Optimal planting density combined with phosphorus input promotes common buckwheat resource use efficiency and productivity to increase grain yield

A field experiment was conducted on the Loess Plateau in 2021 and 2022, with three planting densities (600,000 plants/ha, 900,000 plants/ha, and 1200,000 plants/ha) and four phosphorus (P) levels (0 kg/ha, 15 kg/ha, 75 kg/ha and 135 kg/ha) designed to study the effects of planting density and phosphate fertilizer management on the growth and resource utilization of common buckwheat. Results showed that optimizing P application (75 kg/ha) and planting density (900,000 plants/ha) effectively improved the resource use efficiency and yield of common buckwheat, as a result of significantly improving photosynthetic capacity and dry matter accumulation. The ability of the buckwheat population to absorb soil moisture and nutrients, as well as intercept IPAR, was maximized through the modification of planting density, thereby further promoting photosynthesis and productivity. The integration of combining moderate planting density with P fertilizer increased yield by boosting buckwheat growth and enhancing resource use efficiency based on the optimization of crop productivity without additional P input. In conclusion, future agriculture should focus on the SPAD value, 1000-grain weight, and illuminance of buckwheat population to effectively increase grain yield. This cultivation system of combining planting density and P application would be a promising alternative agricultural practice. Implementing a planting density of 900,000 plants/ha and a P application rate of 75 kg/ha provide opportunities to improve productivity and sustainability on the Loess Plateau in agriculture.