Objectives We studied the variation of yield and soil fertility under different replacing percentages of chemical fertilizer inputs with long-term application of green manure in Hexi oasis irrigation area.

Methods The long-term experiment was carried out in Hexi Oasis Irrigation Area since 1988, the cropping system is spring wheat- summer maize intercroping. The experiment designed four treatments: CK (no fertilization), NP (chemical fertilizer only), GP (green manure) and 1/2GNP (1/2 green manure and 1/2 nitrogen fertilizer) , the green manure is Vicia sativa. The crop yield were recorded every year, and soil samples at the 0−20 cm arable layer were collected in 2022 for measurement of pH, organic matter, and nutrient contents.

Results Compared to NP treatment, the GP and 1/2GNP treatments increased the average wheat yield by 18.08 and 11.58 percentile, respectively. In the first 20 years of the experiment, the yields of maize and the intercropping system showed an order of NP > 1/2GNP > GP. However, the yield gaps of 1/2GNP and GP treatment with that of NP narrowed over time, became statistically insignificant after 35 years. Compared with the initial values of the experiment, the 1/2GNP treatment increased soil organic matter by 7.2 g/kg and total K by 3.57 g/kg; the GP treatment increased total N by 0.76 g/kg, available N by 101.83 mg/kg, and available P by 43.97 mg/kg, respectively; 1/2 GNP and GP treatments decreased available K significantly, and increased soil pH by 0.62 and 0.60, respectively. Compared to NP treatment, 1/2GNP and GP treatment increased soil organic matter by 4.7 and 8.25 g/kg, available N by 59.33 and 36.00 mg/kg, respectively. Relative to NP treatment, 1/2GNP treatment enhanced the partial factor productivity of nitrogen fertilizer of wheat and maize by 17.6 and 14.3 percentile, and the agronomic efficiency of nitrogen fertilizer of maize and intercropping system by 5.2 and 15.3 percentile, respectively. Correlation analysis showed that wheat and maize yields were positively correlated with soil available N, available P, total N and total P, and negatively correlated with soil pH.

Conclusion Incorporating green manure to replace 50% of chemical nitrogen not only enhanced nitrogen use efficiency in wheat and maize, but also improved soil organic matter and total and available nitrogen and phosphorous contents, reduced soil pH value after over 30 years of fertilization practices, and the yield of the wheat-maize intercropping system was comparable to that achieved with full chemical fertilizer application. This demonstrates the effectiveness of long-term green manure incorporation as a sustainable crop yield and soil health management strategy.