Red soil is an important soil type that covers a large area, experiences excellent climate conditions and has great potential for exploitation. It is an important production base for grain, oil, cotton and fruit. Long-term significant leaching and weathering has resulted in low natural fertility of red soils. Long-term unsustainable exploitation has accelerated the process of impoverishment of soil fertility and nutrient loss. Scientific and rational use of the land, and associated improvements in soil structure and increased soil fertility, would be conducive to the sustainable development of farmland ecosystems, to better reflect the value of these farmland ecosystems. Studying the effects of cropping patterns on soil fertility improvements in upland red soil could provide a theoretical basis for recommendations or guidelines for sustainable and efficient cropping systems.
A field experiment was conducted at Jiangxi Agricultural University to compare the effects of different cropping patterns on soil fertility, including soil physical and chemical properties, abundance of soil microorganisms and soil enzyme activities. The experiment consisted of four treatments each with four replicates. The treatments were (A) wheat/soybeans-sesame, (B) mixed green manure-soybean corn-green beans sesame, (C) ryegrass-peanut corn-millet buckwheat and (D) rapeseed-mung bean sweet potato. The results showed that multiple cropping patterns, especially planting green manure and returning green manure, could significantly improve soil fertility. Among the experimental treatments, the biggest improvement in soil fertility was observed for treatment C (ryegrass-peanut corn-millet buckwheat), followed by treatment B (mixed green manure-soybean corn-green beans sesame). Treatment C had the highest values for soil cation exchange capacity, organic matter, alkaline hydrolytic nitrogen, total phosphorus, soil enzyme activities and abundance of microorganisms. Treatment B reduced soil bulk density and increased soil porosity, which consequently improved soil aeration and water permeability. Soil pH value, total nitrogen content, available phosphorus, total potassium and available potassium were all increased for Treatment B. Compared with the previous planting, various multiple cropping patterns led to improved soil fertility. Total nitrogen content declined for all treatments, organic matter and total phosphorus content of treatments A and B also declined, but other indicators improved to some extent. For total nitrogen, although treatments A and B had a spring soybean planting, they showed significant biological nitrogen fixation. If nitrogen input from fertilization, legumes and nitrogen fixation is not taken into account, significant nitrogen losses can still occur. Therefore, if there are legumes in the cropping mix in a mixed cropping system, it is important to pay attention to the total input of nitrogen to maintain the nitrogen balance in the farmland ecosystem. Vigorous promotion of the use of green manure in winter is an effective measure to promote farming ecosystem sustainability in upland red soils.