Effect Of Long-term Fertilization On Soil Phosphorus Accumulation And Degree Of Phosphorus Saturation In Manural Loessial Soil

In order to provide references for reasonable fertilization and reducing the risk of phosphorus leaching,we investigated the effect of long-term fertilization on soil phosphorus accumulation,leaching and degree of phosphorus saturation in manural loessial soil based on rain-fed and irrigated experiments in Guanzhong Plain,Shaanxi province,China.Both long-term experiments included four treatments,i.e.control(CK,no nutrient input),P and K combined(PK),N,P and K combined(NPK),organic manure(M)combined with NPK(MNPK).Following main results and conclusions have been obtained:1)The total-P,Olsen-P,Mehlich 3-P concentrations of topsoil in different treatments under winter wheat-summer fallow cropping systems showed a decreasing order as MNPK>PK>NPK>CK.Soil Olsen-P in the PK and NPK treatments leached down to a depth of 180 cm compared with CK,while it was 300 cm in the MNPK treatment.Soil Mehlich 3-P in the MNPK treatment also accumulated at 300 cm soil layer compared with CK.2)The total-P,Olsen-P,Mehlich 3-P concentrations of topsoil in different treatments under winter wheat-summer maize cropping systems showed a decreasing order as MNPK>PK>NPK>CK.Soil Olsen-P concentrations in the PK,NPK and MNPK treatments were significantly higher compared with CK below 200 cm soil layer.The accumulation of soil Mehlich 3-P increased significantly in the PK treatment compared with CK.3)Soil Olsen-P and Mehlich 3-P concentrations in the PK treatment were higher under irrigated condition than under rain-fed condition.There was no significant difference in Olsen P between rain-fed and irrigated condition in the NPK treatment.Soil Olsen-P and Mehlich 3-P concentrations of topsoil in the MNPK treatment were significantly higher under irrigated condition than under rain-fed condition,but it was true in deep soil layers.4)Soil CaC12-P and degree of phosphorus saturation(DPS)in the P fertilized treatments showed increasing trends with the increase of fertilization years at both rain-fed and irrigated conditions.Soil CaC12-P and DPS were significantly higher in the MNPK treatment than in the CK,PK,NPK treatments.Soil CaC12-P and DPS in the MNPK treatments were markedly higher under irrigated condition than under rain-fed condition.while soil CaC12-P and DPS in the PK and NPK treatments were markedly higher in rain-fed condition than in irrigated condition.5)Soil DPS showed positively and significantly correlation with soil organic carbon,Olsen-P and CaCl2-P,which implies less soil P adsorption and increasing risk of soil phosphorus leaching.In summary,soil phosphorus accumulation was observed at deeper soil layer and even below 300 cm soil layer in the PK treatment at both rain-fed and irrigated conditions,in such case soil phosphorus leaching was more likely in irrigated condition than that in rain-fed condition.Soil available phosphorus accumulation occurred in below 100 cm under long-term balanced fertilization.Soil available phosphorus accumulation occurred in the deep soil and even below 300 cm by long-term organic and inorganic fertilizer application,which was more serious in rain-fed soil than in irrigated soil.Soil phosphorus leaching was related to the significant increase of soil DPS by long-term Pover fertilization.