Characteristics of Soil Available P and K of Farmland in Lanzhou Area

80surface soil(0—20cm)samples of different farmlands from 3counties and 5districts of Lanzhou City were investigated,and pH value,electrical conductivity(EC),available phosphorus and available potassium contents were analyzed according to crop species,intensity of land use and tillage method.The results showed that:(1)Average pH value was 8.59,and pH value in farmland where vegetables were grown tended to be lower than in other soils,but the differences were insignificant.Soil pH value in intensively used farmland was significantly lower than in moderately and slightly used farmland.Greenhouse soil pH value average tended to be lower than in traditional farmland and sand-covered fields,but it is not significantly.(2)There was a high variance in EC in the study area,and the coefficient of variance(Cv)was up to107.31%.Differences of EC between different crop species,intensities of land use and tillage methods were all insignificant.(3)Soil available K showed in low variance,and the mean content and Cvwas 362.65mg/kg and 48.81%,respectively.The differences in available K were insignificant between different crop species,intensities of land use and tillage methods.(4)Mean content of soil available P was 14.07mg/kg.Available P in farmland where vegetables were grown was higher than those in others.Sorted by land use intensity,available P was significantly higher in intensively used land soil than in moderately and slightly used soils.There was more available P in greenhouse soil than in sand-covered soil and traditionally used fields.Theconclusion of this study was that crop species,land use intensity and tillage methods could affect pH value and available P content of farmland soil,and acidification and increase of available P content of soils may be mainly due to intensive management of farmland.