Leguminous green manure reduced N inputs and increased yield, quality and N use efficiency of the subsequent tobacco

Inappropriate cultivation patterns and excessive nitrogen (N) inputs in tobacco production has caused lower yield and higher environmental risks. Generally, tobacco rotated with green manure (grown as cover crops) is helpful for reducing N fertilizer inputs while enhancing both yield and quality. However, the influences of different green manures (i.e. leguminous vs gramineous) with optimizing N inputs on the crop-soil interactions remains unclear. This study aims to assess the impacts of four green manures, including white radish, ryegrass, barley and hairy vetch (with fallow as the control) and three N rates on soil chemical properties, N legacy effects, the yield and quality of tobacco using a 7-year experiment and related ¹⁵N tracking test in southwestern China. Our results showed that higher nutrient supplies from leguminous green manures significantly increased available N for the subsequent tobacco growth. Hairy vetch performed best with strongest N legacy effect valued 93.5 kg N ha⁻¹, and the highest tobacco yield of 2320 kg ha⁻¹ among the four manure treatments, which was 66.7 kg N ha⁻¹ and 1176 kg ha⁻¹ higher compared to that in the fallow treatment, respectively. Our results indicate that hairy vetch with N inputs of 67 kg N ha⁻¹ during the tobacco season was the optimal combination in achieving high yield, quality and partial factor productivity of tobacco, which could provide theoretical and technical support for the green development of manure-tobacco rotations in the study region.