Effect of sowing method and row spacing on soil physicochemical properties of oat/forage pea grassland in alpine regions

Grass-bean mix sowing is one of the most important ways to establish cultivated grassland because it improves the physical and chemical properties of soil and the yield and quality of forage. In this study, the soil physicochemical characteristics of oats (Avena sativa)/forage peas (Pisum sativum) were quantitatively analyzed and comprehensively evaluated under different sowing methods (mixed, intercropping, and single sowing) and sowing row spacing (30, 25, 20, and 15 cm) in the alpine region of the Qinghai–Tibet Plateau to investigate the most suitable pattern for planting oats and forage peas in the study area. The planting patterns of oats and forage peas in the study area were investigated. The results showed that grass intercropped with oat and forage peas displayed reduced soil capacity and increased soil porosity compared with that of monosown grass. The soil organic matter content of intercropped and mixed grasses increased by 14.60%～16.27% and total nitrogen content increased by 10.13%～11.39% compared with oat monoculture; compared with forage pea monoculture, the soil organic matter content of intercropped and mixed grasses increased by 10.42%～12.02% and total nitrogen content increased by 13.73%～15.03%. Soil organic matter, total nitrogen, and fast-acting nutrient contents were higher in oat and forage pea mixed grass than in intercropped grass, and soil organic matter, total nitrogen, and fast-acting nutrient contents increased with increasing sowing row spacing in both mixed and intercropped grass. Comprehensive evaluation of the multi-criteria decision-making (DTOPSIS) model showed that treatment of the study area with mixed oat and forage pea with 30 cm row spacing could significantly improve the soil fertility of grassland and therefore was a suitable planting pattern for oat and forage pea in the study area.