Adjusting fertility programs for lower than expected yields

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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 management:

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.

click image to zoom Nitrogen management:

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 los 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.

Soil Testing

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%20 [verified 17 September 2012]


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