Phosphorus Removal in Corn Grain at Harvest.

The Delaware Nutrient Management Act requires that nutrient management plans be written for most land in Delaware that receives nutrients. This law states that phosphorus (P) cannot be applied at rates greater than three-year crop removal rates. Calculations of crop nutrient removals require knowledge of the concentration of P in the harvested crop and crop yield. Research in the surrounding region has shown wide variation in P concentrations of corn (Zea mays L.) grain, which is a major crop in Delaware. The objective of this project was to determine average nutrient concentrations and ranges in these concentrations in corn grown in Delaware and Maryland. In this project, we analyzed 668 corn grain samples. The results suggest that nutrient concentrations and removals vary considerably for corn among different fields, and that these variations are almost as great within individual fields. This variability suggests little value in analyzing the harvested portion of corn from individual fields but instead using average removal concentrations for writing nutrient management plans. The results also suggest that average P removal concentrations utilized by universities and government agencies around the United States for calculating crop nutrient removals may be too high, with the exception being the Natural Resources and Conservation Service (NRCS) crop nutrient removal database. In other words, most nutrient management plans are probably overestimating P removal concentrations and subsequent P removals for corn grain. The results from this project indicated that the mean nutrient removal concentrations for nitrogen (N), P, and potassium (K) were 0.88, 0.19, and 0.22 kg nutrient per hectoliter of grain, respectively.