Effects Of Forestland Reclamation And Erosion On Spatial And Temporal Distribution Of Soil Nutrients Along Slopes In Loess Hilly Region

Forestland reclamation and the subsequent soil erosion process will lead to serious soil degradation and resulting in the loss of soil nutrient,but the impact of forestland reclamation and erosion on the spatial and temporal distribution characteristics of soil nutrients on slopes and their relationship are not yet clear,limits the understanding of erosion slope soil degradation mechanism.In this study,soils were collected in the Ziwuling forestland and different types of erosion slopes after 28 years of forestland reclamation,in the hilly area of the Loess Plateau.The effects of forestland reclamation,slope scale and upper sediment runoff on soil properties and nutrients distribution were analyzed.The research conclusions are as follows:(1)After the forestland reclamation,the contents of soil organic matter,total nitrogen,total phosphorus,ammonium nitrogen,nitrate nitrogen,available phosphorus and available potassium decreased while the p H value increasing.Soil quality decreased significantly.Nutrient contents decreased less in the upper of the slopes and more in the middle and lower of the slopes.(2)In the vertical direction(0-10,10-20,20-40 and 40-60 cm),the contents of soil organic matter,total nitrogen,total phosphorus,nitrate nitrogen,ammonium nitrogen,available phosphorus and available potassium decreased continuously along the depth of the soil layer,and the soil nutrients were mainly enriched in the surface layer(0-10 cm).However,the decrease of deeper soil nutrients in the sedimentary area is lower than that in the erosion area,where nutrients gradually migrate to the deep layer.(3)After a rainy season,the contents of soil p H,organic matter,total nitrogen,ammonium nitrogen,nitrate nitrogen and available potassium decreased to different degrees on different slopes.Among them,the nutrient decreased most in the erosional area with a large slope,while the nutrient content increased in the erosional area at the bottom of the slope.However,the phosphorus content was higher than that before the rainy season.(4)The soil nutrients decreased with the increase of slope length,but not with the increase of slope width.The soil nutrients content was the highest when the slope width was 5 m.The longer and wider slope,content of soil organic matter,total nitrogen and total phosphorus were higher,and content of ammonium nitrogen,nitrate nitrogen,available phosphorus and available potassium were lower,erosion gradually becomes the dominant factor of nutrient profile distribution on the slope.After the rainy season,the variation trend of nutrient content with slope length and slope width before and after rainy season was inconsistent.(5)The soil nutrients on the slope are easily brought out of the slope by up-slope runoff and sediment,which leads to the nutrient cannot be enriched at the bottom of the slope and migrate to the deeper layer,which affects the profile distribution of nutrients on the slope and reduces the soil quality on the slope.Sediment from above increased the p H value of slope soil more after the downslope rainy season,the loss of organic matter,total nitrogen and available potassium increased,and the loss of ammonium nitrogen,nitrate nitrogen and available phosphorus decreased.