不同土地利用类型下氮、磷在土壤剖面中的分布特征

在北京市东南郊大兴区采取了44处0～20cm,20～40cm,40～60cm,60～80cm,80～100cm5个不同深度的土壤剖面样品。按土地利用类型,采样点可分为农田、菜地、果园、林地、草地。土壤剖面中,由表层向深层,pH值升高,有机质、速效磷、全磷、硝态氮、全氮降低,且在20～40cm处有较大变化。表层土壤受土地利用影响,不同土地利用类型的土壤性质差别较大,尤以菜地土壤,pH为8.01低于其他类型土壤的平均值8.27,有机质、速效磷、全磷、硝态氮、全氮都高于其他类型的土壤,分别是其他类型土壤的110%～198%,355%～1629%,162%～224%,724%～1540%,130%～248%,速效磷和硝态氮远高于其他土壤。深层土壤性质差异不大,各项土壤性质差异随深度而变小,但菜地80～100cm处,硝态氮含量为18.8mgkg-1,是同深度其他类型土壤的175%～389%。土壤中硝态氮的积累情况,菜地>农田、果园、林地>草地。磷的积累与氮不同,速效磷在0～20cm大量积累,不同类型的土壤,速效磷积累差异显著,在40～60cm处,菜地速效磷含量是其他利用类型土壤的161%～602%;在80～100cm处,不同利用类型的土壤中速效磷无显著性差异。这一情况表明,菜地的过量施用氮、磷肥导致了土壤中的磷和氮大量积累,并以速效磷、硝态氮的形态向下淋溶并在深层土壤中积累。硝态氮在80～100cm的积累仍相当严重,有继续向下淋溶的可能,速效磷的淋溶在80～100cm处已较为微弱,其淋溶过程主要在0～60cm处。对速效磷和硝态氮的累积进行多元线性回归分析,发现速效磷与全磷含量有着良好的线性相关性,而与有机质和全氮含量关系不大。硝态氮则受土壤中pH、有机质和全氮3因素的共同影响。

Distribution characteristics of nitrogen and phosphorus in agricultural soil profiles under different landuse

Soil samples in the profile of 0-20 cm,20-40 cm,40-60 cm,60-80 cm and 80-100 cm were collected from forty-four sites in Daxin district,Beijing.Landuse of these sampling sites can be identified as farmland,vegetable land,orchard,grass land and forest.Along the soil depth,soil organic matter(OM),Olsen P,total P,NO3-N and total N decreased and the soil pH increased with the most obvious changes observed at the depth of 20-40 cm.Landuse pattern,especially vegetable growth,significantly affected the surface soil properties.The SOM,Olsen-P,total P,NO3-N and total N were much higher in the surface soils(0-20 cm)from vegetable land than in the other soils.The soil pH for vegetable land was 8.27 compared to the value of 8.01 for the other soils.The difference in soil properties in the deep layer was less affected by the landuse pattern.The content of NO3-N in the soil profile followed the order:vegetable land > farmland,orchard,forest> grass land.Even in the depth of 80-100 cm,the NO3-N of vegetable land was 18.8 mg kg-1,as much as 175%-389% the other landuse soils in this layer.The distribution of P in the soil profile was different from that of N.The olsen P was mainly accumulated in the soil of 0-20 cm layer.Significant differences in olsen P were observed among the landuses..In the 40-60 cm layer,the Olsen-P in vegetable land soils was as much as 161%-602% the other landuse soil.Such differences were not obvious in the 80-100 cm depth This study indictes that exceeding fertilizer application leads to the accumulation of N and P in the vegetable land soil.They were transported as the forms of NO3-N and Olsen-P to the deeper layers of the soils.Multiple regression analysis showed a linear correlation between the Olsen-P and the total P in different soil profiles.However,no significant correlation existed between the soil OM and total P.The content of NO3-N had linear correlation with the pH,OM and total N.