Responses of productivity to film mulching patterns and chemical fertilizer application rates in maize||pea intercropping system

To investigate the response of productivity to mulching patterns and chemical fertilizer application rates in intercropping and monoculture cropping systems, we conducted a long-term maize||pea intercropping field experiment at the Zhangye Water-saving Agricultural Experimental Station of the Gansu Academy of Agricultural Sciences. The experiment began in 2012 and consisted of three factors. The first factor was film mulching patterns, including strip mulching and full mulching. The second factor was chemical fertilizer application rates, including conventional fertilization with 450 kg(N)·hm⁻² and 78.6 kg(P)·hm⁻² and reduced fertilization with 300 kg(N)·hm⁻² and 52.4 kg(P)·hm⁻². The third factor was cropping systems, including maize monoculture, pea monoculture, and maize||pea intercropping. Plant samples were collected at the harvest stage of pea and maize in 2021 and 2022, and the grain yield, aboveground biomass, crude protein yield (calculation based on grain nitrogen concentration), and phosphorus uptake of grains were measured. The results showed that the yield of the intercropping system was the highest; the grain yield of the intercropping system was significantly higher than that of the weighted mean of the monoculture system by 31.9% in the two years, mainly because of the positive complementarity effect rather than the selection effect. In addition, the land equivalent ratio was greater than 1 in each treatment, indicating that intercropping exhibited a greater land-use efficiency than monoculture. On the average, for the two experimental years, compared with monoculture, intercropping increased the grain crude protein yield and phosphorus content by 30.0% and 24.0%, respectively. Full mulching significantly enhanced productivity and crude protein yield compared with strip mulching. Compared to monoculture combined with strip mulching, intercropping with full mulching significantly increased grain yield, crude protein yield, and partial productivity of nitrogen and phosphorus fertilizers by 47.0%, 57.5%, 47.5%, and 47.3%, respectively. The yield of intercropping treatment was 38.4% and 26.3% higher than that of monoculture under strip mulching and full mulching treatments, respectively. Under monocropping and intercropping conditions, the yield of mulching was 15.9% and 5.8% higher than that of strip film, respectively, that is, intercropping combined with full mulching enhanced nutrient use efficiency. There was no significant difference in yield between the two fertilization levels. Under reduced NP chemical fertilizer treatment, intercropping system increased the partial productivity of fertilizer and maintained productivity and crude protein yield compared with conventional fertilizer application rate. In conclusion, intercropping under reduced fertilization with full-film mulching is more sustainable than the conventional practice of farmers (i.e., maize monoculture with conventional fertilization under strip mulching), because it enhances productivity and saves chemical fertilizer.