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Number 319 September 30, 2011

1. Crop Water Allocator: Western Kansas-based tool for limited irrigation decision-making_ 1

2. Wheat stubble cutting height affects row crop yields in no-till rotations _______________ 2

3. Controlling annual weeds with fall-applied herbicides ahead of corn and sorghum ______ 5

4. Comparative Vegetation Condition Report: September 13 – 26 ______________________ 6 1. Crop Water Allocator: Western Kansas-based tool for limited irrigation decision-making Where irrigation water is limited, irrigators have difficult decisions to make about which crops to grow and what rotation systems will work best. Crop yields at various water amounts, production costs, and crop prices all figure into the decision. A good decision-making tool to help sort out these choices for western Kansas conditions is the Crop Water Allocator (CWA), developed by K-State engineers and agronomists. The CWA program can be downloaded from www.mobileirrigationlab.com The data for the yield vs. irrigation and precipitation calculations were developed from field research plots using conventionally tilled management in western Kansas, which is why it is best used by irrigators specifically in that region. The CWA calculates net economic returns from many combinations of crops and irrigation allocations among crops, then ranks the net returns from maximum to minimum values. Users can select a range of input variables such as rainfall, production costs, commodity prices, irrigation costs, irrigation efficiency, and maximum yields. The user needs to enter input values for the execution of CWA: geographic location, soil type, irrigation costs, irrigation application efficiency, annual precipitation, annual irrigation amount, land split, commodity price, and maximum yield. Crop production costs can come from the CWA user or from the software’s internal default production costs from Kansas State University’s agricultural economists (www.agmanager.info). The CWA determines crop yields from irrigation and precipitation (11 to 24 in.) for alfalfa, corn, soybean, grain sorghum, wheat, and sunflower. CWA assumes that production inputs other than irrigation do not limit yields. Crop management that does not meet best management practices criteria will not achieve the predicted results of CWA.

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The user of CWA can choose a rotation scheme for five possible land splits: 50%-50%, 75%-25%, 33%-33%-33%, 50%-25%-25%, or 25%-25%-25%-25%. The user can choose one land split for each execution of CWA or hold land split constant as other inputs are changed. The program will assign every combination of every selected crop to each part of the land split. More crops than land splits can be selected for CWA analysis. One crop may be in more than one part or in all parts of the rotation. CWA then allocates water to each crop in each combination of selected crops for the rotation. Net return results from all combinations of crops in each part of the rotation and irrigation are “stacked” from maximum to minimum. The user can scroll through approximately 20 of the largest net return results displayed on the output screen. Some of the crop combinations in the rotation may not be feasible for users even though certain crops have more net return than others. For example, soybean in all parts of the rotation would not be feasible because continuous soybean is not recommended. In addition to choosing combinations of crops for rotation, decisions about how much water to apply to each crop comes into play. For example, corn needs to be irrigated to full yields because of the high economic return whereas other crops in the rotation such as sorghum and wheat can receive limited water and still respond well. -- Loyd Stone, Soil and Water Conservation stoner@ksu.edu -- Norm Klocke, Water Resources Engineer, Southwest Research-Extension Center nklocke@ksu.edu -- Troy Dumler, Agricultural Economist, Southwest Research-Extension Center tdumler@ksu.edu

2. Wheat stubble cutting height affects row crop yields in no-till rotations Producers using a no-till wheat/row crop/fallow rotation may find that row crop yields in such a rotation are higher (in years with relatively normal weather) when the wheat stubble height is taller. K-State research in western Kansas by Lucas Haag, Agronomy graduate student, and Alan Schlegel, Agronomist-In-Charge at the Southwest Research-Extension Center-Tribune, has found that corn grain yields increased as stubble height increased. Grain sorghum yield response to stubble height was less apparent, but exhibited a response to moderately higher cutting heights. Wheat residue provides numerous benefits, including evaporation suppression, delayed weed growth, improved capture of winter snowfall, and reduced soil erosion. Stubble height affects wind velocity profile, surface radiation interception, and surface temperatures, all of which will

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reduce evaporation potential and increase winter snow catch. Taller wheat stubble is also beneficial to pheasants in postharvest and overwinter fallow periods. Using stripper headers provides taller wheat stubble than previously attainable with conventional headers. In theory, increasing wheat cutting heights or using a stripper header should further improve the effectiveness of standing wheat stubble. The purpose of our research was to evaluate the actual effect of wheat stubble height on subsequent summer row crop yields.

Procedures Studies were conducted from 2007 through 2010 at the Southwest Research-Extension Center dryland station near Tribune. Corn and grain sorghum were planted into standing wheat stubble of three heights: short, optimal, and stripped. * The short cut treatment was half of optimal cutter bar height. * Optimal cutter bar height is the height necessary to maximize both grain harvested and standing stubble remaining (typically two-thirds of total plant height). * The third treatment was stubble remaining after stripper header harvest. In 2007, these heights were 7, 14, and 22 inches. In 2008, heights of 10, 20, and 30 inches were obtained. In 2009 the heights were 7, 14, and 23 inches. In 2010 the stubble measured 8, 16, and 25 inches. Corn was seeded at the rate of 15,000 seeds per acre, and grain sorghum was seeded at the rate of 33,000 seeds/acre. In 2010 the sorghum plots were split and an additional seeding rate of 41,000 seeds/a was added to the study. Nitrogen was applied to all plots at a rate of 80 to 100 lb/acre. Starter fertilizer (10-34-0) was applied in-row at rates of 7 and 9 gal/a for corn and sorghum, respectively. Plots measured 40 ft × 60 ft. Soil water measurements were obtained by neutron attenuation to a depth of 6 feet in 1-foot increments at seeding and harvest to determine water use and water use efficiency (WUE).

Results: 2007-2010 Over the 4 years 2007-2010, corn grain yield increased from 80 to 92 bu/acre as stubble height increased. Increased grain yields are the result of the effect of stubble height on one primary yield component, kernels per ear, which increased with increasing stubble height from 467 for the low cut to 521 for the stripped stubble treatment. Another key yield component, ear population, also increased numerically with increasing stubble height, suggesting that increasing stubble height also may reduce in-season plant mortality and ear abortion. Corn grown in stripped or optimal-cutter-bar-height stubble resulted in higher WUE, which increased from 305 lb/inch in short-cut stubble to 361 lb/inch in the stripped stubble treatment. Over the 4 years, sorghum grain yields exhibited a quadratic response to stubble height, with optimal-cutter-bar-height stubble producing grain yields 4 to 5 bu/acre higher than either the stripped or short-cut treatment. An examination of yield components revealed that kernels per head generally increased with increasing stubble height. Although no statistical differences were observed, heads per plant exhibited a positive response to increasing stubble height. Future efforts in this study will involve more emphasis on yield components, specifically tillers per plant, in an effort to identify any interaction between tillering and the production environment created by stripped stubble.

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Data from prior years suggested that sorghum planted into stripped stubble was yielding less than sorghum planted into optimal-cutter-bar-height stubble due to reduced tillering. The addition of the 41,000 seeding rate was designed to further investigate this possibility. Interestingly, in 2010 the increased seeding rate resulted in only a very small increase in plant and head population.

Corn response to wheat stubble height: 2007-2010 Stubble height

Yield (bu/acre)

Plant population

(plants/acre)

Ear population (ears/acre)

Kernel weight (oz/1,000)

Kernels per ear

Water use efficiency (lb/inch)

Low 80.3b 15,500 15,100 10.33 467b 305b Optimal (high) cutter bar height

89.9a 15,400 15,400 10.54 504a 350a

Stripped 92.0a 15,500 15,700 10.42 521a 361a

Grain Sorghum response to wheat stubble height: 2007-2010 Stubble height

Yield (bu/acre)

Plant population

(plants/acre)

Head population

(heads/acre)

Kernel weight (oz/1,000)

Kernels per head

Water use efficiency (lb/inch)

Low 102.9 19,200 50,200 0.91 2073 413 Optimal (high) cutter bar height

107.4 18,900 51,900 0.92 2069 432

Stripped 101.9 18,300 50,000 0.88 2109 419

Conclusions Increasing stubble height has improved subsequent corn grain yields and WUE. The impact of stubble height on grain sorghum yields is less apparent at this time and requires further study. Surprisingly, this study has found little impact of stubble height on profile available soil water. This is in direct contrast to other studies and anecdotal field observations. Corn grain yield differences in the absence of differences in available soil water at planting indicate a more pronounced impact of stubble harvest height on in-season plant-water dynamics than previously thought. Additional years of observation are needed to identify any potential effect of stubble height on the yield components of grain sorghum and to provide a more robust dataset across multiple years in which to evaluate the effects of stubble height on soil water storage. – Steve Watson, Agronomy e-Update Editor Adapted from K-State Southwest Research-Extension Center Field Day 2011, SRP-1052, pages 37-42, available at your local county Extension office, or at: http://www.ksre.ksu.edu/library/crpsl2/srp1052.pdf

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3. Controlling annual weeds with fall-applied herbicides ahead of corn and sorghum With row crop harvest underway, it’s time to start planning your fall herbicide applications to control winter annual broadleaf weeds and grasses ahead of grain sorghum or corn. Fall applications during the last couple of weeks of October and through November can greatly assist control of difficult winter annuals and should be considered when performance of spring preplant weed control has not been adequate. There are several options. For residual herbicides, producers could use atrazine. Atrazine is labeled in Kansas for fall application over wheat stubble or after fall row crop harvest anytime before December 31, as long as the ground isn’t frozen. Consult the atrazine label to comply with maximum rate limits and precautionary statements when applying near wells or surface water. No more than 2.5 lbs of atrazine can be applied per acre in a calendar year on cropland. One half to two pounds (maximum)/acre of atrazine in the fall, usually with 1 to 2 pint/acre of 2,4-D LV4 or LV6 added, can give good burndown of winter annual broadleaf weeds -- such as henbit, Virginia pepperweed, prickly lettuce, field pansy, evening primrose, and marestail -- and small non-tillered winter annual grasses. Atrazine residual should control germinating winter annual broadleaves and grasses. When higher rates of atrazine are used, there should be enough residual effect from the fall application to control early-spring germinating summer annual broadleaf weeds such as kochia, lambsquarters, wild buckwheat, and Pennsylvania smartweed. Atrazine activity is enhanced by the use of adjuvants. Review atrazine and tankmix partner labels for best adjuvant choice. Tank mixing 2,4-D with atrazine enhances control of all broadleaf species. It is especially important for common dandelion, henbit, marestail, and prickly lettuce control. The low-volatile ester formulations should be used, as they tend to be more potent than amine formulations, pound for pound. While it is always important to manage herbicide drift, herbicide applications made after fall frost have less potential for drift problems. Marestail is a growing problem in Kansas that merits special attention. Where corn or grain sorghum will be planted next spring, fall-applied atrazine plus 2,4-D has been very effective on marestail rosettes, and should have enough residual activity to kill marestail as it germinates in the spring. Atrazine alone will not be nearly as effective postemergence on marestail as the combination of atrazine plus 2,4-D. Sharpen is very good on marestail, and can be tankmixed with 2,4-D, atrazine, or glyphosate. If the spring crop will be corn, other residual herbicide options include an ALS herbicide such as Autumn or Basis. ALS-resistant marestail will survive Autumn or Basis treatment if applied alone. For burndown, producers should mix in 2,4-D and/or glyphosate. Aim and Rage D-Tech are other non-residual, contact herbicide options for fall application. Winter annual grasses can also be difficult to control at times, depending on the stage of growth and atrazine rate. For downy brome control, 2 lb/acre of atrazine plus crop oil concentrate (COC)

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has given excellent control, whereas 1 lb/acre has given only fair control. Volunteer wheat and brome species that have tillered will likely not be controlled even with a 2 lb rate. Adding glyphosate to that mixture will control volunteer wheat, annual bromegrasses, and other grassy weeds. Atrazine antagonizes glyphosate, so if the two are used together, producers should use a full rate of glyphosate (0.75 lb ae). The tankmix should include AMS as an adjuvant. If fall treatments control volunteer wheat, winter annuals, and early-emerging summer annuals right up to planting corn or sorghum, then at planting time only a light preplant tillage or a preemerge grass and broadleaf herbicide application with glyphosate or paraquat will be needed to catch newly emerged weeds. Soils will be warmer and easier to plant where winter weeds were controlled in fall. -- Curtis Thompson, Weed Management Specialist cthompso@ksu.edu 4. Comparative Vegetation Condition Report: September 13 – 26 K-State’s Ecology and Agriculture Spatial Analysis Laboratory (EASAL) produces weekly Vegetation Condition Report maps. These maps can be a valuable tool for making crop selection and marketing decisions. Two short videos of Dr. Kevin Price explaining the development of these maps can be viewed on YouTube at: http://www.youtube.com/watch?v=CRP3Y5NIggw http://www.youtube.com/watch?v=tUdOK94efxc The objective of these reports is to provide users with a means of assessing the relative condition of crops and grassland. The maps can be used to assess current plant growth rates, as well as comparisons to the previous year and relative to the 21-year average. The report is used by individual farmers and ranchers, the commodities market, and political leaders for assessing factors such as production potential and drought impact across their state. The maps below show the current vegetation conditions in Kansas, the Corn Belt, and the continental U.S, with comments from Mary Knapp, state climatologist:

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Map 1. The Vegetation Condition Report for Kansas for September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that photosynthetic activity continues to decline. More vegetation is entering dormancy, so vegetative production has begun to decline.

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Map 2. Compared to the previous year at this time for Kansas, the current Vegetation Condition Report for September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that only the Northwestern Division has a higher level of photosynthetic activity. Generally good conditions were more prevalent last year, resulting in more dramatic differences particularly in the Southeastern Division.

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Map 3. Compared to the 22-year average at this time for Kansas, this year’s Vegetation Condition Report for September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that the Southwestern Division continues to be much below average in terms of photosynthetic activity. Some winter wheat emergence is showing in the Northwestern Division as increased photosynthetic activity. Also, some enhanced biomass production can be seen in Cowley and Chautauqua counties in response to early September rainfall.

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Map 4. The Vegetation Condition Report for the Corn Belt for September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that photosynthetic activity is declining as crops mature. Highest activity levels are in the Upper Midwest, as cooler temperatures have prevailed.

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Map 5. The comparison to last year in the Corn Belt for the period September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that the greatest departures are found in the region from northern Iowa through northern Illinois and into Ohio. Harvest is running behind average as cool weather has slowed field drying. Also, in Iowa some flooded areas have been seeded to winter crops to reduce erosion. This will show as enhanced photosynthetic activity, compared to last year.

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Map 6. Compared to the 22-year average at this time for the Corn Belt, this year’s Vegetation Condition Report for September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that a higher-than-average level of photosynthetic activity continues to dominate the northern portions of the Corn Belt. Despite recent dry weather, the milder temperatures and favorable rainfall have favored enhanced photosynthetic activity.

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Map 7. The Vegetation Condition Report for the U.S. for September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that continued photosynthetic activity can be seen in the Mountain West, and along the Pacific Northwest. Lower photosynthetic activity can be seen from Georgia to North Carolina, as well as in the Central Plains from southern Kansas to Texas. In these regions, moderate to extreme drought conditions prevail.

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Map 8. The U.S. comparison to last year at this time for the period September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows that reduced photosynthetic activity can be seen into Missouri and Arkansas. These areas have experienced much less favorable conditions this year as the Southern drought area continues to expand.

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Map 9. The U.S. comparison to the 22-year average for the period September 13 – 26 from K-State’s Ecology and Agriculture Spatial Analysis Laboratory shows the drought impacts in the Southern Plains and the Atlantic Coast, from Georgia to North Carolina. In New England, particularly Massachusetts, the reduced photosynthetic activity is primarily a result of flooding from the earlier tropical systems. Note to readers: The maps above represent a subset of the maps available from the EASAL group. If you’d like digital copies of the entire map series please contact us at kpprice@ksu.edu and we can place you on our email list to receive the entire dataset each week as they are produced. The maps are normally first available on Wednesday of each week, unless there is a delay in the posting of the data by EROS Data Center where we obtain the raw data used to make the maps. These maps are provided for free as a service of the Department of Agronomy and K-State Research and Extension. -- Mary Knapp, State Climatologist mknapp@ksu.edu -- Kevin Price, Agronomy and Geography, Remote Sensing, Natural Resources, GIS kpprice@ksu.edu -- Nan An, Graduate Research Assistant, Ecology & Agriculture Spatial Analysis Laboratory (EASAL) nanan@ksu.edu

These e-Updates are a regular weekly item from K-State Extension Agronomy and Steve Watson, Agronomy e-Update Editor. All of the Research and Extension faculty in Agronomy will be involved as sources from time to time. If you have any questions or suggestions for topics you'd like to have us address in this weekly update, contact Steve Watson, 785-532-7105 swatson@ksu.edu, or Jim Shroyer, Research and Extension Crop Production Specialist and State Extension Agronomy Leader 785-532-0397 jshroyer@ksu.edu