| In order to systematically expound the influence of shelterbelt on soil nutrient erosion deposition law and availability on slope.the slope with farmland shelterbelt and without shelterbelt were selected as site conditions were basically the same.In each test site,a sample line with a vertical contour line of 390 m and a horizontal distance of 390 m was set up,and 12 sample squares were set at equal intervals on each sample line according to the vertical contour line and the horizontal distance of 30 m.To determine soil organic carbon(SOC),total nitrogen(TN),total phosphorus(TP),alkali-hydro nitrogen,and rapidly-available phosphorus,soil samples were collected from surface layer(0<d≤20 cm)and lower layer(20 cm<d≤40 cm)according to different soil depth(d)in each sample squares.The purpose of this study is to explore the effect of shelterbelt on soil nutrient erosion-deposition laws of slope land in black soil.On this basis,the area with the most obvious nutrient erosion and deposition was selected as the sampling area,corresponding to the sampling area of shelterbelt slope.The parameters of phosphorus adsorption and desorption and the contents of different forms of phosphorus were determined,calculated and analyzed to explore the impact of shelterbelt on slope erosion The adsorption desorption characteristics of soil phosphorus and the effect of phosphorus availability were studied.The main conclusions are as follows:(1)The effect of shelterbelt on the distribution of TP and alkali-hydro nitrogen is caused by directly eliminating the erosion area of organic carbon,total nitrogen and rapidly-available phosphorus in the middle and upper part of slope,blocking the eroded area of organic carbon and total nitrogen in the middle and lower part of slope,reducing the scope of eroded area and realizing the transformation from eroded area to deposition area.In view of the influence of shelterbelts on the spatial pattern of soil nutrient erosion and deposition,it is suggested that the spacing of farmland shelterbelt should be adjusted to 120～140 m in typical black soil area.(2)The isotherm adsorption curve of typical black soil slope soil showed that the phosphorus adsorption capacity increased with the increase of phosphorus concentration in equilibrium solution.The results of Langmuir equation showed that the adsorption characteristics of soil phosphorus in different slope areas had high reliability,and the correlation coefficient was 0.86～0.98.Within the surface soil,the maximum adsorption capacity(Qmax)and maximum buffering capacity(MBC)of phosphorus in the slope erosion area and deposition area were significantly reduced by the shelterbelt.The maximum buffering capacity of phosphorus was reduced by 30.03%and 14.95%respectively,and the maximum buffering capacity of phosphorus was reduced by 13.84%and 41.88%respectively;The adsorption saturation(DPS)of soil phosphorus showed the opposite change characteristics.The adsorption saturation of soil phosphorus in the erosion area and deposition area of shelterbelt slope was significantly higher than that in the non shelterbelt slope.Shelterbelt could effectively reduce the fixation capacity of soil phosphorus in the erosion area and deposition area of slope surface,and make phosphorus easy to be desorbed into the soil,thus increasing the availability of soil phosphorus.Compared with the slope without shelterbelt,the average desorption rate of soil phosphorus in the erosion area and deposition area of the slope with shelterbelt increased significantly,the desorption lag coefficient(HI)showed an opposite trend,and the soil easily desorbed phosphorus(RDP)did not show an obvious rule.It can be considered that shelterbelt can effectively increase the degree of phosphorus desorption and increase the availability of soil phosphorus.The results showed that:compared with the the slope without shelterbelt,the maximum adsorption capacity(Qmax),maximum buffer capacity(MBC)and desorption lag coefficient(HI)of soil phosphorus decreased in the erosion and deposition areas of shelterbelt slope;The adsorption saturation(DPS),average desorption rate and easily desorbed phosphorus of soil all showed an upward trend.It can be considered that the shelterbelt can effectively enhance the phosphorus supply capacity of soil,and then improve the utilization rate of phosphorus.(3)The effect of shelterbelt on soil total phosphorus content in slope erosion area and deposition area was not obvious.Under the action of shelterbelt,The contents of soil available P and inorganic P in the surface erosion area increased significantly(p<0.05),while those in the deposition area decreased slightly;In the subsoil,the shelterbelt can effectively increase the content of soil available phosphorus and inorganic phosphorus in the slope erosion area and deposition area.Phosphorus in slope soil mainly exists in the form of organic phosphorus,and the content of medium active phosphorus is the highest,accounting for 26.01%～35.71%of total phosphorus;The content of H2O-Pi and NaHCO3-Pi,which are most effective to plants,is lower;Soil organic carbon was significantly correlated with total phosphorus,available phosphorus and various phosphorus components,and there was a significant positive correlation between different phosphorus components.It can be considered that the shelterbelt can significantly improve the availability of soil phosphorus in the slope soil erosion area and deposition area,and the most significant effect is on the surface soil in the erosion area.The difference of organic matter content is an important reason for the influence of different phosphorus components in the shelterbelt slope.The results can provide a theoretical basis for the adjustment of shelterbelt spacing and multi-functional control objectives in typical black soil area. |
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