Interaction of NPK Fertilizers During Their Transformation in Soils: Ⅲ. Transformations of Monocalcium Phosphate

Interactions of N, P and K fertilizers in soil-plant systems are widely recognized. This study focused on the transformations of monocalcium phosphate (Ca(H2PO4)2) (MCP) with co-application of ammonium and potassium fertilizers in three different soils. The results showed that after 1 d incubation a large portion of the MCP applied in the paddy,calcareous and red soils became the water-insoluble form and the recoveries of P applied as Olsen P varied greatly in these three soils. Application of ammonium sulfate ((NH4)2SO4) (AS) or potassium chloride (KC1) reduced WSP significantly in the soils with AS more effective than KC1 in the calcareous soil, while the reverse occurred in the red soil. Meanwhile, in the paddy soil, co-application of the two fertilizers reduced WSP more than when the fertilizers were applied individually. The co-application of AS with MCP in the paddy and calcareous soils significantly reduced Olsen P, but the opposite occurred in the red soil. The experiment on the effect of different accompanying anions showed that the ammonium fertilizers (PNC1 and PNS) reduced WSP more effectively than the corresponding potassium fertilizers (PKC1 and PKS) in the calcareous soil due to the difference of the cations, whereas in the red soil, the chlorides reduced WSP more effectively than the sulfates. Overall, co-application of ammonium or potassium fertilizers with MCP significantly decreased availability of P from MCP during its transformation in soils, especially when MCP was applied in combination with ammonium in the calcareous soil.

Interactions of N, P and K fertilizers in soil-plant systems are widelyrecognized. This study focused on the transformations of monocalcium phosphate (Ca(H_2PO_4)_2) (MCP)with co-application of ammonium and potassium fertilizers in three different soils. The resultsshowed that after 1 d incubation a large portion of the MCP applied in the paddy, calcareous and redsoils became the water-insoluble form and the recoveries of P applied as Olsen P varied greatly inthese three soils. Application of ammonium sulfate ((NH_4)_2SO_4) (AS) or potassium chloride (KCl)reduced WSP significantly the soils with AS more effective than KCl in the calcareous soil, whilethe reverse occurred in the red soil. Meanwhile, in the paddy soil, co-application of the twofertilizers reduced WSP more than when the fertilizers were applied individually. The co-applicationof AS with MCP in the paddy and calcareous soils significantly reduced Olsen P, but the oppositeoccurred in the red soil. The experiment on the effect of different accompanying anions showed thatthe ammonium fertilizers (PNCl and PNS) reduced WSP more effectively than the correspondingpotassium fertilizers (PKCl and PKS) in the calcareous soil due to the difference of the cations,whereas in the red soil, the chlorides reduced WSP more effectively than the sulfates. Overall,co-application of ammonium or potassium fertilizers with MCP significantly decreased availability ofP from MCP during its transformation in soils, especially when MCP was applied in combination withammonium in the calcareous soil.