Effects of Planting Patterns on Soil Aggregates and Enzyme Activities in Rocky Desertification Areas of Karst Plateau Mountains

Abstract

Soil aggregate characteristics and enzyme activities are key to the sustainable development of soil quality management. However, there are presently few studies on soil aggregate nutrients, enzyme activities, and their driving factors in areas with karst rocky desertification. As such, this study investigated the effects of planting patterns on soil aggregate nutrients and soil enzyme activities under six typical planting patterns (walnut, Rosa roxburghii Tratt, ryegrass, walnut-Rosa roxburghii Tratt, Rosa roxburghii Tratt-ryegrass and walnut-ryegrass) in the karst rocky desertification area of plateau mountains. The results indicated that: (1) there were significant differences in soil aggregate nutrients and soil enzyme activities among the different plots, when compared to traditional farmland, the increase in the aggregate nutrient content and soil enzyme activities was most noticeable in walnut-Rosa roxburghii Tratt, Rosa roxburghii Tratt-ryegrass, and walnut-ryegrass, and the nutrients gradually increased as the aggregate particle size decreased. The maximum C:N and C:P ratios were measured in the 0.25-2 mm aggregates, while the maximum N:P ratios was measured occurred in the <0.053 mm aggregates. (2) The stoichiometric ratios had different degrees of relevance associated with the aggregate nutrients, TN and C:N, SOC and C:P, and TP and N:P showed extremely significant linear correlations. Moreover, a significant correlation also occurred between enzyme activity and aggregate nutrients, particularly in macroaggregates. (3) Soil physicochemical properties, such as the soil total porosity, capillary water holding capacity, saturated hydraulic conductivity, bulk density and pH, had a direct influence on enzyme activity, therefore, the soil condition can be improved by changing the planting patterns to promote enzyme activity. These findings are helpful for the optimal allocation of forest and grass for the comprehensive control of karst rocky desertification.