Land Use Changes Impact Distribution of Phosphorus in Deep Soil Profile

Abstract

It is of paramount importance to assess phosphorus (P) accumulation and distribution in deep soil profile after land use changes to improve current P management. This study investigated soil P fractions and degrees of P saturation in 300-cm soil profile after conversion of wheat–maize cropping to greenhouse vegetable or kiwi planting in Yangling, Northwest China. Compared with the arable land, vegetable greenhouse or kiwi orchard showed significantly greater soil P accumulation at surface layer, i.e., CaCl2-P increased by 10–20 times, Olsen-P by 3–5 times, Mehlich-3-extracted P by 3–6 times, and organic-P by maximum of 4 times. A degree of P saturation increased from 4 under arable crop to 14% under kiwi orchard and 22% under greenhouse vegetable. Land conversion also markedly increased soil available P (Olsen-P and Mehlich-3-extracted P) distributing in deep soil layers down to 300 cm, especially for greenhouse vegetable, where Olsen-P or Mehlich-3-extracted P contents reached the critical P value for arable crop to achieve maximum yield. Our results indicate a huge amount of P had been further leached down to deep soils under the current management. Hence, there is an urgent need to update the P management strategies under greenhouse vegetable and kiwi orchard, especially for those involving in amendment of organic manure, to prevent the situation from getting worse in future.