Phosphorus Fractions Affected by Land Use Changes in Soil Profile on the Loess Soil

Abstract

To evaluate the effect of land use changes on phosphorus pools and its accumulation in the soil profile on loess soils. This study applied a modified Hedley fractionation method to investigate soil P pools in 100-cm soil profile after conversion of wheat-maize (W-M) to greenhouse vegetable (GV) or kiwi orchard (kiwi). Land use changes from W-M to GV significantly increased total P stock by 82% at 0–100-cm soil profile. In particular, conversion from W-M to GV greatly increased easily available P at 0–80 cm by 11–291%, moderately available P at 0–60 cm by 83–253%, and non-available P at 0–40 cm depth by 42–214%, respectively. Conversion from W-M to kiwi also markedly raised total P stock by 15% at 0–100-cm soil profile, in which easily available P and moderately available P at 20 cm depth increased by 161% and 130%, and non-available P at 80–100-cm depth rose by 85.6%. Land use change also caused a shift in the distribution of P pools, i.e., percentages of easily available P rose by 10–13% at 0–80 cm under GV and by 10–15% under kiwi at 0–100 cm over the W-M. Correspondingly, ratios of moderately available P also increased by 7–8% at 20–60-cm depths and by 7–10% at 0–100-cm depths. By contrast, proportions of non-available P decreased. Our results indicate a huge amount of P accumulated into the soil profile, and its solubility also increased, especially under GV, which would have significant environmental consequences. Therefore, rational P management for cash crops should arouse the attentions in all sectors of the society.