Soil phosphorus after 25 years of cropping with five rates of phosphorus application

Abstract

Rate of change of levels of various soil P forms as affected by P fertilizer application and crop removal is important for determining long term P fertilization policy. A rotation‐fertility experiment conducted for 25 years at the Purdue Agronomy Farm, West Lafayette, IN has provided data for calculating changes in soil P levels. Average annual P applications ranged from 0 to 54 kg/ha. Soil samples taken initially and after 25 years were analyzed for resin exchangeable P, Bray Pl, and total P. A linear relation between P applied minus P removed by cropping and Bray Pl indicated that Bray Pl increased one μg/g for every 17 kg net P/ha added. When P application on some plots was stopped for up to eight years, resin and Bray Pl levels decreased. The rate of decrease was greater the higher the P level at the time P application ceased. Increase in soil P level by fertilizer addition and decrease in P level by cropping appeared to be reversible processes.