Improving the Key Enzyme Activity, Conversion Intensity, and Nitrogen Supply Capacity of Soil through Optimization of Long-Term Oilseed Flax Rotation Planting Patterns in Dry Areas of the Loess Plateau of China

Abstract

Various crop rotation patterns can result in differences in nutrient consumption and the accumulation of toxic substances in the soil, indirectly impacting the soil environment and its nutrient supply capacity. Implementing optimized crop planting practices is beneficial for maintaining the favorable physical and chemical properties of farmland soil in the arid area of northwestern China. This study aimed to establish a crop rotation pattern to improve key enzyme activities and soil nitrogen conversion efficiency, as well as understand the underlying mechanism for enhancing nitrogen supply capacity. A field experiment was conducted to study the effect of four flax planting patterns, which included 13 crop rotation patterns with different crop frequencies: 100% Flax (Cont F), 50% Flax (I) (WFPF, FPFW, PFWF, FWFP), 50% Flax (II) (FWPF, WPFF, PFFW, FFWP), 25% Flax (WPWF, PWFW, WFWP, FWPW), on the key enzyme activities and the rate of soil nitrogen conversion, as well as the nitrogen supply capacity. Here, F, P, and W represent oilseed flax, potato, and wheat, respectively. The results indicated that the wheat stubble significantly increased the intensity of soil ammonification and denitrification before planting. Additionally, the activity levels of soil nitrate reductase and nitrite reductase under wheat stubble were significantly increased by 66.67% to 104.55%, while soil urease activity significantly decreased by 27.27–133.33% under wheat stubble compared to other stubbles. After harvest, the activities of soil nitrate reductase and nitrite reductase under the wheat stubble decreased significantly, and the intensity of soil ammonification, nitrification, and denitrification reduced significantly by 7.83–27.72%. The WFWP and FWFP treatments led to a significant increase in soil nitrogen fixation intensity under various crop rotations after harvest and significantly increased the levels of inorganic nitrogen in the soil before the planting of the next crop. This study suggests that the long-term rotation planting patterns WFWP and FWFP can significantly enhance the key enzyme activities of soil nitrogen conversion and significantly improve soil nitrogen conversion before crop sowing. This may increase the rate of soil nitrogen transfer and raise the available nitrogen content of the soil. These findings are crucial for reducing soil nitrogen loss and improving soil nitrogen nutrient supply capacity in dry areas of the Loess Plateau of China.