Background Soil erosion causes a serious threat to the soil and water resources on which human beings depend at the global scale, and soil erosion survey and assessment at the global/regional and national scale is an important basis for solving this global resource and environmental issue.
Methods This study introduced the background and basic structure of the Conservation Needs Inventory (CNI), and focuses on the system design, model involved for soil erosion estimation, sampling methods, data composition and publication system of the National Resources Inventory (NRI). The system design, modeling method, sampling design, data composition and publication system of the National Resources Inventory (NRI) were analyzed. In addition, the composition characteristics of the major land use types involved in the U.S. soil erosion survey in the past 35 years were analyzed. Based on the relatively complete land use statistics and soil erosion survey results of the NRI, the soil erosion status and evolution characteristics of different land use types in the different regions were studied.
Results The development of soil erosion survey in the U.S. are in three distinct periods: the initial stage (Pre-NRI), the CNI stage and the NRI stage. The NRI system, which has been used since 1977, is a comprehensive survey of natural resources developed from soil erosion survey based on sampling and statistical analysis. The soil erosion survey in NRI involved three land use types of Cropland, Pastureland, and Conservation Reserve Program (CRP). According to the newest NRI summary report released in 2020, the total area of cropland decreased by 2.7% from 1982 to 2017, Pastureland did not change much, and the overall trend of CRP land increased first and then decreased after its implementation since 1986. From 1982 to 2017, at the national scale, both water and wind erosion in the United States showed a decreasing trend with 39.9% and 44.71% reduction, respectively, with a small increasing trend in water erosion from 2007 to 2017. At the regional scale, both water and wind erosion decreased significantly to stable levels in all six regions, with different degrees of reduction in each region, but the overall pattern remained largely unchanged. For the three land use types involved in erosion, there was a significant and sustained increase in wind erosion rates since 2002 for pastureland and CRP land, based on an overall significant decrease on a 35-year scale.
Conclusions This study may provide reference, insights or lessons for the establishment of soil erosion investigation system at regional and national scales. In addition, the erosion evolution pattern in the United States in the past 35-year may provide a scientific basis for studying the erosion evolution pattern and formulating sustainable soil and water conservation development plans.
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