The influence of long-term N and P fertilization on soil P forms and cycling in a wheat/fallow cropping system

Efficient phosphorus (P) management is important for crop production and environmental sustainability of cropping systems. The effects of the agricultural management practices of crop rotation and fertilization on soil P forms and cycling were investigated in plots in Swift Current, SK, Canada, under three crop rotation phases [fallow (F), wheat after fallow (WF), and wheat after wheat (WW)], with four nitrogen (N) and/or P fertilizer treatments (+N+P, -N+P, +N-P, and -N-P), using techniques including sequential fractionation, P-31 nuclear magnetic resonance (P-NMR), and P K-edge X-ray absorption near-edge (P-XANES). Soil total P (TP) and organic P (Po) concentrations were significantly reduced in F and WW phases compared to WF regardless of fertilization practice. Compared to WW, WF had the highest grain yield and nutrient uptake. Fertilization with N and P significantly influenced soil total carbon (C), total N, TP, and Mehlich 3-P concentrations and acid phosphatase activities, as well as the concentration of some P pools by sequential fractionation and stable P determined by PXANES. Stopping P fertilization significantly increased the proportions, but not concentrations, of soil P-o determined by P-NMR compared to plots still receiving P fertilizers, while the concentration of total diesters increased in plots fertilized with N. Redundancy analysis showed that soil pH and organic C were the significant predictors of P forms in these soils, suggesting that long-term N and P fertilization altered soil P forms by changing soil chemical properties.