ABSTRACT

Soils with continuous application of fertilizer phosphorus (P) may present high accumulations of P and may be at high risk of P loss. In this study, we investigated the effects of different fertilization strategies on soil P dynamics in three typical cropland soils over broad spatiotemporal scales in China. The soil P speciation (characterized both by Hedley fractionation and ³¹P nuclear magnetic resonance (³¹P NMR)) and soil P sorption characteristics were examined under five fertilization treatments: unfertilized control (CK); chemical nitrogen (N) and potassium (K) (NK); N, P and K (NPK); NPK plus straw (NPKS); and NPK plus manure (NPKM). We found that with an increase of 100 kg ha⁻¹ in the cumulative P budget, the increases in Olsen-P and CaCl₂-P contents ranged in 1.98–7.35 mg kg⁻¹ and 0.46–1.46 mg kg⁻¹, respectively, among the three soils. The recovery rates of P in Hedley fractionation (87–111%) were much higher than those of ³¹P NMR spectroscopy (40–91%). More percentage of organic P was detected in Hedley fractionation than ³¹P-NMR in acidic soil, while more percentage of organic P was detected in ³¹P-NMR than Hedley fractionation in neutral and alkaline soils. Chemical fertilizer combined with manure or straw can decrease the bond strength (k) values compared to chemical fertilizer alone, while change trends in the maximum P sorption capacity (Qm) were dependent on the soil types. Moreover, the degree of P saturation (DPS) was significantly correlated with the cumulative P budget in each site. A change point in the relation between DPS and soil organic carbon (SOC) was found. After the change point, the DPS increased by 0.63–1.06% as the SOC increased by 0.1 g kg⁻¹. Agricultural measures that increased the contents of SOC and available P could increase DPS values effectively, especially manure amendment, which should be carefully considered to reduce P loss risk.