Enhancement of Soil Structure in Sloping Cropland of Karst Areas through "Preferential Entrainment" of Contour Reverse-slope Terrace
Description
Soil aggregates (including large aggregates (>2 mm), medium aggregates (2–0.25 mm), and microaggregates (<0.25 mm)) enhance soil fertility by regulating soil structure and conserving carbon and nitrogen, and affect the ecological construction effect, especially in fragile karst areas with weak soils, high risk of erosion, and high demand for agro-mechanical technologies. This study revealed the significant effects of different ecological construction measures (contour reverse-slope terrace (implemented for 1 year on the basis of sloping cropland), natural vegetation restoration (implemented for 6 years), plantation forest (planted for 7 years), and meridian forest (planted for 6 years) on the content and stability of soil agglomerates, and the changes of carbon and nitrogen contents within the aggregates in the karst landscape, compared with the traditional sloping cropland (38 years of continuous cropping) as a control. The results showed that macroaggregates play a key role in promoting soil structural stability and ecological functions, while microaggregates are the main contributors to soil carbon and nitrogen pools. The contour reverse-slope terrace significantly promoted the formation of medium aggregates and microaggregates, and enhanced the spatial heterogeneity of organic carbon and total nitrogen through the mechanism of “preferential entrainment”, which increased the content of medium aggregates by 34.76%, and the geometric mean diameter and weight by 27.21% and 18.11%, respectively, comparing with sloping cultivated land in the 38–year period. The SOC contribution of large and medium agglomerates increased by 3.21% and 8.55%, respectively, and the total nitrogen contribution of medium agglomerates increased by 12.95%. The natural vegetation restoration measures have the best contribution to carbon and nitrogen pools among all ecological measures, highlighting their advantages in improving ecosystem functions in fragile karst areas. These findings contribute to the understanding of the effects of ecological construction in the southwestern karst region.