in the dryland trial. Ramrod and Atrazine were used for weed control.
Greenbugs were sampled in the dryland plots on 21 June (18 days after planting) by visually examining five plants in each row in each plot. Late-season greenbug counts were made on 12 and 13 August (70 days after planting) by cutting off two plants per plot (one plant at random from each row) at ground level and visually searching them for greenbugs. Yields were taken by machine harvesting the plots and calculating yields on a bu/acre basis.

RESULTS AND DISCUSSION
Low numbers of greenbugs were noticed in the plots a few days after planting, and counts made in the dryland plots indicated that the Gaucho was very effective at controlling this early-season invasion (about 99% control). Low numbers of greenbugs also were observed in mid-August, and counts showed about a 70% reduction in greenbug numbers in both the dryland and irrigated trials. Gaucho is a seed treatment, so the cost per acre is dependent on the amount of seed used to plant each acre. In these trials, the costs on a per acre basis were estimated to be about $2.80/acre on the dryland plots and $13.30/ acre on the irrigated plots. Thus the significant reduction in greenbug numbers and the low cost per acre makes this treatment fairly attractive to dryland sorghum producers. However, in this particular year, greenbug numbers were low. Although the Gaucho provided significant reductions in greenbug numbers even late in the season, yields were not significantly affected by the Gaucho treatment when averaged across hybrids. Thus, these trials indicate that Gaucho can be equally effective in reducing greenbug numbers in both dryland and irrigated plots, and even though the treatment is cheaper when using dryland seeding rates, the economics of the treatment will depend on the severity of the pest populations.

SUMMARY
The T-band applications of Fortress failed to give significant reductions of rootworm damage in this trial, probably because of the extremely dry conditions immediately after planting. However, the in-furrow applications did significantly reduce rootworm damage. No difference was observed between the conventional and the SmartBox™ applications of Fortress.

INTRODUCTION
This experiment was designed to test Fortress applied at planting with conventional or SmartBox™ application technology for the control of corn rootworm larvae.

PROCEDURES
Plots were planted at 30,600 seeds per acre on 9 May in a furrow-irrigated field at the Southwest Research-Extension Center, in Finney County, Kansas. The field was prewatered on 9 April, but the seed-bed dried out and the field was watered again 24 May to complete emergence. The soil type was a Richfield silt loam with a pH of 7.5 and an organic matter content of 1.5%. Plots were two rows (5 ft) by 50 ft long, arranged in a randomized complete block design, and replicated four times. Plots were separated by 10 ft alleyways at the end of each plot and four rows of border corn between each plot. Planting time treatments were applied as a 7-inch band over the open seed-furrow (T-band) or into the open seedfurrow (in-furrow) with either a standard John Deere™ planter-mounted insecticide applicator or with a SmartBox applicator. Spring incorporators were used after the press wheels. Rootworm damage was evaluated on four plants from each plot on 9 July using the 6-point Iowa scale. The weather was very dry after planting, averaging 0.4 inches of pan evaporation for the first 17 days. Then 1.8 inches of rain fell on 26 May, and 6.5 inches of rain was recorded between planting and evaluation of the roots. Yields were taken by mechanically harvesting each plot and measuring rows to correct for gaps created by the destructive sampling.

RESULTS AND DISCUSSION
Rootworm damage was severe, causing noticeable stunting, lodging, and stand loss. The in-furrow treatments of Fortress (both standard and SmartBox) gave significant control of rootworm damage, whereas the T-band applications did not. The T-band applications of Counter and Force also gave significant control of rootworm damage. Under the harsh conditions in this test, too much early volatilization of Fortress must have occurred to allow the banded treatments to be as effective as the standard treatments in reducing rootworm damage. The percent of plants with ratings greater than 3 were surprisingly high for all but the Counter treatment. All treatments except one (Fortress 5G, SmartBox, in-furrow) had significantly higher yields than the untreated check.

Southwest Research-Extension Center
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.

CORN BORER RESISTANCE AND GRAIN YIELD FOR BT AND NON-BT CORN HYBRIDS, 1996
by Larry Buschman, Phil Sloderbeck, Randy Higgins 1 , and Victor Martin 2 SUMMARY Six pairs of Bt-and non-Bt-corn hybrids were evaluated for corn borer resistance and grain yield performance. First generation ECB damage to whorl stage corn was reduced effectively by all six Bt corn hybrids. Second generation corn borer damage to posttassel corn was variable depending on the Bt event. Averaging over both locations ECB control averaged 96.3%, 97.5% and 26%; SWCB control averaged 100%, 85%, and 44%; and corn borer tunneling control averaged 99.7%, 91%, and 49%, for the three Bt events, Bt-11, MON810, and Bt 176, respectively. Total grain yields in the unsprayed blocks at St. John averaged 144.6 and 164.6 bu/acre in the non-Bt and Bt corn, respectively, for an advantage of 20 bu/acre for Bt corn. In non-Bt corn, the grain yield from fallen plants in the unsprayed blocks averaged 42.9 bu/acre. In Bt corn, the grain yield from fallen plants averaged 0, 4.9 and 27.5 bu/acre for the three Bt events, Bt-11, MON810, and Bt-176, respectively.

INTRODUCTION
The new corn borer-resistant Bt corn hybrids have shown outstanding resistance to the European corn borer (ECB), Ostrinia nubilalis (Hübner), and the Southwestern corn borer (SWCB), Diatraea grandiosella Dyar. Bt corn has been genetically engineered to express the delta endotoxins originally isolated from the bacterium, Bacillus thuringiensis. This is the same protein that is found in some Bt insecticide sprays. This protein is toxic to certain lepidopterous larvae, including the two corn borers, which are among the most important pests of corn in North America. Each insertion of genetic material into a new hose is referred to as an event. Once the event is created it can be transferred to different hybrids using standard breeding procedures. These trials were conducted to evaluate the corn borer resistance of different Bt corn hybrids and to evaluate grain yield performance under insecticide-protected and unprotected conditions.

PROCEDURES
At the Southwest Research-Extension Center near Garden City, KS, corn hybrid plots were machine planted on 16 May at 28,000 plants/acre. At the Sandyland Experiment Field near St. John, KS, corn hybrid plots were machine planted on 17 May at 26,000 plants/acre. The plots were four rows wide (10 ft.) and 30 ft long at Garden City and 22 ft long at St. John. Two additional rows of Bt corn were planted as border rows between the plots to reduce the impact of larval migration from untreated plots. The alleyways were 3 feet wide. The experimental design was a split-plot with four replications; however, at Garden City, two replications were abandoned for late-season observations and yield measurements because of uneven emergence and stand problems. The main plots were insecticide-protected versus insecticide unprotected, and the sub-plots were the 12 corn hybrids. The protected blocks were sprayed on 24 July at St. John and on 6 Aug. at Garden City with bifenthrin at 0.08 lb. AI/acre. The 12 hybrid entries included six pairs of corn hybrids (  generation ECB infestation was augmented manually by adding 40 to 50 ECB neonate larvae to the first 15 plants of one of the two center rows. Manual infestations were made on 8 and 9 July at Garden City when the plants were at the 14-leaf stage. At St. John, manual infestations were made on 12 and 13 July when the plants were at the 18-leaf stage. About 14 days after infestation, the plots were rated for first generation shot-hole damage, using the Guthrie 1 to 9 scale. Natural ECB and SWCB infestations accounted for the second generation infestation. Five consecutive plants in each of the two center rows from each plot were dissected to measure corn borer tunneling and record the numbers of each species of corn borer. Kernel damage (mostly corn earworm (CEW), Helicoverpa zea,(Boddie)) was recorded as percent of kernels damaged on each ear. Stalk rot rating was recorded as the number of internodes at the base affected by stalk rot. Yield was determined by hand harvesting the two middle rows of each plot in late Oct. Ears from standing plants and those from fallen plants (primarily from SWCB) were harvested separately. Yields per acre were calculated for fallen and total grain at 15.5% moisture.

Fig. 1. First generation ECB feeding damage in 12 corn hybrids including six pairs of Bt and non-Bt-corn hybrids planted at St. John and Garden City, 1996.
Natural first-generation infestation was absent. Feeding damage from the manually infested ECB was also light, up to 2.3 at St. John and up to 3.0 at Garden City on the 1 to 9 Guthrie scale. Al1 six Bt-corn hybrids had ratings for first generation ECB feeding damage that were significantly lower than those of the non-Bt counterparts. Second generation SWCB pressure was heavy at both locations and averaged up to 10.75 larvae in 10 plants. SWCB control averaged 100%, 85%, and 44% for the three Bt events, MON810, respectively. Control in the three "YieldGard" Bt hybrids (Bt-11 and MON810) averaged 95%, whereas control in the three Bt-176 hybrids averaged 44%. The insecticide treatment gave 95% control of SWCB at St. John and 72% control of SWCB at Garden City (data not shown).
38 Fig. 3. Number of second generation ECB larvae in 12 corn hybrids including six pairs of Bt and non-Bt-corn hybrids planted at St. John and Garden City, 1996.
Second generation ECB pressure was somewhat lower then the SWCB pressure and may have been suppressed somewhat through cannibalism by SWCB. The ECB pressure averaged up to 6.25 and 5.5 larvae per 10 plants at St. John and Garden City, respectively. ECB control averaged 96.3%, 97.5% and 26% for the three Bt events, MON810, respectively. Control in the three "YieldGard" Bt hybrids (Bt-11 and MON810) averaged 96.6%, whereas control in the three Bt-176 hybrids averaged 26%. The insecticide treatment gave 78% control of ECB at St. John and 38% control of ECB at Garden City (data not shown). Second generation corn borer tunneling damage to posttassel corn averaged up to 59.4 cm at St. John and up to 35.6 cm at Garden City. Corn borer tunneling was reduced by averages of 99.7%, 91%, and 49%, for the three Bt events, Bt-11, MON810, and Bt-176, respectively. Reduction in tunneling for the three "YieldGard" Bt hybrids (Bt-11 and MON810) averaged 96.8%, whereas reduction in tunneling for the three Bt-176 hybrids averaged 49%. The insecticide treatment reduced tunneling by 96% at St. John and 68% at Garden City (data not shown). Kernel damage was caused primarily by corn earworm, but some corn borer activity occurred as well. Reductions in kernel damage averaged 39.7%, 69.8%, and 22.0% for the three Bt events, Bt-11, MON810, and Bt-176, respectively. The insecticide treatment reduced kernal damage by 40% and 18% in the non-Bt hybrids and 12% and 29% in the Bt hybrids at St. John and Garden City, respectively (data not shown). Total grain yields in the unsprayed blocks at St. John averaged 144.6 and 164.6 bu/acre in the non-Bt and Bt corn, respectively, giving an advantage of 20 bu/acre for Bt corn. In the sprayed blocks, total grain yields averaged 167.5 and 163.2 bu/acre in the non-Bt and Bt corn, respectively, giving an advantage of 4.3 bu/acre for the non-Bt corn. In non-Bt corn, the grain yield from fallen plants in the unsprayed blocks averaged 42.9 bu/acre. In Bt corn, the grain yield from fallen plants averaged 0, 4.9, and 27.5 bu/acre for the three Bt events, Bt-11, MON810, and Bt-176, respectively. The standard hybrid, Pioneer 3162, yielded only 142.0 bu/acre, apparently because of gray leaf spot disease. Total harvested ears averaged 66 per plot or 25,000 per acre. Only the B73/Mo17 line had significantly fewer ears then the rest of the hybrids.

EVALUATION OF REGENT INSECTICIDE FOR EARLY-SEASON INSECT CONTROL IN CORN, 1996
by Larry Buschman and Phil Sloderbeck using the 6-point Iowa scale. Plant stunting also was rated visually as percent reduction in biomass relative to the best corn rootworm treatment (Counter). The banded treatment on 8-inch corn was made on 13 June with a hand sprayer. Whorl-stage applications were made on 11 July using a high clearance sprayer with three nozzles directed at each row and calibrated to deliver 20 gal/acre at 2 mph and 40 psi. A total of 6.5 inches of rain was recorded between planting and taking the root ratings and another 1.3 inches of rain was recorded between 9 July and 19 July when the corn borer ratings were taken. To assure first generation corn borer pressure, five European corn borer egg masses were pinned to every third plant in a 15-plant marked section in each plot on 25 June. These plants were evaluated for corn borer injury on 19 July using the Guthry scale and by dissecting plants to determine the number of corn borers and the amount of tunneling. Second generation damage was evaluated on 30 September by dissecting 15 plants in each plot. Yields were taken by mechanically harvesting each plot and measuring rows to correct for gaps created by the destructive sampling.

RESULTS AND DISCUSSION
Rootworm damage was severe, causing noticeable stunting, lodging, and stand loss. The in-furrow applications of Counter, Regent, and EXP 61216A applied at planting all significantly reduced the rootworm feeding injury. The banded application of Regent on 8-inch corn was applied too late to be very effective at reducing the rootworm damage. The planting-time applications of Regent and EXP 61216A reduced the amount of leaf injury from the manually applied first generation corn borer. The banded application of Regent on 8-inch corn significantly reduced damage by first generation corn borer. However, all of the Regent treatments reduced the amount of tunneling and the number of larvae from SUMMARY Regent was shown to reduce rootworm damage when applied in-furrow at planting and to reduce corn borer numbers and tunneling when applied at planting, banded on 8-inch corn, or broadcasted on whorl-stage corn. However, surprisingly, Regent also appeared to reduce second generation corn borer numbers and tunneling.

INTRODUCTION
This experiment was designed to test Regent applied at planting and at the whorl stage for the control of corn rootworm larvae and corn borer larvae. Regent is a new soil insecticide that is not yet registered for use in corn.

PROCEDURES
Plots were planted at 30,600 seeds per acre on 9 May in a furrow-irrigated field at the Southwest Research-Extension Center, in Finney County, Kansas. The field was prewatered on 9 April, but the seed-bed dried out, and the field was watered again on 24 May to complete emergence. The soil type was a Richfield silt loam with a pH of 7.5 and an organic matter content of 1.5%. Plots were 2 rows (5 ft) by 50 ft long, arranged in a randomized complete block design, and replicated four times. Plots were separated by 10 ft alleyways at the end of each plot and with four rows of border corn between plots. Planting-time granular treatments were applied as a 7-inch band over the open seed-furrow (T-band) or into the open seed-furrow (in-furrow) with planter-mounted John Deere™ granular applicators. The liquid applications at planting were made with a CO 2 backpack sprayer mounted on the planter with nozzles directed into each furrow delivering 1.5 gal/acre. Rootworm damage was evaluated on four plants from each plot on 9 July Southwest Research-Extension Center Means followed by same letter do not significantly differ (P=0.05, LSD)

*These treatments not yet registered for use on corn.
the first generation corn borers . Surprisingly, the infurrow planting-time application of Regent also significantly reduced numbers of second generation European corn borer and corn borer tunneling. Yield loss appeared to be associated with rootworm injury rather than corn borer injury.

WEED CONTROL IN NO-TILL DRYLAND GRAIN SORGHUM IN WESTERN KANSAS
by Curtis Thompson and Alan Schlegel SUMMARY Sorghum yields were highest when broadleaf and grass weeds were controlled with preemergence treatments. Atrazine was an essential component of all treatments that provided good broadleaf and grass control and the highest sorghum yields. The exception was Milopro, which is propazine and in the same chemical family as atrazine; it provided excellent weed control similar to atrazine. Lasso, Dual II, and Frontier alone did not provide adequate control of pigweed, kochia, or Russian thistle. Peak, Permit, Banvel, Buctril, or 2,4-D did not provide any grass control. Sorghum yields were low when either grass or broadleaf weeds were not controlled.

INTRODUCTION
The greatest factor limiting production of dryland sorghum in western Kansas is moisture. No-till increases the efficiency of moisture storage, which in return has increased grain production. Control of broadleaf and grass weeds is essential so that the benefits of this no-till system can be translated into increased grain production. Grass problems tend to increase in the no-till wheat-sorghum-fallow system. The following study evaluated pre-and postemergence herbicides for broadleaf and grass weed control in grain sorghum planted no-till into wheat stubble.

PROCEDURES
Pioneer 8771 Concep-treated seed was planted no-till into wheat stubble at 30,000 seeds/acre in 30inch rows, and preemergence treatments were applied on May 17 with a hand-boom CO 2 pressurized plot sprayer delivering 20 gpa. Landmaster at 40 oz/acre was broadcast over the entire experiment to control all emerged weeds on May 17. Postemergence treatments were applied as previously described to 2-to 6-inch broadleaf weeds, 4-to 5-leaf volunteer wheat, 1-to 3-inch witchgrass, and 5-collar sorghum approximately 6 to 7 inches tall on June 20. Climatic conditions, soil characteristics, and weed densities are presented in Table 1. Crop injury and weed control were evaluated visually on July 2, and heads were counted and weed control evaluated again on October 25 prior to grain harvest. Plots were 10 by 30 feet. Grain was harvested from two rows 27 feet long with a plot combine on October 28.

RESULTS AND DISCUSSION
Sorghum yields ranged from 30 to 111 bu/acre and were strongly correlated to the level of grass and broadleaf weed control (Table 2). All treatments containing atrazine provided grass suppression or control and broadleaf weed control, which lead to higher grain yields. Test weights tended to increase as yields increased, indicating that kernel fill was better when weed competition was less. The number of heads/acre correlated well with yields and weed control ratings.
Sorghum was injured by atrazine, and atrazinecontaining compounds, Guardsman, Bicep Lite II, and Bullet applied preemergence (Table 2). Frontier alone caused more injury to sorghum than Dual II or Lasso applied alone. Injury from preemergence treatments did not correlate well with grain yield, indicating that sorghum recovered from the injury and that weed control was a more critical factor affecting yield. Postemergence treatments that caused sorghum injury were 2,4-D and Shotgun (2,4-D + atrazine). Apparently, sorghum did not recover from the 0.5 lb rate of 2,4-D and yield was reduced compared to yields from sorghum treated with 0.375 lb of 2,4-D.
All treatments without atrazine failed to control either broadleaf or grass weeds (Table 3), resulting in poor sorghum yields. Atrazine was the essential Richfield silt loam component that provided broadleaf control with grass herbicides and grass control or grass suppression with broadleaf herbicides. Atrazine was the essential component and the only herbicide that provided adequate control of volunteer wheat. Preemergence treatments provided the most consistent weed control (Table 3) and highest sorghum yields. The exceptions were Frontier, Dual II, and Lasso applied alone. Volunteer wheat and broadleaf weeds escaped these treatments. Control of pigweed species with these herbicides ranged from 50 to 60% at the early evaluation, which was a bit disappointing. Insufficient moisture likely caused this poor control.

Southwest Research-Extension Center
Peak generally provided excellent control of pigweed species and acceptable control of kochia and Russian thistle. However, tankmixing with other compounds having broadleaf weed activity increased the control ratings for kochia and Russian thistle above 95% (Table 3). Permit did not control broadleaf weeds as well as Peak. Banvel, Buctril, Peak, Permit, or 2,4-D did not provide any grass control; thus, sorghum yields were suppressed by witchgrass and volunteer wheat competition.
Milopro and atrazine applied preemergence gave the best overall weed control for single herbicide treatments (Table 3). Preemergence atrazine becomes a very economical treatment for dryland sorghum. Under severe grass pressure, atrazine may not provide sufficient control.     Southwest Research-Extension Center SUMMARY Corn emerged before weeds, which greatly enhanced control of many treatments. Under these conditions, herbicides in the chloroacetamide class produced much higher levels of broadleaf weed control than are normal. Therefore, the broadleaf control data here should be used with caution. Under these much more competitive conditions, even the untreated plots produced yields ranging from 59 to 70 bu/acre. Excellent weed control more than doubled yield compared to the untreated control.

INTRODUCTION
This study was designed to compare 58 tank mixes of herbicides applied at different times for control of weeds in Poast-resistant corn.

PROCEDURES
Weeds were planted as described in Table 1, and Poast-resistanct corn was planted as described in Table  2. All weed not mentioned in Table 1 were natural infestations. Herbicides were applied as described in Table 3. Weed number per square foot was counted every 1 to 2 weeks. Ratings on 6/27 and 8/5 are presented as representative of mid-season and lateseason weed pressure. Yield was determined by combine harvest and adjusted to 15.5% moisture.

RESULTS AND DISCUSSION
At the mid-season rating, most treatments that provided complete control were those that had shown good results in the past (Table 4). However, the outstanding control seen in treatments 40, 42, 46, and 55 was very atypical for this area. This is attributed to good emergence of the corn and little rainfall for the first several weeks after planting.
At mid-season, kochia data were highly variable primarily because of generally low densities. One should not use these data to select a herbicide to control kochia. They were included for the reader's use if they confirm results seen in other replicated research or to draw inferences about the total mix of weed species present and their impact on yield. This is also true of grassy sandbur data. Even though the data presented here are variable, they might be useful as a guide to further investigations because so few data are available on control of grassy sandbur.
Seed bed preparation is the foundation of any good weed control program. If moisture is available at the depth where corn is planted and unavailable in the top 1 to 2 inches, this dry soil acts as a de facto mulch allowing the crop to shade the ground before weeds emerge. This certainly was the case in this study.
Because of these conditions, many of the tank mixes that normally produce good grass control and modest to poor broadleaf weed control provided excellent broadleaf weed control. Therefore, the broadleaf control provided by chloroacetamide herbicides in this study should be used with caution unless similar conditions can be predicted.

SUMMARY
Peak, a new herbicide for wheat, gave excellent control of wild sunflower, Russian thistle, and buffalobur. Control of kochia, common lambsquarters, and mustard species was enhanced when Peak was applied with Banvel, Buctril, Bronate, or 2,4-D. The addition of 2,4-D to Peak or Ally did not provide adequate control of kochia. Probably, ALS-resistant kochia was present at the Hodgeman County site.

INTRODUCTION
Peak is a new herbicide registered for broadleaf weed control in wheat. Wheat produced in a wheat fallow or a wheat-summer crop-fallow rotation frequently has problems from winter annual and spring-emerging broadleaf weeds. Winter annual grass problems generally are eliminated in a wheatsummer crop-fallow rotation. In years when wheat stands are thin, broadleaf weeds can create severe harvesting problems in addition to utilizing moisture and reducing wheat yields and possibly reducing moisture and yields of the subsequent crop in the rotation. Two studies were established in Hodgeman County to evaluate broadleaf weed control in thin wheat stands.

PROCEDURES
Two experiments with 'Ike' wheat were established north and northeast of Jetmore in Hodgeman County. Plots were 10 by 30 feet. All treatments were applied with a hand-boom CO 2 -pressurized plot sprayer delivering 20 gpa on April 26. Treatments were Southwest Research-Extension Center 1 Hodgeman County, Agricultural Agent, Jetmore. applied to 0.5-to 2-inch kochia and Russian thistle, cotyledon to 2-inch common lambsquarters and wild sunflower, cotyledon to 1-inch buffalobur, 1-to 5inch treacle mustard and flixweed, and jointing (2node) wheat. Climatic conditions, soil characteristics, and weed densities are presented in Table 1. Crop injury and weed control were evaluated visually on May 10 and again on June 7. Wheat was not harvested because of low yield potential.

RESULTS AND DISCUSSION
Banvel and Banvel tank mixed with Peak were the only treatments to cause injury to wheat (Table  2). Banvel should not be applied to wheat after the jointing stage begins because of increased risk of crop injury. The extremely dry winter had delayed the emergence of winter annual and spring annual broadleaf weeds; thus, treatments were applied later than normal to the wheat crop. No herbicide injury was observed at the DeWayne Craghead site (data not shown).
Peak alone or tank mixed with other broadleaf herbicides gave excellent control of wild sunflower, buffalobur, and Russian thistle (Table 2). Peak tank mixed with Banvel, Buctril, or Bronate gave better control of kochia and mustard species than Peak applied alone (Table 3). Peak tank mixed with 2,4-D and Ally tank mixed with 2,4-D gave excellent control of the mustard species, but did not give adequate control of kochia by the June 7 rating. Apparently, ALS-herbicide-resistant kochia was present in the study area, which allowed significant recovery of kochia (Table 3). Peak alone or 2,4-D alone gave less than 60% kochia control 6 weeks after treatment.

SUMMARY
Uncontrolled foxtail reduced yield from 36 to 49 bushels compared to treatments providing control. Although atrazine alone seldom improved grass control over that in the untreated plots, it did raise yield approximately 26 bu compared to the untreated control. Treatments providing good foxtail control raised yield 23 bu compared to atrazine alone.

INTRODUCTION
As the cheaper control compounds for broadleaf weeds have gained widespread use, a niche has opened for grassy weeds that are more expensive to control to gain supremacy. Atrazine, Banvel, Buctril, and 2,4-D have long been used for broadleaf control in southwest Kansas. They provide poor or inconsistent grass control; therefore, as expected, they have removed competition of the broadleaf weeds and allowed green foxtail to predominate in many fields. Therefore, the objectives of this test were to show yield losses caused by use of herbicide tank mixes designed to control only broadleaf weeds and to demonstrate the yield advantages associated with good green foxtail control.

PROCEDURES
Sorghum was planted as described in Table 1. Herbicide treatments were applied as described in Table 2 and 3.
Although low levels of broadleaf weeds were measured, they had no significant impact on yield. Therefore, only foxtail numbers per square foot and percent control calculated from these counts are presented. Grain was harvested with a plot combine, and all yields were adjusted to 15.5% moisture.

RESULTS AND DISCUSSION
Only one treatment reduced height at 8 days after post-emergence treatment, Peak following Dual II treatment (Table 4). As was seen in 1995 (See pages 46-50, 1996 Field Day Report), Peak injury was inconsistent. For example, height reduction seen with Dual and Peak treatment was not seen with treatments containing Peak alone or with Fe.
By 30 or 40 days after the first postemergence treatment, most herbicide treatments had reduced weed competition, so sorghum height increased (Table 5.) By July 16 and August 1, any treatment reducing foxtail numbers below 2.3 per square foot should be considered statistically equal. In mid August, any treatment reducing foxtail numbers below 2.7 per foot square should be considered statistically equal. Table  6 is provided to allow the reader to compare these data on the basis of a percent reduction in foxtail number calculated from the untreated control.
All treatments yielding below 23.7 bu were no better than the untreated plots ( Table 7). Most of these treatments, with the exception of treatments 9 and 10, are not labeled for grass control. The atrazine treatment that is not labeled for grass control provided poor grass control. However, it did provide elevated yield. It may have stunted foxtail enough to provide a yield increase. All treatments providing grass control

Southwest Research-Extension Center
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.   * Negative reduction is defined as an increase compared to untreated control.

IMPACT OF PALMER PIGWEED DENSITY ON CORN FORAGE QUALITY
SUMMARY Dry matter yield per acre decreased greatly as Palmer pigweed infestation in corn increased. Crude protein content in forage tended to increase and neutral detergent fiber value tended to decrease as pigweed infestation increased. However, the in-vitro digestibility decreased when pigweed was present. The overall effects of Palmer pigweed on total forage production and quality were negative.

INTRODUCTION
Feeding weeds to livestock is not a recommended practice, but it occurs occasionally because of unforeseen circumstances. Kochia works well when fed to nonlactating, gestating beef cows. It contains up to 16% crude protein, but because it has high levels of prussic acid, it must be managed appropriately. On occasion, infestation of cheat in wheat results in putting it up for hay. With corn, an early summer hail storm can destroy the crop and allow a pigweed infestation to occur. Whole-crop forage (corn + pigweed) occasionally is harvested. Therefore, in conjunction with an original study of the effect of Palmer pigweed on grain yield, we initiated an auxiliary study of its effect on forage yield and quality.

PROCEDURES
The corn hybrid Cargill 3700 was planted at 33,000 kernels/acre on May17, 1997 and Palmer pigweed seed was planted in clumps with a standard household salt shaker at 15, 30, 60, 120, and 240 clumps/10 ft. in a randomized complete block with 4 replications. Plot area was furrow irrigated with more than 12 inches of water within 24 hours after Southwest Research-Extension Center planting. Care was taken to maintain the level of water in the furrow below the position on the bed where pigweed seed was planted. Within 3 days, more than 1 inch of gentle rain fell. Pigweed emerged in 3 to 5days and was thinned to one plant per clump at the 3-to 5-leaf stage. These populations were maintained and all other weeds were removed throughout the season by twice weekly hand weeding. At late dent, a sample of 3.3 feet of row was harvested, and weed and crop masses were combined and analyzed for crude protein (CP), neutral detergent fiber (NDF), and in-vitro dry matter digestibility (IVDMD). From these samples, forage yields per acre also were calculated.

RESULTS AND DISCUSSION
A large reduction in dry matter (DM) yield per acre occurred as the level of pigweed infestation increased (P<.01) (Table 1). At 15 pigweed/10 ft of row, a 14% reduction occurred in DM yield, and with greater infestation, yield declined by 30 to 57%. This reduction in yield was greater than expected, given the visual evaluation of the amount of total plant material present.
The P-values of overall treatment effects for CP and NDF only tended to approach significance (P=.16). Numerically, values increased from 9.6% CP for samples with no pigweed infestation to averages of 10.6 to 12.3% CP if pigweed was present. Overall, the NDF value declined with increased pigweed infestation, but this trend was not significant (P=.16).
With an increased CP and decreased NDF (with greater pigweed infestation), one would have expected in-vitro digestibility to increase as well. However, the opposite occurred. In-vitro digestibility decreased numerically (P=.47) from 50% with no pigweed infestation to approximately 47% if pigweeds were present. Because the increased CP content and decreased fiber content were offset by lower digestibility, feed value was not increased with greater pigweed infestation. Also, with a 30 to 60% DM yield reduction, increased pigweed infestation apparently is detrimental not only to grain production but to total forage production as well.

Southwest Research-Extension Center
Corn was evaluated for grain yield loss caused by simulated hail defoliation at two stages (8-leaf and 12-leaf). This was done in combination with two crop row spacings (15 in. and 30 in.). Additionally, two hybrids were used; 'Asgrow RX707,' a 109 day maturity hybrid, and 'Pioneer 3162,' a 114 day maturity hybrid.
Corn was planted on 4/25/96 with a White Air Seeder at 33,000 seeds/acre. Resulting stands at 30,000 plants per acre were kept weed free with Prowl/Bladex herbicide. Defoliation at 50% of the leaf area on selected plots was accomplished on 6/4/ 96 for the 8-leaf (8L) stage treatments and on 6/18/96 for 12-leaf (12L) stage treatments.
The two center rows of four row plots including four replications were hand harvested on 10/14/96.
Resulting grain yields as bushels per acre are shown in Table 1.
Data indicate about a 4% reduction in grain yield at the 8L stage from 50% defoliation when averaged over both hybrids and both row spacings. An approximate 10% grain yield reduction was indicated for the 12L stage with 50% defoliation when averaged over both hybrids and both row spacings. Yields were about 4% more with the 15-in. row spacing compared to the 30-in. row spacing, when averaged over both hybrids and all treatments.
The results suggest that narrow rows for corn did not affect the amount of loss caused by early-season defoliation. However, the narrow row spacing was beneficial to corn yields, regardless of whether or not defoliation occurred.