Phosphorous distribution of plant-soil system in a stipa bungeana slope land in the agro-pastoral transitional zone

Understanding the phosphorous distribution of plantsoil system in a stipa bungeana slope land in the agro-pastoral transitional zone is fundamental for managing phosphorous and predicting phosphorous distribution and loss in slope lands. In this study, the spatial distribution of phosphorous in plant and soil along a stipa bungeana slope in the agro-pastoral transitional zone of the Loess Plateau was analyzed. Three spatial scales were used to analyze the spatial structure of phosphorous along slopes. The results show that the plant biomass, phosphorous content and amount in plant and soils are increased with the decreases of slope position and the variation coefficients of these variables are smaller in the low position than those in the middle and up position. The variation coefficients of phosphorous concentrations in plants and the total phosphorous in soils from the up position to the low position are 34.25%, 25.98%, 10.02% and 24.05%, 15.27%, 10.85%, respectively. The exponential model is the best fit model for plant biomass and soil available phosphorous, spherical model for soil total phosphorous, and Gaussian model for plant phosphorous, respectively. With the enlargement of the analysis scale, the values of C0 and C0/(C0+C) are increased, showing a decreased spatial dependence of sampling sites and weak spatial correlations. The C0 and C0/(C0+C) of phosphorous concentration in plants are 0.010, 0.010, 0.011, and 7.9, 8.5, 8.9, respectively, at the analytical scales of 5, 10, and 15 m. These results indicate that phosphorous in plant and soil has relatively stable spatial structure at different spatial scales which belongs to medium or strong spatial correlations, and its spatial variation mainly comes from structural factors.