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terminating the remainder of the stand. Consider these two scenarios.

1) If the stand last fall was considered good (70-100% alfalfa) and the field was partly killed over winter and the remaining part will be sprayed out this spring, then it should be considered a good stand for purposes of determining N credits.

2) If the stand last fall was considered good (70-100% alfalfa) and the field was partly killed over winter BUT a first cutting is taken before spraying, then the stand counts after first cut will dictate N credits.

The same reasoning applies when determining N credits for winter-killed red clover. First-year N credits for red clover are 80% of the alfalfa N credit for similar stands.

If there is concern about estimating N credits after win-ter-killed alfalfa then a pre-sidedress nitrate test (PSNT)

Volume 26 Number 3 - - University of Wisconsin Crop Manager - - March 28, 2019

Contents

Nitrogen Credits Following Winter-Killed Alfalfa ..............................................................9

Corn Response To Banded Fertilizers At Planting .............................................................................10

2019 Wisconsin CCA Of The Year, Todd Prill ...............11

New Video: Soybean Cyst Nematodes, Testing For Resistant Populations .................................11

Corn Seed Survival: An Update ......................................11

The Corn Yield Gap In Wisconsin ...................................13

Video: POST-Emergence Pigweed Control with Contact Herbicides in Soybeans ..........14

Nitrogen Credits Following Winter-Killed AlfalfaCarrie Laboski, Professor and Extension Soil Fertility/Nutrient Management Specialist, UW-Madison

Throughout much of the state there is concern about alfalfa winter-kill. Based on the amount of winter-kill in a field, some producers may decide to terminate the alfalfa stand and plant corn instead. It is important to remem-ber that alfalfa N credits should still be taken for this year’s corn crop.

Alfalfa N credits are based on soil texture (medium-/fine-textured or sands/loamy sands), amount of re-growth at the time of stand termination, and number of plants per square foot (Table 1). The method of stand termination (herbicide vs tillage) and time of termination (fall vs spring) do not affect N credits. Where N credits fol-lowing winter-killed alfalfa may differ from typical stand termination methods is related to decisions surrounding whether or not a first cutting of alfalfa is taken prior to

Table 1. First-year alfalfa N credits.

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were seen at Arlington, Fond du Lac and Marshfield. One more year of research will be conducted during 2019.

The response of corn grain yield to starter fertilizer has been studied extensively in the United States, but the specific combinations of environmental conditions and agronomic factors that result in consistent responses re-main unclear. An overall goal of this project is to predict when and where banded fertilizer will provide an eco-nomic return for the farmer. For each replicate soils were sampled and tested for nutrients. At the V5-V6 stage of growth, plants from each hybrid were sampled and tis-sue tests determined plant nutrient concentrations.

Further Reading

Bundy, L.G., and T.W. Andraski. 1999. Site-Specific Factors Affecting Corn Response to Starter Fertilizer. Journal of Production Agriculture 12:664-670.

Additional data:

and be used to confirm the N credits. For more infor-mation on using the PSNT see Chapter 5 in UWEX Pub-lication A2809Nutrient application guidelines for field, vegetable, and fruit crops in Wisconsin.

Corn Response To Banded Fertilizers At PlantingDr. Joe Lauer, UW-Madison Agronomy and Extention State Corn Specialist

Banding fertilizer around the corn seed during planting is a common practice in the northern Corn Belt. Corn planting is frequently delayed in this region due to cold, wet soils, which result in slow root growth and limited uptake of nutrients during early developmental stages.

The last major evaluation of banded fertilizer in Wiscon-sin was conducted between 1995 and 1997 (Bundy and Andraski, 1999). Results indicated that full-season corn hybrids increased grain yield with banded fertilizer when planted late. Since then significant production changes have occurred including higher yields using transgenic crops, improved planting machinery and implements, and continued increases in soil nutrient levels. Growers question whether starter fertilizer is even necessary for modern corn hybrids and production practices, yet, often it is applied as “insurance.” Our objective was to evaluate the agronomic response of corn to banded fertilizer.Plots were established at 11 locations (Arlington, Janesville, Montfort, Fond du Lac, Galesville, Hancock, Marshfield, Chippewa Falls, Seymour, Valders, and Coleman). Fer-tilizer treatments included: 1) an untreated check, 2) seed-placed fertilizer (10-34-0-1(Zn)) applied in the seed furrow at 4.1 gal/A, and 3) starter fertilizer (9-11-30-6(S)-1(Zn)) applied at 200 lb/A as a band 2 in. to the side of the row and 2 in. below the seed. Split-plots were eight to sixteen corn hybrids ranging in RM by 5-d increments from 80 d- to 115 d-RM. An emphasis was placed upon longer-season hybrids at each location and selection of hybrids differing in emergence vigor. Corn was harvested and yields determined mechanically from the center two rows of each four-row plot.

During 2017 and 2018 across all locations, significant differences were found for fertilizer treatment (Figure 1). Overall, starter fertilizer produced greater grain yield than seed-placed fertilizer and the untreated check. On average starter fertilizer (228 bu/A) increased grain yield up to 2.4% more than seed-placed fertilizer (224 bu/A) and the untreated check (223 bu/A). During 2017 and 2018, 5 of 11 locations had a significant response to fertilizer treatment. Consistent response across locations

Figure 1. Corn grain yield response to banded ferti-lizer. Values are are derived from 578 GxE means and averaged across 2017 and 2018. Research is funded by the Wisconsin Fertilizer Research Council.

Table 1. Corn grain yield (bu/A) response to banded fertilizer during 2017.

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2019 Wisconsin Cca Of The Year, Todd PrillBryan Jensen, UW Extension and IPM Program

Please join the WI CCA Board in congratulating Todd Prill as the 2019 Wisconsin CCA of the Year!

Todd lives in Chippewa Falls and graduated from UW River Falls. He has over 22 years of crop advising experi-ence and received his CCA in 1997. Todd recently started working for the Department of Natural Resources but previously was an independent crop consultant offer-ing a full-service program including crop scouting, crop management, pest management, as well as nutrient management planning. The crops he consulted with included forages, corn, soybean, small grains, fruits, vegetables and hops. Todd has also been employed by UW-Extension and with the local County Land Conserva-tion Department.

Todd is a Comprehensive Nutrient Management Plan-ner and Technical Service Provider. He has support-ed several UW Extension County Offices with manure, nutrient management, vari-able rate liming, corn, alfalfa and malting barley research plots. He has also been involved with the Chippewa Valley Forage Council as a member and serves on the board of directors. Todd has

also provided monthly crop reports to area newspapers to help extend his knowledge to the public.

Todd has been an advocate for agriculture by taking time to speak to several organization including the Chippewa Falls Leadership Program and the Chippewa Falls Cham-ber of Commerce. Todd has served two full terms on the Wisconsin CCA Board which included two terms as Chair. He is currently a member of the CCA Test Review Com-mittee.

Please take the time to congratulate Todd the next time you see him!

New Video: Soybean Cyst Nematodes, Testing For Resistant PopulationsDr. Ann Macguidwin, Plant Pathology Department UW Madison

An accurate profile of the types and numbers of SCN is important for explaining damage to the current crop, predicting damage to future crops, and selecting appro-priate measures to keep nematode pests from reaching damaging levels. This video shows how a HG test is con-ducted at the University of Wisconsin-Madison. The assay service identifies plant parasitic nematodes to the genus level and estimates their potential to cause yield loss.

https://www.youtube.com/watch?v=f-TFcyC8Hd4

Corn Seed Survival: An UpdateDr. Joe Lauer, UW-Madison Agronomy and Extention State Corn Specialist

After a corn seed is planted, it is a wonder that the seed can survive and return 400 to 600 fold or more. If Wiscon-sin’s cool, wet spring soils do not kill the plant through imbibitional chilling, then seed rotting pathogens or hungry insects can attack and kill the seed. Once the plant emerges, it is subject to even more biotic and abi-otic stresses that can often kill the plant. Even manage-ment operations like wheel traffic and cultivator blight can inflict significant harm. It is a wonder …

I often get the question, “How much seed survives to produce grain yield?” The question is motivated by the fact that seed costs have risen dramatically in the bio-tech era of corn hybrid development (1996 to present). Some of the rising cost of seed is due to growers plant-ing fields to higher plant densities. Between 1982 and 2017, growers in IA, IL, IN, MN, and WI have increased

Table 2. Corn grain yield (bu/A) response to banded fertilizer during 2018.

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plant population at the rate of 261 to 309 plants/A*yr (USDA-NASS, click https://quickstats.nass.usda.gov . In our experiments, the corn plant density that produces maximum yield has been increasing over time at the rate of 260 plants/A*yr. Since both seed cost and field plant density are increasing, growers are increasingly concerned about how much seed actually survives to emerge and grow into a plant that produces grain yield. In a previous article I summarized the effects of planting date and environment on corn seed survival (click http://wisccorn.blogspot.com/2014/04/B050_3.html .) This arti-cle adds more data to the discussion and looks at recent trends in corn seed survival.

However, most of the rising seed cost is due to the use of bio-engineered traits in modern corn hybrids (USDA-ERS, click http://wisccorn.blogspot.com/2018/01/B092.html ). In the 1990s, a high performing adapted corn hybrid cost about $25 to $30/A ($80 to $125 per 80K bag or $1.00 to $1.56 per 1000 seeds). Today, typical retail seed prices are $100 to $150/A ($250 to $350 per 80K bag or $3.13 to $4.34 per 1000 seeds).

Prior to 2008, we planted corn hybrids in UW trials by over-seeding and hand-thinning back to a uniform plant density. In 2008, we purchased a precision plot planter and dropped a uniform 34,100 seeds/A at every test site during the 2008 to 2015 planting seasons. In the winter of 2015, we had the planter refurbished and upgraded with new software set to drop 34,850 seeds/A since then. At harvest, plant population was measured on ~10% of the plots. All data collected since 2008 (N= 12,036 plots) were used in the analysis.

Seed survival in the traditional corn hybrid trials where chemical seed treatments are used, averaged 91% (Figure 1), and depended upon environment (year and location), cropping system, and seed company. Seed survival during 2012 (drought) was lowest at 82%, while seed survival was highest at 95% during 2009 (wet spring). In organic trials where conventional chemical seed treatments cannot be used, seed survival was lower averaging 83%. Seed survival was lowest at 68% during 2008, while seed survival was highest at 91% during 2009, 2014 and 2018.

Within the UW Corn Hybrid Evaluation program we have tested over 200 unique seed treatment combinations. However, there is no strong trend for seed survival im-provement over time in the traditional trials, while there seems to be some improvement in the organic trials.

Seed survival averaged 90% at test sites in northern Wisconsin, and 94% in southern Wisconsin (Table 1). Marshfield and Seymour had seed survival rates of 88 to 89%. Both Chippewa Falls and Hancock are sandy sites

and had low seed survival (90%). Lancaster seed survival was lower due to tillage issues that caused crusting in many years. Arlington and Fond du Lac had the greatest seed survival at 96%.

The choice of seed company also had a significant effect on seed survival. In the traditional trials, one company had a seed survival rate of 82%, while another company had a survival rate of 97% for a range of 15% (data not shown). In the organic trials, one organic seed company had a seed survival rate of 72%, while another averaged 86% for a range of 14% among companies. This range in company performance is likely due to choice of seed treatment and seed quality effects.

There are numerous factors that influence corn seed sur-vival including hybrid, soil type, seed treatment, tillage system, cropping system, planting date, and environ-ment. Traditionally, we have used a survival rate of 90%.

Figure 1. Corn seed survival across years in tradition-al and organic cropping systems. Data are derived from UW Corn Hybrid Performance Trials conducted between 2008 and 2018 (N= 12,036 plots).

Table 1. Corn seed survival in traditional trials across locations and production zones in Wisconsin. Data are derived from UW Corn Hybrid Performance Trials from 2007 to 2018 (N= 12,036 plots).

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More recent data indicates that 90 to 92% is a reasonable survival rate. However, seed survival at some locations and years can be as high as 95% and would need to be taken into account in order to achieve the target plant density.

The Corn Yield Gap In WisconsinDr. Joe Lauer, UW-Madison Agronomy and Extention State Corn Specialist

Corn yields have been increasing in Wisconsin at the rate of 2 bu/A*yr (USDA-NASS) and there is no indication that corn yields are plateauing. The highest recorded state average yield occurred in 2016 at 178 bu/A. In 2012, Jeff Laskowski (Portage county) recorded the highest corn yield in Wisconsin at 327 bu/A. In the Wisconsin NCGA Corn Yield Contest yields above 300 bu/A have been recorded 21 times.

“Yield gaps” are the difference between potential crop yield and actual farmer yield. Potential yield is defined as the yield of a hybrid when grown in environments to which it is adapted; with nutrients and water not limit-ing; and with pests, diseases, weeds, lodging, and other stresses effectively controlled. Previous corn yield gap estimates from around the world have ranged from 11 to 84%. Lower yield gaps are typically seen under irrigated conditions. It is not clear if potential yield is determined by soil type or if eliminating water and nutrient stresses is more important. Political boundaries and technology availability also affect potential yield.

The challenge in understanding a yield gap is determin-ing potential yield. The gap depends upon the method used to estimate yield potential. Some researchers use crop modeling techniques, others use yield maps from precision farming, or various statistical techniques, or yields from ag research station experiments, etc. Regard-less, potential yield is location specific. The larger the geographical scale used to estimate potential yield and farmer yield, the more difficult it is to estimate a yield gap and to identify management practices that reduce or eliminate the yield gap.

The NCGA Corn Yield Contest consists of three catego-ries: rain-fed, irrigated and conservation tillage. Overall winners of the contest over time regardless of category were used to set the potential yield for corn. Although most winners in the NCGA contest are from southern Wisconsin where farmers use longer-season hybrids with

greater yield potential, the overall record and 8 of 21 yields above 300 bu/A are from north central Wisconsin. USDA-NASS average corn yields were used for farmer yields.

The regressions in Figure 1 show farmer and potential yield for Wisconsin. USDA-NASS yield (farmer yield) has increased from 96 bu/A in 1983 to 166 bu/A in 2018. The Wisconsin NCGA winners (potential yield) have increased yield from 184 to 320 bu/A. The yield gap in 1983 was 87 bu/A (47.6%), while the yield gap in 2018 was 155 bu/A (48.3%). The yield gap was widest in 2012 at 207 bu/A (63%) and narrowest in 1997 at 87 bu/A (40%). Clearly corn yields are increasing, however, the yield gap in 2018 is relatively the same as the yield gap in 1983 at about 48%. Surprisingly, the yield gap among NCGA categories is not statistically different (data not shown).

Wisconsin corn production is a highly developed, so-phisticated, high-yielding production system making it unlikely that variation exists in the availability of tech-nology. Many farmers use the best technology available, however, some farmers choose not to employ the same level of technology as yield contest winners. At the farm level, yield gaps in many fields can be reduced by rela-tively simple changes in management practices. Yield maps are one way to identify yield gaps within a field and on your farm.

Figure 1. Corn yield gap between USDA average yield (farmer yield) and winners of the Wisconsin NCGA yield contest (potential yield). Data derived from US-DA-NASS and NCGA corn yield contest winners.

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Video: POST-Emergence Pigweed Control with Contact Herbicides in SoybeansDr. Rodrigo Werle Assistant Professor & Weed Specialist Department of Agronomy

In this demonstration video, Dr. Rodrigo Werle discusses some of the considerations when using contact-based products such as PPO-inhibitors (group 14) and glu-fosinate (group 10) for POST-emergence weed control in soybeans. To be effective, these products should be sprayed to small weeds, preferably under low population density, and with high gallonage (GPA) with recommend-ed adjuvants. Small weed size and good spray coverage are crucial for efficacy of contact herbicides.

https://vimeo.com/326965504