Adjusting fertility programs for lower than expected yields
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.
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.