Southwest Research-Extension Center, Field Day 2012

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Phosphorus Fertilization of Irrigated Grain Sorghum
This publication from the Kansas State University Agricultural Experiment Station and Cooperative Extension Service has been archived.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.   Benefits of Long-Term No-till in a Wheat-Sorghum-Fallow Rotation 1

A. Schlegel, L. Stone 2 , and T. Dumler
Summary Grain yields of wheat and grain sorghum increased with decreased tillage intensity in a wheat-sorghum-fallow (WSF) rotation. Averaged over the past 11 years, no-till (NT) wheat yields were 6 bu/a greater than reduced tillage and 9 bu/a greater than conventional tillage. Grain sorghum yields in 2011 were 35 bu/a greater with long-term NT than short-term NT. Averaged across the past 11 years, sorghum yields with long-term NT have been twice as great as short-term NT (62 vs. 31 bu/a).

Procedures
Research on different tillage intensities in a WSF rotation at the Tribune Unit of the Southwest Research-Extension Center was initiated in 1991. The three tillage intensities in this study are conventional (CT), reduced (RT), and no-till (NT). The CT system was tilled as needed to control weed growth during the fallow period. On average, this resulted in four to five tillage operations per year, usually with a blade plow or field cultivator. The RT system originally used a combination of herbicides (one to two spray operations) and tillage (two to three tillage operations) to control weed growth during the fallow period; however, in 2001, the RT system was changed to using NT from wheat harvest through sorghum planting (short-term NT) and CT from sorghum harvest through wheat planting. The NT system exclusively used herbicides to control weed growth during the fallow period. All tillage systems used herbicides for in-crop weed control.

Results and Discussion
Since 2001, wheat yields have been severely depressed in 6 of 11 years, primarily because of lack of precipitation. Reduced tillage and no-till increased wheat yields (Table 1). On average, wheat yields were 9 bu/a higher for NT (25 bu/a) than CT (16 bu/a). Wheat yields for RT were 3 bu/a greater than CT even though both systems had tillage prior to wheat. NT yields were less than CT or RT in only 1 of the 11 years.
The yield benefit from RT was greater for grain sorghum than wheat. Grain sorghum yields for RT averaged 13 bu/a more than CT, whereas NT averaged 31 bu/a more than RT (Table 2). For sorghum, both RT and NT used herbicides for weed control during fallow, so the difference in yield could be attributed to short-term compared with long-term no-till. In 2011, sorghum yields were 35 bu/a greater with long-term NT than short-term NT. This consistent yield benefit with long-term vs. short-term NT has been observed since the RT system was changed in 2001. Averaged across the past 11 years, sorghum yields with long-term NT have been twice as great as short-term NT (62 vs. 31 bu/a). Tillage × year -------------bu/a ------------- Tillage × year -------------bu/a -------------

Introduction
Growing annual forages or cover crops in place of fallow in a wheat-fallow system is a farming practice that may potentially conserve and improve soil resources. Cover crops may particularly help to reduce wind and water erosion in semiarid regions such as the central Great Plains. Winter wheat-fallow rotation is a dominant cropping system in the region. This rotation is, however, highly vulnerable to wind erosion and soil quality degradation during the fallow phase due to reduced residue cover.
Although wind erosion is often a greater concern than water erosion in semiarid regions, water erosion from crop-fallow systems also can be significant. The limited precipitation in the semiarid Great Plains often occurs in the form of intense and localized rainstorms, which can cause large seasonal losses of soil and nutrients in runoff.
Cover crops are attracting attention, but the extent to which cover crops reduce water and wind erosion in semiarid regions is not well understood. Some producers want to grow annual forages in place of fallow rather than a cover crop; however, harvesting forages reduces the amount of residue left on the soil surface and might reduce soil erosion and improve soil quality less than cover crops. Thus, the effects of annual forages and cover crops on soil erosion need to be determined. This study assessed the effects of both annual forages and cover crops on wind and water erosion for a no-till, wheat-fallow rotation.

Procedures
We studied wheat-fallow rotation managed with a number of cover crops and annual forages under no-till for five years at the Southwest Research-Extension Center. Within the fallow phase, treatment plots consisted of chemical fallow, winter crops (hairy vetch, winter lentil, Austrian winter pea, winter triticale, and each winter legume combined with winter triticale), spring crops (spring lentil, spring field pea, spring triticale, and each spring legume combined with spring triticale), winter and spring peas grown for grain, and continuous winter wheat. Each plot was split in two, with half the plot managed under cover crops (non-hayed) and the other half under annual forage (hayed.) The treatments were replicated three times in a randomized complete block design.
For the study of wind erosion, seven treatments, including fallow (control), winter lentil, spring pea, spring lentil, winter triticale, spring triticale, and continuous winter wheat, were selected from the larger experiment. To study the effects of cover crop haying on wind erosion, winter triticale and spring triticale with half the plot managed under cover crops (non-hayed) and the other half under annual forage (hayed) were selected. For the study of water erosion, five cover crop treatments including fallow (control), winter lentil, spring triticale, spring pea, and winter triticale were selected.
Two soil parameters that directly influence the soil's susceptibility to wind erosion, wind-erodible fraction of the soil and aggregate size expressed as geometric mean diameter of dry aggregates, were used to evaluate wind erosion. About 5 lb of soil sample were collected from the 0-to 2-in. depth from the 10 treatments in August 2011.

Wind erosion
Replacing fallow with cover crops affected all soil erodibility properties. Cover crops generally reduced the wind-erodible fraction of the soil and increased the size of aggregates compared with fallow. For example, spring lentil reduced the erodible fraction by 73% ( Figure 1A) and increased geometric mean diameter of dry aggregates by 65% compared with fallow ( Figure 1B). These results indicate that replacing fallow with a crop increased soil macroaggregation. The larger the aggregates, the lower the aggregate breakdown and the lower the soil's susceptibility to wind erosion. Results also suggest that the effects of cover crops on reducing wind erosion depend on cover crop species.
Effects of harvesting an annual forage compared with growing a cover crop on wind erosion were not significant ( Figures 1A and 1B). Although haying of winter and spring triticale increased the wind-erodible fraction and reduced aggregate size relative to winter and spring triticale without haying, differences were not statistically significant due to the high variability in data. Based on the trend for increased wind erosion with haying, we suggest that haying of cover crops may significantly increase wind erosion crops in the long term.
Continuous wheat also reduced erodible fraction ( Figure 1A) and increased geometric diameter of aggregates ( Figure 1B) relative to fallow. Annual straw input and perma-nent straw cover may be the reasons for the greater ability of continuous wheat to reduce wind erosion.

Water erosion
The five selected cover crop treatments also affected water erosion. Cover crops reduced water erosion, but the effects were significant only at the 0.10 statistical probability level. This result suggests that cover crops may have more beneficial effects on reducing wind erosion than water erosion in this soil with moderate slopes (<3%). Cover crops generally reduced runoff (Figure 2A), sediment loss ( Figure 2B), and loss of sedimentassociated total P and nitrates (NO 3 -N). Winter triticale, spring pea, and spring triticale had large effects and reduced runoff by 350% relative to fallow ( Figure 2A). Winter triticale and spring pea reduced sediment loss by 370%, but winter lentil and spring triticale had no effects ( Figure 2B). Winter triticale and spring pea reduced losses of total P and NO 3 -N by 380% compared with fallow.
Results show that 60% of simulated rain was lost as runoff from plots without cover crops, and only about 13% was lost from plots with winter triticale, spring pea, and spring triticale cover crops. Winter triticale and spring pea cover crops reduced sediment loss by about 0.53 tons/a under a single and simulated rainfall event at 3 in./hour. Winter triticale appeared to be the most effective cover crop treatment for reducing runoff and loss of sediment and nutrients.

Conclusions
Results from this study showed that cover crops reduced wind and water erosion in a no-till, wheat-fallow rotation in this semiarid region. In general, the wind-erodible fraction of the soil was lower and soil aggregates were larger when cover crops were included in the wheat-fallow rotation. Similarly, runoff and sediment loss were reduced with the inclusion of cover crops. Winter triticale and spring pea cover crops were particularly effective for reducing runoff and sediment loss. Our study also showed that continuous wheat was effective to reduce wind erosion risks compared with fallow. Haying of winter and spring triticale appears not to have significant effects on wind erosion in the short term. Long-term (>5 years) monitoring is needed to determine conclusively the effects of cover crop haying on wind erosion and other soil and environmental parameters.
The use of cover crops in semiarid regions has been questioned because cover crops use water and may thus reduce plant-available water for the subsequent crops. Our results suggest that cover crops may contribute to water storage by reducing runoff, which may somewhat reduce the negative effects of cover crops on soil water storage for the subsequent crops. Selection of the most suitable or drought-tolerant species and development of improved management strategies (i.e., early termination) may reduce the adverse effects of cover crops on water storage.   Figure 2. Impact of cover crops on runoff and sediment loss. Means or bars with the same lowercase letter are not statistically different at P = 0.10.

Introduction
Interest in growing cover crops and replacing fallow with a cash crop has necessitated research on species that are adapted to southwest Kansas and their forage biomass potential. Fallow stores moisture, which helps stabilize crop yields and reduce the risk of crop failure; however, only 25 to 30% of the precipitation received during the fallow period of a no-till wheat-fallow rotation is stored. The remaining 70 to 85% precipitation is lost primarily to evaporation. Moisture storage in fallow is more efficient earlier in the fallow period when the soil is dry and during the winter months when the evaporation rate is lower. Increasing cropping intensity without reducing winter wheat yield may be possible. Growing a cover crop that produces a lot of biomass may reduce evaporation; in contrast, evaporation may be greater following a cover crop harvested for forage. This study evaluated the forage biomass yield of several winter and spring crops.

Procedures
Fallow replacement crops (cover, annual forage, or short-season grain crops) have been grown during the fallow period of a no-till wheat-fallow cropping system every year since 2007. Crops were either grown as cover, harvested for forage (annual forage crop), or harvested for grain. Both winter and spring crop species were evaluated. Winter species included yellow sweet clover (Melilotus officinalis (L.) Lam.), hairy vetch (Vicia villosa Roth ssp.), lentil (Lens culinaris Medik.), Austrian winter forage pea (Pisum sativum L. ssp.), Austrian winter grain pea (Pisum sativum L. ssp.), and triticale (×Triticosecale Wittm.). Spring species included lentil (Lens culinaris Medik.), forage pea (Pisum sativum L. ssp.), grain pea (Pisum sativum L. ssp.), and triticale (×Triticosecale Wittm.). Crops were grown in monoculture and in two-species mixtures of each legume plus triticale. Crops grown for grain were grown in monoculture only. Winter lentil was grown in place of yellow sweet clover beginning in 2009. Crops grown in place of fallow were compared with a wheat-fallow and continuous wheat rotation for a total of 16 treatments (Table 1). The study design was a split-split-plot randomized complete block design with 4 replications; crop phase (wheat-fallow) was the main plot, fallow replacement was the split-plot, and fallow replacement method (forage, grain, or cover) was the split-split-plot. The main plot was 480 ft wide and 120 ft long, the split plot was 30 ft wide and 120 ft long, and the split-split plot was 15 ft wide and 120 ft long.
Winter crops were planted approximately October 1. Winter cover and forage crops were chemically terminated or forage harvested approximately May 15. Spring crops were planted between the end of February and middle of March. Spring cover and forage crops were chemically terminated or forage harvested approximately June 1. Forage biomass yield for both cover crop and forage crop was determined from a 3-ft by 120-ft area cut 3 in. high using a small-plot Carter forage harvester from within the split-split-plot managed for forage. Winter and spring grain peas and winter wheat were harvested with a small plot combine from a 6.5-ft by 120-ft area at grain maturity, which occured approximately the first week of July.
Volumetric soil moisture content was measured at cover crop termination and winter wheat planting using a Giddings Soil Probe (Giddings Machine Company, Windsor, CO) to a 6-ft soil depth. Grain yield was adjusted to 13.5% moisture content and test weight was measured using a grain analysis computer. Grain samples were analyzed for nitrogen content. Forage samples were weighed wet, then a homogenized subsample was collected, dried at 50ºC in a forced-air oven for 96 h, weighed dry for dry matter yield, and sent to a commercial laboratory for crude protein (CP), acid detergent fiber (ADF), and neutral detergent fiber (NDF) determination.

Results and Discussion
Forage yield of crop species varied by year due to differences in winter survival and moisture conditions. Winter species (2,336 lb/a) tended to yield more than spring species (1,493 lb/a), although there were differences between years (P = 0.003) ( Figure  1). Forage yield data from 2007 was not included in the analysis since previous land area management might have caused variation in yield. Forage yield data from 2008 through 2011 were analyzed. Yellow sweet clover did not produce any harvestable biomass in 2007 or 2008 and was replaced with winter lentil beginning in 2009.
In 2008, yields of winter (2,712 lb/a) and spring crops (2,030 lb/a) did not differ (P = 0.08), and all winter crops survived the winter ( Figure 2). Winter pea showed some visual sign of winter injury, but all other winter crops survived the winter without injury symptoms. Treatments that included winter triticale yielded the most, and treatments with spring triticale yielded the second most. Spring pea, hairy vetch, winter pea, and spring lentil yielded the least. Yellow sweet clover did not produce any harvestable biomass (data not shown).
In 2009, winter crops (2,708 lb/a) yielded more than spring crops (1,296 lb/a) ( Figure  3). Winter stand loss was estimated at 50% for winter pea and 95% for hairy vetch. Winter lentil showed no signs of winter injury. Winter survival of winter pea and hairy vetch was greater when grown in mixture with winter triticale than in monoculture. Treatments with winter triticale yielded the most. Winter pea/triticale (5,220 lb/a) yielded more than hairy vetch/triticale (4,503 lb/a) or winter lentil/triticale (3,703 lb/a), which was likely due to the winter peas adding to the yield of triticale grown alone (4,726 lb/a). Treatments with spring triticale yielded the second most, ranging from 1,266 to 1,815 lb/a, which did not differ from spring peas grown alone (1,467 lb/a). Winter pea, spring lentil, and winter lentil yielded the least. Hairy vetch did not yield any harvestable biomass due to winter-kill.
In 2010, winter crops (3,018 lb/a) yielded more than spring crops (1,548 lb/a) ( Figure  4). Winter stand loss was estimated at 60% for winter pea and 70% for hairy vetch. Winter lentil showed no signs of winter injury. Winter survival of winter pea and hairy vetch was greater when grown in mixture with winter triticale than in monoculture. Treatments with winter triticale yielded the most, and there were no differences between that set of treatments. Winter triticale treatments yielded between 4,589 and 5,174 lb/a. Treatments with spring triticale yielded the second most, ranging from 1,689 to 2,435 lb/a. Spring triticale (1,772 lb/a) did not yield any more than spring pea (1,398 lb/a). Winter pea, hairy vetch, winter lentil, and spring lentil yielded the least. 2011 was an abnormal year. The fall of 2011 was extremely dry, and winter treatments had to be reseeded due to very dry soil conditions at planting. Only 6.77 in. of precipitation occurred between October 1, 2010, and July 1, 2011. Of this, only 2.15 in. of precipitation occurred between October 1, 2010, and April 1, 2011. The dry conditions and lack of fall and winter precipitation favored spring crops more than winter crops. Spring crops (968 lb/a) yielded more than winter crops (501 lb/a; Figure 5). The combination of dry soil conditions and winter-kill resulted in no harvestable yield of winter lentil, hairy vetch, and winter pea. Winter survival of winter pea and hairy vetch was greater grown in mixture with winter triticale than in monoculture. Spring triticale (1,407 lb/a), spring pea (1,264 lb/a), spring lentil/triticale (1,091 lb/a), and hairy vetch/triticale (1,011 lb/a) yielded the most. Spring lentil yielded the least amount of harvestable yield (174 lb/a). Spring pea/triticale, winter lentil/triticale, winter triticale, and winter pea/triticale yielded less than spring triticale.
Averaged over years from 2008 through 2011 (2007 excluded because it was the initial year of the study), winter triticale treatments yielded the most and spring triticale treatments yielded the second most. Spring triticale yields were similar to spring pea/ triticale and spring pea, but spring pea/triticale yielded more than spring pea, indicating the addition of spring pea to spring triticale tended to increase yield. Winter pea, spring lentil, hairy vetch, and winter lentil yielded the least. Winter triticale averaged 3,675 lb/a, and spring triticale averaged 1,869 lb/a.

Conclusions
Forage yield varied based on growing season conditions, primarily precipitation and winter injury. Winter peas and hairy vetch had significant winter injury and stand loss. Winter lentil survived the winter well but had low yield potential and did not add to the yield potential of winter triticale. Winter legumes had less winter injury when grown in combination with triticale, and occasionally winter pea or hairy vetch increased the yield potential of winter triticale; however, the additional seed cost and risk of winter injury make planting winter pea or hairy vetch with winter triticale unadvisable. Winter triticale survived the winter well every year and yielded the most except in 2011, which had a very dry fall and winter.
Spring triticale treatments and spring peas yielded the second most. Spring peas grown in combination with spring triticale tended to increase the yield of spring triticale, whereas spring lentil grown in combination with spring triticale did not improve yield. Spring triticale averaged slightly more yield (439 lb/a) than spring pea. Spring and winter lentil did not produce enough biomass for forage but may be grown as a cover crop where biomass production is not a primary concern. H a i r y v e t c h / t r i t i c a l e W i n t e r a v e r a g e W i n t e r l e n t i l H a i r y v e t c h S p r i n g l e n t i l W i n t e r p e a S p r i n g p e a S p r i n g l e n t i l / t r i t i c a l e S p r i n g t r i t i c a l e S p r i n g p e a / t r i t i c a l e W i n t e r l e n t i l / t r i t i c a l e  Cover crop W i n t e r p e a / t r i t i c a l e 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0 Biomass dry matter yield, lb/a H a i r y v e t c h / t r i t i c a l e W i n t e r a v e r a g e H a i r y v e t c h S p r i n g l e n t i l W i n t e r p e a S p r i n g p e a S p r i n g l e n t i l / t r i t i c a l e S p r i n g t r i t i c a l e S p r i n g p e a / t r i t i c a l e 1,000 0 Biomass dry matter yield, lb/a H a i r y v e t c h / t r i t i c a l e W i n t e r a v e r a g e W i n t e r l e n t i l H a i r y v e t c h S p r i n g l e n t i l W i n t e r p e a S p r i n g p e a S p r i n g l e n t i l / t r i t i c a l e S p r i n g t r i t i c a l e S p r i n g p e a / t r i t i c a l e W i n t e r l e n t i l / t r i t i c a l e W i n t e r t r i t i c a l e S p r i n g a v e r a g e 1,000 0 Biomass dry matter yield, lb/a H a i r y v e t c h / t r i t i c a l e W i n t e r a v e r a g e W i n t e r l e n t i l H a i r y v e t c h S p r i n g l e n t i l W i n t e r p e a S p r i n g p e a S p r i n g l e n t i l / t r i t i c a l e S p r i n g t r i t i c a l e S p r i n g p e a / t r i t i c a l e W i n t e r l e n t i l / t r i t i c a l e W i n t e r t r i t i c a l e S p r i n g a v e r a g e

Biomass dry matter yield, lb/a
H a i r y v e t c h / t r i t i c a l e W i n t e r a v e r a g e W i n t e r l e n t i l H a i r y v e t c h S p r i n g l e n t i l W i n t e r p e a S p r i n g p e a S p r i n g l e n t i l / t r i t i c a l e S p r i n g t r i t i c a l e S p r i n g p e a / t r i t i c a l e W i n t e r l e n t i l / t r i t i c a l e W i n t e r t r i t i c a l e S p r i n g a v e r a g e

Summary
Hail damage is a common occurrence throughout Kansas. This study evaluated the impact of simulated hail damage (stand thinning) on corn at at V5, V8, V11, and V14 growth stages in 2008, 2009, and 2010. The amount that the stand was thinned had a greater impact on corn yield components, yield, and grain quality than the crop stage at thinning. Plants thinned early tended to yield slightly more than plants thinned later. In part, this was because they were able to produce more kernels per ear than plants thinned at V14. Crop yield was reduced at each additional level of thinning. Corn yield was able to partly compensate for thinning by increasing kernel weight, kernels per ear, and ears per plant. Thinning reduced test weight and increased protein content.

Introduction
Hailstorms are a common cause of crop damage in Kansas. Diagnosing and determining the amount of crop injury is important in determining yield loss.
Hail damage always makes corn look bad, and can make for some sleepless nights.
Although the physical damage is apparent, the actual effect on yield is not as obvious. Potential corn yield losses from hail gradually increase as the crop matures, up to the silk stage, when peak yield loss occurs. After silking, yield losses from hail damage normally decline again.

From emergence through stem elongation (VE to V5)
Through the five-leaf stage of growth, the growing point of corn is below the soil surface. Hail damage could remove all five leaves but not damage the growing point.
A corn plant has 24 to 26 leaves at tasseling; even if the plant loses five of those leaves early on, it will still have the potential to have 19 to 21 leaves at tasseling. Yield will be reduced, but by much less than one might expect from the appearance of the plant.

From stem elongation to tassel (V6 to VT)
The growing point begins extending aboveground by the 6-leaf stage, although it is still protected by several layers of leaves and sheaths. The number of rows that will be in the ear is established by the 12-leaf stage. Stress during V8 to V11 can reduce row number. The number of kernels per row is not determined until about V17, just before tasseling. Hail damage and loss of leaf area during these stages of growth can increase the potential for yield loss. Hail can also cause stalk bruising during these stages of growth, but determining the amount of damage from stalk bruising is difficult until later in the season.

From tassel to maturity (VT to R6)
At VT to R1 (tassel to silk), the corn plant is more vulnerable to hail damage than at any other stage because the tassel and all leaves are exposed. No more leaves will be developed, and the plant cannot replace a damaged tassel. Furthermore, the stalk is exposed, with only one layer of leaf sheath protecting it. Unlike wheat, corn cannot fill from the stem if leaves are lost at this stage of growth. The six to eight leaves above the ear are the most important, and provide most of the grain fill.
The four-week period surrounding silking is critical to corn, and not only in regard to hail damage. Drought stress, excessive moisture, extreme heat, diseases, and high winds can all stress the plant and reduce yields at this stage of growth. Early in this period, stress can reduce kernel number by limiting potential ear size. Stress right at silking can reduce the number of kernels fertilized, and stress just after silking can cause fertilized kernels to abort.

Procedures
Corn was planted at 36,000 plants/a and thinned to 34,000 plants/a after all corn emerged. Corn was fully irrigated using an overhead pivot. Corn stands were thinned randomly by hand-thinning 0%, 25%, 50%, and 75% at V5, V8, V11, and V14, respectively. Plots were 4 rows wide on 30-in. centers and 30 ft long. Final plant stand, ears per plant, kernels per ear, yield, test weight, 1,000 kernel weight, and protein content were measured from the center 2 rows the full length of the plot. Plots were harvested with a plot combine at grain maturity. Grain yield was adjusted to 15.5% moisture content and test weight was measured using a grain analysis computer. Grain samples were analyzed for nitrogen and converted to protein content. This study was conducted in 2008, 2009, and 2011. For the purposes of this report, results from all years were shown.

Ears per plant
The number of ears produced per plant was not affected by year or crop stage. Stands thinned 75% had more ears per plant (1.11 ears/plant) than the other thinning levels (0.99 ears/plant) (P ≤ 0.01) ( Figure 4).

Conclusions
The amount that the stand was thinned had a greater impact on corn yield components, yield, and grain quality than the crop stage at thinning. Although not significant, plants thinned early tended to yield more than plants thinned later. In part, this was because plants thinned early were able to produce more kernels per ear than plants thinned at V14. Crop yield was reduced at each additional level of thinning, but corn yield was able to partly compensate for thinning by increasing kernel weight, kernels per ear, and ears per plant. Thinning reduced test weight and increased protein content.
This study found slightly different results than research conducted by Dr. Barney Gordon at the North Central Kansas Experiment Field. In that study, yield was affected more by the crop stage thinning that occurred, and thinning affected seed weight; in this study, thinning increased seed weight. In both studies, percentage yield loss was less than the percentage of the stand thinned at every growth stage.
When considering replanting due to poor stands or early season hail damage, keep in mind that planting corn in early June, in much of Kansas, can result in yield losses of up to 50% compared to a typical planting date. Based on the above data, retaining an existing stand even with as much as 50% stand loss would probably be better than replanting in early June. Much depends, of course, on the uniformity of the remaining stand and the weather for the rest of the growing season.

Introduction
Interest in growing cover crops and replacing fallow with a cash crop has necessitated research on wheat yields following a shortened fallow period. Fallow stores moisture, which helps stabilize crop yields and reduce the risk of crop failure; however, only 25 to 30% of the precipitation received during the fallow period of a no-till, wheat-fallow rotation is stored. The remaining 70 to 85% precipitation is lost primarily to evaporation. Moisture storage in fallow is more efficient earlier in the fallow period when the soil is dry and during the winter months when the evaporation rate is lower. Increasing cropping intensity without reducing winter wheat yield may be possible. This study evaluated the effects of replacing part of the fallow period with a cover, annual forage, or short-season grain crop on the following winter wheat yield.

Procedures
Fallow replacement crops (cover, annual forage, or short-season grain crops) have been grown during the fallow period of a no-till, wheat- Crops were grown in monoculture and in two-species mixtures of each legume plus triticale. Crops grown for grain were grown only in monoculture. Winter lentil was grown in place of yellow sweet clover beginning in 2009. Crops grown in place of fallow were compared with a wheat-fallow and continuous wheat rotation for a total of 16 treatments (Table 1.) The study design was a split-split-plot randomized complete block design with 4 replications; crop phase was the main plot, crop species was the split-plot, and termination method (forage, grain, or cover) was the split-split-plot.
Winter crops were planted approximately October 1. Winter cover and forage crops were terminated or harvested approximately May 15. Spring crops were planted from the end of February through the middle of March. Spring cover and forage crops were terminated or harvested approximately June 1. Winter and spring grain peas were harvested with a small plot combine at grain maturity, which was approximately July 1.
Volumetric soil moisture content was measured at cover crop termination and winter wheat planting using a Giddings Soil Probe (Giddings Machine Company, Windsor, CO) to a 6-ft soil depth. Grain yield was adjusted to 13.5% moisture content, and test weight was measured using a grain analysis computer. Grain samples were analyzed for nitrogen content.

Results and Discussion
Winter wheat yield In 2008, hail damaged the wheat crop 1 week before harvest; therefore, no statistical separation was made between treatments. Winter wheat yield following a fallow crop ranged from 21 to 26 bu/a, wheat yield following wheat was 13 bu/a, and wheat yield following fallow was 22 bu/a ( Figure 1).
In 2009, grain pea and winter clover/triticale yielded 7 and 9 bu/a less than fallow (83 bu/a), and spring pea yielded 7 bu/a more than fallow ( Figure 2). Continuous wheat yielded least of all (57 bu/a). All other treatments yielded similar to fallow.
In 2010, winter pea/triticale and winter triticale yielded 5 and 7 bu/a less than fallow (70 bu/a), and spring lentil/triticale and spring pea/triticale yielded 4 and 6 bu/a less than fallow (Figure 3). Continuous wheat yielded least of all (43 bu/a). All other treatments had yields similar to fallow. Wheat following cover crops yielded an average of 2.9 bu/a more than wheat following a hay crop.
In 2011, only 6.77 in. of precipitation occurred between October 1, 2010, and July 1, 2011. This drought resulted in low wheat yields and a greater impact of the preceding crop on wheat yield. Wheat grown following a winter cover or forage crop yielded less than fallow with the exception of winter lentil (22 bu/a), which yielded similar to fallow (23 bu/a) (Figure 4). Wheat yield following all other winter crops was reduced by 4 to 10 bu/a. Wheat yield following spring cover or forage crops was not affected as much as winter crops. Wheat yield following spring lentil, triticale, and lentil/triticale was similar to fallow and wheat following spring pea and pea/triticale was reduced 7 and 3 bu/a, respectively. Wheat following grain pea was reduced 11 bu/a, and wheat following wheat was reduced 16 bu/a compared with fallow.
Wheat harvested in 2012 will be the final wheat yield collected from a wheat-fallow rotation. Future research will evaluate replacing fallow in a wheat-grain sorghum-fallow rotation.
Averaged over years from 2009 through 2011 (2008 excluded due to hail damage), there was no difference whether the previous crop was grown as forage or cover (P = 0.09). Winter crops with triticale yielded 4 to 7 bu/a less than fallow, winter legume monocultures yielded similar to fallow, and all spring crops yielded similar to fallow ( Figure 5). Grain peas yielded 7 bu/a less, and continuous wheat yielded 23 bu/a less than fallow.

Cover vs. annual forage
Across years (2009)(2010)(2011), whether the previous crop was left as cover or harvested for forage did not affect wheat yield. In 2010, wheat following cover crops yielded an average of 2.9 bu/a more than wheat following a hay crop. This result indicates that the previous crop can be harvested for forage without negatively affecting wheat yield compared with growing a cover crop.

Conclusions
This study found the cropping system can be intensified by replacing part of the fallow period with annual forages or cover crops without reducing the following wheat yield. Winter triticale, continuous wheat, and grain peas reduced wheat yield, but all other treatments yielded similar to fallow. The reduced wheat yield following these treatments was likely due to less available soil moisture at wheat planting. Cover crops did not improve wheat yield. Forages provide an economic return, but cover crops are an expense to grow. A detailed economic analysis is needed; preliminary analysis suggests annual forages and grain peas increase returns whereas continuous winter wheat and cover crops reduce returns.

Summary
Research on four-year crop rotations with wheat and grain sorghum was initiated at the Southwest Research-Extension Center near Tribune, KS, in 1996. Rotations were wheat-wheat-sorghum-fallow (WWSF), wheat-sorghum-sorghum-fallow (WSSF), and continuous wheat (WW). Soil water at wheat planting following sorghum averaged about 9 in., which is about 3 in. more than the second wheat crop in a WWSF rotation. Soil water at sorghum planting was approximately 1.5 in. less for the second sorghum crop, compared with sorghum following wheat. Grain yield of recrop wheat averaged about 80% of the yield of wheat following sorghum. Grain yield of continuous wheat averaged about 65% of the yield of wheat grown in a four-year rotation following sorghum. Wheat yields were similar following one or two sorghum crops. Similarly, average sorghum yields were the same following one or two wheat crops. Yield of the second sorghum crop in a WSSF rotation averaged 65% of the yield of the first sorghum crop.

Introduction
In recent years, cropping intensity has increased in dryland systems in western Kansas. The traditional wheat-fallow system is being replaced by wheat-summer crop-fallow rotations. With concurrent increases in no-till, is more intensive cropping feasible? Objectives of this research were to quantify soil water storage, crop water use, and crop productivity of four-year and continuous cropping systems.

Procedures
Research on four-year crop rotations with wheat and grain sorghum was initiated at the Tribune Unit of the Southwest Research-Extension Center in 1996. Rotations were WWSF, WSSF, and WW. No-till was used for all rotations. Available water was measured in the soil profile (0 to 8 ft) at planting and harvest of each crop. The center of each plot was machine harvested after physiological maturity, and yields were adjusted to 12.5% moisture.

Soil water
The amount of available water in the soil profile (0 to 6 ft) at wheat planting varied greatly from year to year (Figure 1). Soil water was similar following fallow after either one or two sorghum crops, and averaged about 9 in. across the 15-year study period. Water at planting of the second wheat crop in a WWSF rotation generally was less than that at planting of the first wheat crop, except in 1997 and 2003. Soil water for the second wheat crop averaged more than 3 in. (or about 40%) less than that for the first wheat crop in the rotation. Continuous wheat averaged about 0.7 in. less water at planting than the second wheat crop in a WWSF rotation. Similar to wheat, the amount of available water in the soil profile at sorghum planting varied greatly from year to year (Figure 2.) Soil water was similar following fallow after either one or two wheat crops and averaged about 8.25 in. over 16 years. Water at planting of the second sorghum crop in a WSSF rotation was generally less than that at planting of the first sorghum crop. Averaged across the entire study period, the first sorghum crop had about 1.5 in. more available water at planting than the second crop.

Grain yields
In 2011, wheat yields were below average because of a dry fall and winter (Table 1) Generally, little difference has occurred in wheat yields following one or two sorghum crops. In most years, continuous wheat yields have been similar to recrop wheat yields, but in several years (2003, 2007, and 2009), recrop wheat yields were considerably greater than continuous wheat yields.

A. Schlegel
Summary Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize production of irrigated corn in western Kansas. In 2011, N applied alone increased yields 87 bu/a, whereas P applied alone increased yields 13-19 bu/a. N and P applied together increased yields up to 139 bu/a. This is similar to the past 10 years, where N and P fertilization increased corn yields up to 130 bu/a. Application of 120 lb/a N (with P) was sufficient to produce about 95% of maximum yield in 2011, which was similar to the 10-year average. Application of 80 instead of 40 lb P 2 O 5 /a increased average yields of only 2 bu/a in 2011. Soil organic matter was increased by N and P fertilization. Soil pH was decreased by increased N rates and not affected by P fertilization. Application of 40 lb P 2 O 5 /a was not sufficient to maintain soil test P levels.

Introduction
This study was initiated in 1961 to determine responses of continuous corn and grain sorghum 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 corn from K fertilization was observed in 30 years, and soil K levels remained high, so the K treatment was discontinued in 1992 and replaced with a higher P rate.

Procedures
This field study is conducted at the Tribune Unit of the Southwest Research-Extension Center. Fertilizer treatments initiated in 1961 are N rates of 0, 40, 80, 120, 160, and 200 lb/a without P and K; with 40 lb/a P 2 O 5 and zero K; and with 40 lb/a P 2 O 5 and 40 lb/a K 2 O. The treatments were changed in 1992, when the K variable was replaced by a higher rate of P (80 lb/a P 2 O 5 ). All fertilizers were broadcast by hand in the spring and incorporated before planting. The soil is a Ulysses silt loam. The corn hybrids [Pioneer 33R93 (2002), DeKalb C60-12 (2003) crops. The corn is irrigated to minimize water stress; sprinkler irrigation has been used since 2001. The center two rows of each plot are machine harvested after physiological maturity. Grain yields are adjusted to 15.5% moisture. Soil samples (0-6 in.) were taken following harvest in 2010. Soil test P was determined by two methods; Bray-1 because the historical analyses used this method, and Olsen because of the high pH in some treatments.

A. Schlegel
Summary Long-term research shows that phosphorus (P) and nitrogen (N) fertilizer must be applied to optimize production of irrigated grain sorghum in western Kansas. In 2011, N applied alone increased yields about 50 bu/a, whereas N and P applied together increased yields up to 75 bu/a. Averaged across the past 10 years, N and P fertilization increased sorghum yields more than 60 bu/a. Application of 40 lb/a N (with P) was sufficient to produce about 80% of maximum yield in 2011, which was slightly less than the 10-year average. Application of potassium (K) has had no effect on sorghum yield throughout the study period. Soil organic matter was increased by N and P fertilization. Soil pH was decreased by increased N rates and not affected by P fertilization. Application of 40 lb P 2 O 5 /a was sufficient to maintain soil test P levels.

Introduction
This study was initiated in 1961 to determine responses of continuous grain sorghum grown under flood irrigation to N, P, and K fertilization. The study is conducted on a Ulysses silt loam soil with an inherently high K content. The irrigation system was changed from flood to sprinkler in 2001.

Procedures
This field study is conducted at the Tribune Unit of the Southwest Research-Extension Center. Fertilizer treatments initiated in 1961 are N rates of 0, 40, 80, 120, 160, and 200 lb/a N without P and K; with 40 lb/a P 2 O 5 and zero K; and with 40 lb/a P 2 O 5 and 40 lb/a K 2 O. All fertilizers are broadcast by hand in the spring and incorporated before planting. Sorghum (Pioneer 8500/8505 from 1998-2007and Pioneer 85G46 in 2008-2011 is planted in late May or early June. Irrigation is used to minimize water stress. Furrow irrigation was used through 2000, and sprinkler irrigation has been used since 2001. The center two rows of each plot are machine harvested after physiological maturity. Grain yields are adjusted to 12.5% moisture. Soil samples (0-6 in.) were taken following harvest in 2010. Soil test P was determined by two methods: Bray-1, because the historical analyses used this method, and Olsen, because of the high pH in some treatments.

Results
Grain sorghum yields in 2011 were greater than the 10-year average yields (Table 1).
Nitrogen alone increased yields about 50 bu/a, and P alone increased yields less than 10 bu/a; however, N and P applied together increased yields up to 75 bu/a. Averaged across the past 10 years, N and P applied together increased yields more than 60 bu/a. In 2011, 40 lb/a N (with P) produced about 80% of maximum yields, which is slightly less than the 10-year average. Sorghum yields were not affected by K fertilization, which has been the case throughout the study period.

Results
Corn yields in 2011 were much greater than the long-term average (Table 1). Phosphorus increased yields more than 60 bu/a, which was similar to the long-term average. Application of 80 lb/a P 2 O 5 produced maximum yield in 2011, and 97% of maximum yield was obtained with 40 lb/a P 2 O 5 . Across the eight years of the study, 40 lb/a P 2 O 5 produced 93% of maximum yield.

Alan Schlegel
Summary Phosphorus (P) increased sorghum yields more than 30 bu/a in 2011, which was greater than the long-term average. Application of 80 lb/a P 2 O 5 produced maximum yield in 2011, and 90% of maximum yield was obtained with 40 lb/a P 2 O 5 . Across the eight years of the study, 20 lb/a P 2 O 5 produced ~95% of maximum yield. Soil test P remained relatively constant even without the application of P fertilizer and was considerably increased with P rates of 40 lb/a P 2 O 5 or greater.

Introduction
This study was initiated in 2004 to determine responses of continuous grain sorghum grown under sprinkler irrigation to P fertilization. This study complements a long-term nitrogen (N) and P study by having a wider range of P rates. The study is conducted on a Ulysses silt loam soil with an inherently high potassium (K) content.

Procedures
This field study is conducted at the Tribune Unit of the Southwest Research-Extension Center. Fertilizer treatments are 0, 20, 40, 80, and 120 lb/a of P 2 O 5 . All P fertilizers were broadcast by hand in the spring and incorporated before planting. Treatments were applied to the same plots each year. Nitrogen was uniformly applied to all plots at 200 lb N/a. Sorghum (Pioneer 8500/8505 from 2004-2007and Pioneer 85G46 in 2008-2011 is planted in late May or early June. Hail damaged the 2005, 2008, and 2010 crops. The grain sorghum is irrigated to minimize water stress. The center two rows of each plot are machine-harvested after physiological maturity. Grain yields are adjusted to 12.5% moisture. Soil samples (0-6 in.) were taken following harvest in most years and analyzed for Mehlich-3 P.

Results
Grain sorghum yields in 2011 were greater than the long-term average (Table 1). Phosphorus increased yields more than 30 bu/a, which was greater than the long-term average. Application of 80 lb/a P 2 O 5 produced maximum yield in 2011, and 90% of maximum yield was obtained with 40 lb/a P 2 O 5 . Across the eight years of the study, 20 lb/a P 2 O 5 produced ~95% of maximum yield.

Introduction
As many weed species develop resistance to common herbicide modes of action, labeling new compound novel modes of action becomes even more important. Pyroxasulfone has been exhaustively researched at the Southwest Research-Extension Center in Garden City, KS, for over a decade with the experimental code name KIH 485. Pyroxasulfone is finally expected to be labeled by June of 2012. Saflufenacil was labeled at the beginning of the 2011 growing season. The objective of this study was to measure the effects of various tank mixes of saflufenacil and pyroxasulfone with other known herbicide standards for Palmer amaranth control.

Procedures
Palmer amaranth control was evaluated in the glyphosate-resistant corn variety DKC 64-83 at the Kansas State Research Center located near Garden City, KS. Corn was planted on May 5, 2011, with preemergence herbicides applied within 24 hours of planting. Preemergent application conditions of air temperature, soil temperature, wind speed, relative humidity, and soil moisture were 62ºF, 55ºF, 5 mph, 83%, and adequate, respectively. Soil was Ulysses silt loam, and organic matter, soil pH, and cation exchange capacity (CEC) were 1.4%, 8, and 18.4. All herbicide treatments were applied with a tractor-mounted CO 2 pressurized windshield sprayer calibrated to deliver 20 gpa at 30 psi at 4.1 mph. All plots were treated with 32 oz/a of glyphosate to remove any emerged plants from the plots. Adjuvant and ammonium sulfate (AMS) were added per manufacturer recommendations. The first post-herbicide application was made on June 13, 2011, when corn was 14 in. tall. Air temperature, soil temperature, wind speed, relative humidity, and soil moisture were 78ºF, 68ºF, 7 mph, 58%, and adequate. The second post-application herbicide application was made on June 15, 2011, with air temperature, soil temperature, wind speed, relative humidity, and soil moisture at 72ºF, 70ºF, 5 mph, 26%, and adequate. Trial was established as a randomized complete block design with four replications, and plots were 10 ft by 30 ft. Crop injury and percentage weed control were visually rated.

Results and Discussion
No crop injury was observed. Palmer amaranth was controlled 95% or better with treatments 3, 6, and 7 at 49 days after planting (DAP) compared with 0 to 13% in untreated checks. By 113 DAP, only treatments 6 and 7 had greater than 97% control compared with 0% control in the untreated check (Table 1). Due to extraordinary drought conditions, corn yield varied widely based on when maximal drought stress occurred.
Although the planting date of this trial produced the highest yields of any near this test site, the highest yields still ranged from 40 to 50 bu/a. The primary value of pyroxasulfone is as a control agent for grassy weeds; it also appears to have activity on Palmer amaranth, a small-seed broadleaf weed. Previous work has shown that this result occurs two out of three years and is dependent on herbicide rate and rainfall. This pattern of control is consistent with other grass herbicides. In this study, saflufenacil and pyroxasulfone tank mixes appear to provide Palmer amaranth control. The degree and duration of control appears to be contingent on the rate used. The price of pyroxasulfone has yet to be determined and will not be static over the next several years, but after a few years, market forces will establish its value. When the price is known, the economical rate to use the compound will be more easily determined.

Results and Discussion
No crop injury was observed. Palmer amaranth control 49 DAP was greater than 95% in all but treatments 9, 10, and 14 compared with 0% in untreated checks (Table 1). With the exception of treatments 8, 9, and 10, all treatments provided greater than 93% control by 106 DAP. Although yield data was collected due to drought, yield was too poor for the data to be useful. No preemergence treatment alone produced sufficient control 49 days after planting (DAP). With only one exception, all preemergence treatments followed by a postemergence application provided greater than 95% control 106 DAP. All of these treatments contained more than one herbicide mode of action. Introduction As their patents expire or approach expiration, products are often augmented with newer compounds to extend their useful life in the marketplace. The objective of this study was to determine how rimsulfuron and atrazine effectiveness could be enhanced with various tank mixes of other products.

Procedures
Palmer amaranth control was evaluated in the glyphosate-resistant corn variety DKC 64-83 at the Southwest Research-Extension Center near Garden City, KS. Corn was planted on May 20, 2011, with preemergent herbicides applied within 24 hours of planting under air temperature, soil temperature, wind speed, relative humidity, and soil moisture of 52ºF, 63ºF, 6 mph, 75%, and adequate, respectively. Soil was Ulysses silt loam, and organic matter, soil pH, and cation exchange capacity (CEC) were 1. 4%, 8, and 18.4. All herbicide treatments were applied with a tractor-mounted CO 2 pressurized windshield sprayer calibrated to deliver 20 gpa at 30 psi at 4.1 mph. All plots were treated with 32 oz/a of glyphosate to remove any emerged plants from the plots. Adjuvant and ammonium sulfate (AMS) were added per manufacturer recommendations. The first post-herbicide application was made on June 15, 2011, when corn was 14 in. tall and air temperature, soil temperature, wind speed, relative humidity, and soil moisture were 85ºF, 76ºF, 4 mph, 26%, and adequate, respectively. The second postherbicide application was made on June 29, 2011, with air temperature, soil temperature, wind speed, relative humidity, and soil moisture of 70ºF, 77ºF, 15 mph, 55%, and adequate. Trial was established as a randomized complete block design with four replications and plots were 10 by 30 ft. Crop injury and percentage weed control were visually rated.

Results and Discussion
No crop injury was observed. Palmer amaranth control was 93% or greater with herbicide treatments 3, 7, 9, 10, 17, 20, and 22 at 41 DAP compared with 0% in untreated checks (Table 1). Only treatments 7, 10, 18, 21, and 22 had greater than 95% control 69 DAP compared with 0% control in the untreated check. All of these treatments contained atrazine. Treatments 18, 19, and 22 provided 95% or greater control of Palmer amaranth 98 DAP (data not shown). Although yield data were gathered, they were not included because the highest-yielding treatment produced only from 28 to 50 bu/a due to historic drought conditions. These highest-yielding treatments also had the best weed control 98 DAP (data not shown).

Introduction
In a 2011 long-term experiment to measure the dose-response relationship of irrigation and corn grain yield, corn production was reduced by a severe drought. Corn biomass and leaf area decreased as irrigation decreased, causing late-season Palmer amaranth growth. Previous work in hail-injured corn showed that reductions in leaf area index (LAI) also allowed late-season Palmer amaranth growth (Currie and Klocke, 2008). Therefore, the objective of this work was to measure corn differentially injured by drought as indexed by leaf area.

Procedures
Corn was grown in three locations where the objective was to maintain weed-free conditions. For the five years prior to 2011, weed control was pursued with aggressive herbicide tank mixes. In 2011, corn first received a preemergence application of glyphosate, atrazine, isoxaflutole, dimethenamid, and saflufenacil at 1, 1.7, 0.031, 0.78, and 0.08 lb ai/a, respectively, followed by postemergence application of fluroxypyr, glyphosate, S-metolachlor, and tembotrione at 0.13, 1, 1.43, and 0.082 lb/a, respectively. Additional postemergence applications of glyphosate at 0.75 lb/a were applied, as needed, to maintain weed-free conditions at canopy closure. The treatments, replicated four times, were 100, 84, 71, 55, 42, and 30% of what locally derived models predicted for non-rate-limited irrigation. As a result, the net irrigation amounts were 18, 14, 10, 7, 4, and 1 in./a across irrigation treatments, which resulted in 25, 20, 16, 13, 11, and 7 in. of total water use per acre (evapotranspiration), respectively. Total water use was based on soil water measurements up to 8 ft, total in-season rainfall, and total net irrigation. Corn populations for each treatment decreased as level of irrigation decreased . Populations were 32,000, 27,000, 24,500, 22,000 and 9,500, plants/a, respectively.These populations were based on previous models for the level of irrigation to be applied. Corn LAI was measured as described in a previous study (Currie and Klocke, 2008). Palmer amaranth biomass samples were taken at corn harvest.

Results and Discussion
The fully irrigated corn yielded from 178 to 203 bu/a. Grain yield decreased linearly at all locations, to a minimum of 0 to 3.5 bu/a when irrigated with less than 30% of full irrigation requirements. Palmer amaranth biomass was from 9 to 38 lb/a in fully irrigated corn. Palmer amaranth biomass increased from 1.5-to 4-fold as irrigation decreased to 60% of full irrigation. At all three locations, when irrigation was less than 50% of full irrigation requirements, Palmer amaranth biomass increased from 6-to 31-fold compared with fully irrigated corn; however, when irrigation was below 30% of full irrigation requirements, Palmer amaranth biomass was 51 to 82 lb/a. Although corn populations were reduced to match reduced irrigation levels, reducing crop water stress enough to prevent corn leaf loss due to drought was impossible. Severe reduction in the corn canopy allowed late-season Palmer amaranth to emerge.
In our previous study, simple linear models of corn LAI reduced by hail predicted corn yield loss well, with R-squared values well above 0.94 (Currie and Klocke, 2008). Simple linear models of LAI were also predictive of corn yield loss in this study, with R-squared values greater than 0.99. We advise using this data with caution because although it is based on two locations, we used regressions of only 3 points; therefore, the results should be considered only a starting point for future research. Although the previous work showed a strong linear relationship between corn LAI influenced by hail injury and Palmer amaranth biomass, no relationship could be shown using this limited dataset for corn injured by drought stress. When corn was irrigated with more than 60% of full irrigation, it was able to compete with Palmer amaranth. With irrigation levels from 30 to 50%, Palmer amaranth was able to utilize the remaining water better than the corn. When irrigation was below 30%, drought severely reduced both weed and crop growth.

Introduction
Kochia has developed resistance to glyphosate herbicide in many parts of the Great Plains. Detailed studies of the basic biology of this emerging weed problem are scarce.
Timing of control measure applications is largely influenced by date of emergence and subsequent weed size, but little is known about this aspect of kochia biology. Therefore, the objective of this study was to measure the timing and duration of kochia seedling emergence.

Results and Discussion
Total season population densities varied among locations and ranged from as few as 10 to almost 332,000 seedlings/m 2 (Table 1). Earliest observed emergence occurred soon after March 2 across locations in 2010 and occurred even earlier in 2011 (Table  2). Although the calendar dates shift from March to April as location moves from south to north, the growing degree days (GDD) for 10% cumulative kochia emergence based on air temperatures since January 1 revealed that fewer GDD were needed before seedling emergence occurred in the north than in the south. This result may indicate a lower critical temperature for kochia in more northern latitudes. In general, the rate of kochia emergence was slower in cropland than in non-cropland environments. From 70 to 95% of the kochia seedlings emerged between the first two observation dates across all locations. High seedling emergence very early in the season emphasizes the need for early weed control, and the high number of seedlings that appear in the second flush (from 5 to 30% of the total population) emphasizes the need for extended periods of early season kochia management.

Introduction
The widespread presence of glyphosate-resistant kochia throughout western Kansas underscores the need for alternatives to glyphosate for weed control in corn. Our objective was to compare the performance of several herbicide treatments other than glyphosate for kochia control in no-till corn.

Procedures
Experiments were conducted on grower fields (dryland) near Levant, Park, Phillipsburg, and Shields, KS, in 2011. Each field was naturally infested with kochia that was subsequently confirmed as resistant to glyphosate. Experimental areas received a preplant burndown treatment prior to corn planting, and treatments were applied preemergence within 2 days after planting (hybrid of grower's choice) by the farm operator. Spray volume was 15 gal/a at Levant and 12.7 gal/a at Park, Phillipsburg, and Shields. Postemergence treatments were applied at the V5 corn growth stage at Levant when kochia was 1 to 6 in. tall, V4 corn growth stage at Park when kochia was 3 to 6 in. tall, V2 corn stage at Phillipsburg when kochia was 0.5 to 1.5 in. tall, and V4 growth stage at Shields when kochia was 3 to 4 in. tall. Kochia density ranged from 5 to 10 plants/yd 2 at Park and more than 100 plants/yd 2 at Phillipsburg. Treatment costs include herbicides and adjuvants (10% over dealer cost), but not application or program discounts or rebates. Corn in the Park and Shield trials was harvested for silage because of drought, and grain yields of the Levant and Phillipsburg trials are not reported.
applied mixtures of Balance Flexx plus Aatrex 4L at 4 + 20 oz/a, Lumax at 2.5 qt/a, and Degree Xtra at 3.0 qt/a controlled kochia 90% or greater (Table 2). Clarity + 2,4-D LV4 was slightly less effective at 86%. Postemergence-applied Laudis (3 oz/a) or Impact (0.75 oz/a) mixed with 8 oz/a Aatrex 4L along with AMS and MSO provided 87% kochia control. Mixing Aatrex 4L with Laudis enhanced control significantly compared with Laudis alone. Kochia control with most treatments, especially those without atrazine, declined significantly at the end of the season compared with midseason ratings (data not shown); only Balance Flexx plus Aatrex 4L and Lumax treatments maintained control above 80%. Although postemergent applications of Laudis or Impact plus Aatrex 4L and MSO were similarly effective as the most effective preemergence treatments at mid-season, end-of-season control with those two treatments was less than 65%. Herbicide treatment costs ranged from as low as $7.91 up to $42.75 per acre. Correlation between treatment cost and kochia control was poor (r = 0.35 or less) at each rating. The greatest and most consistent season-long control averaged across experiments was achieved with Balance Flexx + Aatrex at 4 + 20 oz/a at a cost of $21.30/a. Lumax provided similar season-long control as Balance Flexx + Aatrex but at considerably higher cost.
Lack of complete or nearly complete kochia control with the preemergence herbicides tested in this study supports the recommendations of K-State weed scientists that producers use a preplant or preemergence herbicide treatment followed by an in-crop postemergence herbicide treatment to obtain maximum kochia control.

Introduction
Confirmed glyphosate resistance in multiple kochia (Kochia scoparia) populations in western Kansas prompted the need to investigate alternatives to glyphosate for control of kochia.

Procedures
Separate field trials comparing standardized preemergence or postemergence herbicide treatments were conducted at one or more locations in Colorado, Kansas, Montana, Nebraska, and Wyoming to evaluate kochia control effectiveness in spring fallow or prior to crop planting. Only one of the two trials (PRE or POST) was conducted at some locations. Preemergence herbicides were applied in March or April 2011, depending on location, and postemergence treatments were applied along with appropriate adjuvants when the majority of kochia plants were 1-4 in. tall.
locations, making time comparisons difficult because of different numbers of trials with similar times of evaluation. Control percentages between most treatments varied widely both within locations and especially between locations, likely because of differing environmental conditions. Kochia control with Roundup PowerMax (glyphosate) at 32 oz/a was less than 30% in each of four Kansas trials, 43% in one Colorado trial, 82% in one Montana trial, and 93 and 96% in one Nebraska and a second Colorado trial.