Nutrient Applications Reported by Farmers Compared with Performance-Based Nutrient Management Plans

Abstract

This study had two main objectives: (i) to evaluate how well farmers implemented nutrient management plans (NMPs) by comparing the farmers' reported practices with the recommended management for manure and fertilizer; and (ii) to evaluate whether the management of manure and fertilizer had significant effects on the nutrient status of soil and corn tissue tests. The analysis relied on data from four dairy farms that had 5 to 7 yr of records at the field level. The farmers chose to apply the recommended amount of fertilizer P from 50 to 100% of the fields. The amount applied was often only 10 to 20 kg P2O5 ha(-1) different from the recommended amount. The farmers applied the recommended amount of fertilizer N from 40 to 71% of the fields when the pre-sidedress soil nitrate test (PSNT) was used for the recommendation, but only 1 to 21% of the fields received the recommended amount when the yield goal method was used. These data suggest that the farmers trusted a fertilizer recommendation developed from a soil test more than they trusted a nonsoil test recommendation. Only a small percentage of fields (3-37%) received the recommended amount of manure N and P. Variability in the amount of residual N available from previous manure applications caused great variation in the PSNT and corn stalk nitrate values (CSNT). This variation in N availability in fields indicates that a number of years of data are needed before the PSNT and the CSNT can be used to objectively evaluate the performance of an NMP.