Transformation of soil phosphorus fractions: the role of time and fertilisation

Abstract

Context Organic fertilisation may increase soil phosphorus (P) availability and increase risk of P loss to groundwater. Aims To understand the effect of continuously applying organic fertilisers on formation of P fractions. Methods A field experiment was conducted to investigate the effect of different fertilisation (CF, chemical fertiliser; COF, cow dung compost with chemical fertiliser; POF, pig manure compost with chemical fertiliser) on different soil P fractions for five growing seasons. Key results Compared with CF, the COF and POF treatments had significantly higher total P and available P contents in each season. The COF treatment showed the highest concentration of NaOH-Pi; however, POF showed the highest concentration of HCl-Pi in all seasons. There were significant positive correlations between concentrations of total P (r = 0.863, P = 0.001), available P (r = 0.590, P = 0.006), each P fraction (r = 0.447 to 0.862, P = 0.048 to 0.001) and organic carbon concentration. Concentrations of total P (r = −0.473, P = 0.035), available P (r = −0.589, P = 0.006) and each P fraction (except HCl-Pi) (r = −0.711 to −0.476, P = 0.001 to 0.034) showed significant negative correlations with soil pH. Available P concentration showed the highest correlation with concentrations of residual P (r = 0.665, P = 0.007), HCl-Pi (r = 0.413, P = 0.126) and NaOH-Pi (r = 0.282, P = 0.309) in CF, COF and POF treatments, respectively. Conclusions Continuous application of organic fertiliser can significantly improve P availability through impacting distribution of P fractions. Implications Further studies are needed to establish the release risk of each P fraction in soils.