Abstract:

The objective of farmland soil phosphorus (P) management is to meet the P needs of crop growth while reducing the risk of soil P runoff loss. Therefore, it is essential to look for the conditioner agent which can reduce the water-soluble P in the P-rich soils and has little effect on the available P. In this study, calcium chloride, gypsum, limestone powder, ferrous sulfate and aluminium sulfate containing calcium, iron and aluminium were selected as conditioning agents, the effects of the five kinds of conditioner agents on the forms of P in three kinds of vegetable soils (calcareous, neutral and acidic soils) with different pH were studied by laboratory simulation experiment. The results showed that the forms of P in the three soils could be changed by applying the conditioner agents. Calcium chloride, gypsum and limestone powder could promote the transformation of Ca₂-P, Al-P, Fe-P to Ca₈-p and Ca₁₀-P, while ferrous sulfate and aluminium sulfate could promote the transformation of Ca₂-P, Ca₈-P and Ca₁₀-P into Al-P and Fe-P. The reduction of Ca₂-P was most obvious when applied with ferrous sulfate or aluminium sulfate, followed by application of limestone powder. The pH value of calcareous and neutral soils could be obviously reduced by applying calcium chloride or gypsum, and the pH value of the soils increased by applying limestone powder, while application of ferrous sulfate or aluminum sulfate significantly reduced pH of the soils. Both available P and water-soluble P in the soils were decreased by adding each of the five different conditioner agents, and the reduction effect of water-soluble P was greater than that of bio-available P. The most obvious reduction of soil water-soluble P was found at application of ferrous sulfate or aluminum sulfate. Based on the objectives of soil P management and the change of soil pH value after application of the agents, it was recommended that the suitable conditioner agents for reducing water-soluble P in calcareous phosphorus-rich soil was aluminum sulfate or calcium chloride, while aluminum sulfate, calcium chloride or limestone powder were suitable for reducing water-soluble P in neutral P-rich soil, and limestone powder, calcium chloride and gypsum were suitable for reducing water-soluble P in acid P-rich soil.

Key words: P-rich soil, conditioner agent, soil P stability, P forms, available P, water-soluble P