Effects of straw return and nitrogen fertilizer application on photosynthesis, biomass, yield and economic benefits of kidney bean

Kidney bean is an important edible legume crop characterized by a short growth period, strong stress resistance, and wide adaptability. Straw return combined with rational nitrogen fertilizer application is a crucial agronomic measure for improving kidney bean yield and economic performance. However, quantitative analyses of their combined effects on the photosynthesis, biomass, yield, and economic benefits of kidney bean remain insufficient. This study investigated the effects of two straw return methods and four nitrogen fertilizer rates (0, 45, 90, and 135 kg ha⁻¹) on chlorophyll content, photosynthetic characteristics, agronomic traits, root length, biomass accumulation, yield, and planting profit in a kidney bean cropping system in Inner Mongolia over two growing seasons. The results showed that straw return combined with nitrogen fertilizer significantly improved growth and photosynthetic indicators, as well as increasing yield and profit. At the same nitrogen application rate, straw return showed superior performance compared with no straw return. The promoting effect increased with nitrogen rate within the tested range (0-135 kg ha⁻¹). Among all treatments, straw return with 135 kg N ha⁻¹ achieved the relatively highest yield of 3130.73 kg ha⁻¹, while straw return with 90 kg N ha⁻¹ produced the greatest economic benefit of 6312.05 yuan ha⁻¹, which was 16.77% higher than the control. Considering overall performance, straw return with 90 kg N ha⁻¹ is favorable for balancing yield and economic returns, whereas straw return with 135 kg N ha⁻¹ is appropriate for pursuing higher yield. These findings provide theoretical and practical references for rational straw return and nitrogen management in kidney bean production.