Integrated biochar and green manure improve maize productivity and soil health under reduced nitrogen fertilization in yellow soil

Introduction: Excessive nitrogen use threatens the environmental sustainability and soil health. Application of biochar or green manure is a promising strategy to improve the soil health and plant productivity. However, the effects of their combined application in yellow soils remain underexplored. Methods: A two-year field study was conducted to investigate the combined effects of biochar and green manure on maize productivity and soil health. The experimental treatments were comprised of zero fertilizer (control), 100% nitrogen fertilizer, 100% nitrogen with biochar, 100% nitrogen with green manure, 100% nitrogen with biochar and green manure, and 80% nitrogen with biochar and green manure. Maize yield and soil properties were measured. Results: Results showed that plant yield, soil nutrient content, carbon fractions, and enzyme activities were significantly high at 100% nitrogen with biochar and green manure application, compared with control. Furthermore, application of 100% nitrogen with biochar and green manure achieved the highest water-stable macro-aggregates (WS-MA), the smallest percentage of aggregate destruction (PAD), and the optimal maize yield. However, maximum nitrogen-use efficiency was observed at 20% reduced nitrogen with biochar and green manure application. Soil carbon components were significantly positively correlated with water-stable aggregates and enzyme activities, and the soil quality index (SQI) was linearly positively correlated with ecosystem multifunctionality (EMF). Conclusions: Combined application of biochar and green manure significantly improves soil fertility in yellow soils by enhancing nutrient availability, aggregate stability, carbon fractions, and soil enzyme activities. Notably crop yield and quality were maintained even with a 20% reduction in nitrogen fertilizer. These findings highlight the effectiveness of integrating biochar and green manure as a sustainable fertilization strategy that enhances soil health while reducing chemical nitrogen inputs.