Spatiotemporal Variability Of Soil Nutrients And Driving Factors In Nihegou Watershed In The Last 40 Years

The Nihegou watershed is a typical gully region of the Loess Plateau.It has experienced nearly 20 years of centralized governance and more than 10 years of socialized free management.Vegetation has been restored,soil erosion has been controlled,and land productivity has been greatly improved.However,whether soil nutrient content has been improved correspondingly,we still need to study the change of soil nutrient content on the basis of previous studies.Based on macroscopic investigation,microscopic analysis and watershed information feedback experiment,the evolution and distribution characteristics of soil nutrients in small watershed were studied,and spatiotemporal variability of soil nutrients and its influencing factors were analyzed,and put forward a new strategy for land use management.The main findings are as follows:1.In the past 40 years,the soil nutrients in the river basin showed an upward trend.It is mainly manifested by the increase of soil organic matter,total nitrogen and available phosphorus,and the content of soil total phosphorus has decreased slightly.The changes of soil organic matter and total nitrogen content were relatively close,and all showed an accelerated increase.The total phosphorus content in soil changed very steadily in 1980~2004 years,and decreased slightly in the past 10 years.The soil available phosphorus content increased greatly in 1980~2004 years,and also showed a downward trend in the past 10 years.2.According to the spatial distribution characteristics of soil nutrients,there are great differences in the spatial distribution of soil nutrients in the watershed.In the whole basin level space,the spatial distribution of soil organic matter content is manifested as gully slope higher than ditch bottom,and Dimuzhuang higher than Zhuitou.The available phosphorus is manifested as orchards higher than woodland.On the whole slope surface,the spatial distribution of soil organic matter content is manifested as plateau plain higher than plateau area,gully slope land higher than gully bottom.The contents of water ridge to gully decreased significantly,and the available potassium appeared on the plateau higher than gully.The spatial distribution of available phosphorus content in the whole sloping farmland is the lower part higher than the upper part.3.From the factors affecting the temporal and spatial variability of soil nutrients,the construction of terraced fields and increased chemical fertilizer played an important role in the variability of soil nutrients.The variation of soil organic matter and total nitrogen amount caused by terrace construction accounted for 28.4% and 21.8% of the total variation.The variation of soil organic matter and total nitrogen amount caused by increased fertilizer application accounted for 29.3% and 29.0% of the total variation.It is smaller than other that the variation of soil organic matter and total nitrogen caused by other structural factors accounted for 14.7% and 12.4% of the total variation.The evolution characteristics of soil nutrients reflect the benefits of watershed management and farmers’ investment in land,and the spatial distribution characteristics reflect natural factors and human activities on various nutrients.Although crop yield has been greatly improved at the present stage,there are still many hidden dangers in the future agricultural development,such as the decrease of total phosphorus content,the decrease of organic fertilizer input and the increase of soil alkalinity,and the seasonal movement of rural labor force,which has restricted the development of agriculture in the river basin.Although more chemical fertilizers can improve soil nutrient content more effectively,the absorption of various nutrients by crops is balanced,which makes the difference between different types of soil nutrient content increase.Agricultural development model in Nihegou watershed has changed from predatory development to extensive management,from emphasis on yield to quality,which indicates that the era of high crop yield by chemical fertilizer will pass.To better develop agricultural economy,the first thing is to improve farmers’ enthusiasm for production.Therefore,adjusting the structure of fertilization,developing wasteland in a gully area,implementing land rotation system,realizing intensive management and establishing agricultural information forecasting system will be the focus of agricultural development in the future.