Effects of improving soil fertility by planting different leguminous green manure plants under different mixed cropping patterns

Field experiments were conducted in Zhaosu, Xinjiang, from 2017 to 2018 to illuminate the influence of green legume manure plants peanuts, chickpeas, and white sweet clover on soil nutrient concentrations and the aboveground biomass of selected intercropped/rotated crops corn, oilseed rape, barley, and oat. The improvement of soil nutrients was compared under different planting patterns by measuring changes in soil organic matter, nitrogen, phosphorus, and potassium concentration, aboveground biomass, and land equivalent ratios. The results showed that: (1) Compared with a crop monoculture, the green legume manure plants intercropped with corn, mixed oilseed rape, barley, and oat rotations had improved soil organic matter, total nitrogen, and alkali hydrolyzed nitrogen of the soil surface. However, the planting patterns had little effect on total potassium concentration in the soil surface. Furthermore, the sweet clover + barley and oats rotations improved the total phosphorus and available phosphorus concentration of the soil surface. The spatial structure of intercropped and mixed patterns also affected improvements in soil nutrient concentrations. (2) Compared with the soil nutrient concentration before the field experiment, soil organic matter, total nitrogen, total phosphorus, total potassium, alkali-hydrolyzed nitrogen, and available phosphorus increased by 40.43%, 50.00%, 10.00%, 27.93%, 76.75%, and 45.13%, respectively, under the white sweet clover + barley rotation. (3) The aboveground biomass of maize, oilseed rape, and white sweet clover for mixed cropping treatments increased by 23.16%, 16.67%, and 27.30%, respectively, when compared with a monoculture. There was a quadratic polynomial function between the increment of aboveground biomass and soil nutrient concentration. Therefore, green legume manures + grass rotations and mulches in the soil, and peanut and corn intercropping improved soil quality by increasing the soil nutrient concentrations of farmlands in Wuerhe area. The planting patterns also produced a crop yield that can provide economic returns. The improvement of soil quality will help to improve the sustainable development of agriculture in this area.