When should wheat phosphorus recommendations be based on build-maintenance rather than sufficiency? An economic analysis

Abstract

This article presents an economic analysis of two phosphorus (P) fertilizer recommendation approaches, sufficiency and build-maintenance, in the context of Kansas and Oklahoma wheat (Triticum aestivum L.). Sufficiency seeks to meet crop needs rather than build soil fertility. Build-maintenance, however, builds P levels to a target level of soil test phosphorus (STP) and then maintains that level by replacing the P removed by the crop. The Oklahoma and Kansas sufficiency approaches recommend less P than their build-maintenance alternatives. The research objective was to determine when one approach is preferred over the other. Through dynamic simulation, the net present value (NPV) of these two alternatives was estimated under alternative scenarios. A meta-analysis of previous experiments supported the assumption that with Mehlich-3 STP levels of 15 mg kg^‒1, yield would be 90% of maximum yield even when the recommended sufficiency levels were applied. The estimate from the meta-analysis was a 9% yield loss, and the null hypothesis of no yield loss was rejected (p < 0.0001). The scenarios considered varied initial STP, yield potential, and prices. Sufficiency had a higher NPV under almost all 4-year planning horizons. With a longer 20-year planning horizon, build-maintenance was always preferred. With an 8-year planning horizon, the preferred system varied depending on assumptions with build-maintenance preferred more often. The finding of build maintenance being more competitive in the long run should hold for other crops and locations using approaches like those in Oklahoma and Kansas.