Residue management changes soil phosphorus availability in a long-term wheat-fallow rotation in the Pacific Northwest

Abstract

Crop residue management strategies have exhibited significant effects on crop growth and soil properties, which in turn may influence soil phosphorus (P) transformation and availability. In this study, the effect of long-term (83-year) crop residue management treatments (straw plus 45 or 90 kg N ha−1; straw burning in fall or spring; straw plus manure) on soil P availability and storage capacity in the surface (0–0.3 m) and subsurface (0.3–0.6 m) were investigated relative to straw incorporated into soil (control) in a wheat-fallow rotation in the Pacific Northwest. Compared to the control, N application significantly decreased soil available P by 37–49%, measured as Olsen-P, due to the higher P removal by the wheat crop. The significant decrease in NaOH-extractable inorganic P (Pi) by 31–42% and Oxalate-extractable Fe by 20–27% suggests N application induced Fe associated-Pi release to supply crop growth. Straw burning had no significant effect on soil P balance but decreased available P by 20–36%, which can be attributed to the transformation of labile Pi and/or moderately labile Pi to stable Pi and P downward transport due to the increased pH of 0.4–0.9 and the loss of organic carbon. Fall burning appeared to have a greater effect on soil properties and P chemistry than spring burning. Manure application significantly increased soil available P by 245% in surface soil in 2014 while resulted in obvious negative soil P storage capacity (− 103 mg P kg−1) and high potential of P downward transport due to long-term positive P surplus together with the increase in soil pH of 1.2.