Nutrient management related to dry soil conditions
Nutrient Removal in Corn Harvested for Forage
The amount of nutrient removed in drought-stressed corn harvested for forage is difficult to predict. Most estimates of nutrient removal typically used are based on plants with a normal ear, not barren plants. With unusually dry weather nutrient uptake as well as growth has been affected so the nutrient composition of the plants is probably not ‘normal’ either. The best way to determine nutrient removal is to obtain representative samples of the forage and have a commercial laboratory do a nutrient analysis. From the results of the analysis and an estimate of dry matter one can calculate nutrient removal. In the absence of a nutrient analysis a ballpark estimate would be about 0.25% P (0.57% P2O5) and 1.25% K (1.5% K2O). A dry ton of corn forage at these nutrient concentrations contains about 11.5 lb P2O5 and 30 lb K2O. Feed and nitrate analyses should also be requested to determine the value of the forage as a feed resource and any feeding limitations that may arise from high nitrate concentrations. Tamilee Nennich (Dept. of Animal Sciences) developed an information leaflet (see ref. #1) and calculation spreadsheet that can be used to determine nutrient removal and silage value (see ref. #2). Ron Lemenager (Dept. of Animal Sciences) and Keith Johnson (Agronomy) discuss feeding strategies based on feed and nitrate analyses (see ref. #3).
Nutrient Carryover in Poor Yielding Fields
In a dry year loss of nitrogen (N) from the soil via leaching and denitrification are negligible. Removal of N from the field via grain and/or forage harvest can also be greatly reduced with poor yield. Nitrogen accumulated by the crop remaining in the field will be released next season with decomposition of the plant tissues. Much of this year’s N, however, will remain as nitrate-N in the soil. Until rainfall returns to cause tile flow and/or saturated conditions in poorly-drained soils or deep leaching in sandy soils the N fertilizer applied for this season will be retained in the upper soil. Fall small grain or cover crops can scavenge the residual N and utilize it for growth, protecting it from loss. However, dry soil and residual herbicides may make establishment of these crops difficult. The amount of N that can be accumulated by the crops is difficult to predict, but a reasonable range may be 50 to 100 lb N/acre. Deciding how much to reduce next year’s N fertilization rate is also difficult.
Any nitrate-N in the soil this fall, winter, and spring will be subject to loss via leaching and denitrification. If moderate N loss occurs between now and next season, the remaining N can be assessed by measuring the nitrate-N content of a 0-1’- and 1-2’-deep soil sample taken a week or two before corn sidedress. Details on the testing procedure and interpretation of results can be found in ref. #4.
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