OSU Extension Darke County
Agriculture Continues to Deal With The Drought Even After Nice Rains
By Sam Custer 

Last week I had the opportunity to complete our fall weed in soybeans survey for Darke County.  The information gathered in this survey is submitted to The Ohio State University and is used to continually attempt to stay a step ahead of the weed population as farmers across our country work to feed our population. 

The survey called for me to evaluate fields in a 100 mile loop around the county, checking a soybean field each mile of the loop.  I found for the most part that most soybeans were free of a heavy weed population.  Marestail appears to be the largest issue for Darke County Farmers.  Forty percent of the 111 field evaluated had at least some invasion of Marestail. 

OSU Extension continues to provide guidance for the industry in fighting Marestail.  You can find specific information at http://agcrops.osu.edu/specialists/weeds/specialist-announcements/marestail%20fact%202011.pdf. 

Did You Know 

Did you know that Darke County leads the state in the number of farmed acres at 351,000 acres, Mercer and Richland Counties follow at a distant at about 295,000 acres?  In 2011 Darke County led the state in corn production and was second in the number of swine. 

Aflatoxin Found in Corn in Some Parts of the State 

Reports of aflatoxin contamination of corn continue to come in from some parts of the state, especially those areas most severely affected by drought conditions. There have also been reports of a few loads of grain being docked at some elevators due to aflatoxin levels above thresholds. Producers in affected areas are encouraged to continue sampling and testing grain for aflatoxin in order to determine whether or not the grain is contaminated and at what level. These are the first and most important steps when making decisions as to what to do with contaminated grain. As of today, I have not heard of any levels of aflatoxin affecting delivery of grain in Darke County. 

Soil Nutrient Management Critical after the Drought 

Yield expectations across Ohio are variable based on summer rainfall patterns, so nutrient management strategies will vary greatly. Several good articles from states across the Midwest have highlighted some considerations for adjusting 2013 fertility programs based on lower than expected yields in 2012 (see references below).  Below are some highlights from these articles and past Ohio experiences to consider. 

Phosphorous and potassium are fairly immobile in soil and predictable in crop utilization. Even with newer hybrids and varieties, removal rates are similar enough that book values can be used to estimate nutrient removal from the harvested portions of crops. Phosphorus and potassium removal rates based on Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat and Alfalfa bulletin E-2567 are shown in Table 1. To estimate phosphorus and potassium removal, yield is multiplied by nutrients removed per unit of yield.  The table below shows nutrients removed per unit area plus spaces to enter crop yield and removal based on actual yield. Unused fertility can be credited to next year’s crop if annual fertilizer applications are made. If two-year fertilizer applications were made, soil test prior to the 2014 crop. 

Nitrogen is an expensive nutrient, and drought-affected areas with lower than anticipated yields may have excess nitrogen in the form of nitrate. Nitrate is subject to lost via leaching (when soils have more incoming water than the soil can hold) and denitrification (when soils are waterlogged). Leaching and dentrification are both less likely to occur under drought conditions.  In a normal growing season, we would not expect nitrate levels to be adequate for the next year’s crop because of loss due to crop removal as well as by denitrification and/or leaching. A fall crop (winter wheat) or cover crop may recover the residual soil nitrogen. However, it is difficult to predict nitrogen uptake of crops and subsequent nitrogen release. 

A presidedress soil nitrate test (PSNT) measures soil nitrate-nitrogen and can be used to predict the likelihood of corn grain yield response to sidedress nitrogen application.  The PSNT is primarily used on soils that had cover crops planted or manure applications. To attain a representative soil sample, collect 15, 1-ft deep random cores from a field and mix them thoroughly. Submit a grab sample from the composite to a reputable lab. If the nitrate-nitrogen level in the soil is between 25-30 ppm then additional nitrogen is probably not warranted. Nitrate-nitrogen levels lower than 25 ppm have an increased likelihood of yield response, but the rates should not be greater than 70 lbs N/A (assuming N was applied prior to or at planting). Work out of Illinois reveals that application of only 50 lbs N/A results in maximum yield over a wide variety of growing conditions. 

If you use soil test results to track trends on your farm, which is a good practice to monitor fertility programs, you may note some soil test results this fall that do not follow trend. Dry soils can affect soil chemistry, soil structure, short-term nutrient cycling and ultimately soil test results. Wait until more normal soil moisture conditions before taking a soil sample. Make sure the soil probe can get into the ground to your standard soil sampling depth of 6-8 inches. Factors which may be affected by dry soil are: 

pH- Water pH maybe 0.1-0.3 units more acidic but differences in buffer pH used to calculate lime recommendations are not large or consistent so lime recommendations will not be different under dry conditions. 

P&K- Soil K levels are influenced by dry soil. Soils with low K may show an increase in soil test K while soils with high K may show a decrease in soil test K. Soil P test results probably will be affected little by dry soil conditions.      

References: 

Phosphorus, Potassium and pH Management Issues Following Drought-damaged Crops. Mallarino, A.  and Sawyer, J. http://www.extension.iastate.edu/CropNews/2012/0823mallarinosawyer.htm [verified 13 September 2012.] 

Cover Crops Following the Summer 2012 Drought. Kladivko, E. https://ag.purdue.edu/agry/extension/Documents/CoverCropsFollowingDrought.pdf [verified 13 September 2012] 

The presidedress soil nitrate test for improving N management in corn. Sylvie M. Brouder and D.B. Mengel https://www.agry.purdue.edu/ext/pubs/AY-314-W.pdf  [verified 13 September 2012] 

Nutrient Management Related to Dry Soil Conditions and Poor Crop Yields.  Jim Camberato and Brad Joern.  http://www.agry.purdue.edu/ext/soilfertility/droughtnutrients.pdf [verified 17 September 2012] 

For more information visit our web site at http://darke.osu.edu/  or contact Sam Custer at 937.548.5215.