LONG-TERM CROP-ROTATION AND FERTILIZER EFFECTS ON PHOSPHORUS TRANSFORMATIONS .2. IN A LUVISOLIC SOIL

The effects of different cropping systems. fertilizer. and lime on soil phosphorus (P) dynamics in soils developed under forest vegetation have received little attention. The objective of this study was to develop an understanding of P fractions and transformations in long-term rotation plots on a Luvisolic soil at Breton. Alberta. Results have shown that crop rotation and fertilizer application have affected more inorganic soil phosphorus (Pi) and organic phosphorus (Po) fractions. as determined by a sequential extraction procedure. Continuously cropped treatments. which had not received fertilizer, resulted in P drawdown of resin-extractable Pi (resin-Pi). sodium bicarbonate-extractable Pi (bicarb-Pi), sodium hydroxide-extractable Pi (NaOH-Pi). sodium bicarbonate-extractable Po (bicarb-Po), sodium hydroxide-extractable Po (NaOH-Po) and hydrochloric acid-extractable Pi (HCl-Pi) fractions. Only the residual-P fraction (insoluble Pi and stable Po forms) was unaffected. Addition of fertilizer had an effect on all P fractions except the NaOH-Po fraction. Phosphorus fertilizer treatments positively affected the Pi fractions and N fertilizer positively affected the bicarb-Po fraction. Lime application affected soil pH, which lowered NaOH-Pi levels and increased HCl-Pi levels through formation of more stable calcium phosphate compounds. Addition of lime also resulted in lower bicarb-Po levels. Cropping without using phosphate fertilizer has resulted in a 30-40% decline in total-P in the Breton plots in the Ap horizon. Continuous cropping. with a forage crop in the rotation. coupled with modest N and P fertilizer application. had the most positive effects on P cycling and transformations. Summerfallow had no apparent beneficial effects on P transformations.