Microbial-Mediated Nitrogen Variations and Yield Performances in a Soybean–Maize Strip Intercropping System Under Whole-Field Film Mulching

The soybean–maize strip intercropping system enhances soybean yield while maintaining maize production, improving nitrogen use efficiency, and fostering intercropping mutualism. However, vigorous weed growth in warm and humid regions competes for nitrogen, while elevated soil temperatures accelerate nitrification, promoting nitrogen loss, especially during the peak nitrogen demand period of maize. Plastic film mulching, which conserves moisture, regulates temperature, and suppresses weeds, can improve the soil environment. A two-year field experiment was conducted with polyethylene (PE) films of various thicknesses (0.01, 0.014, 0.02 millimeters) and colors (black, white, silver-black) with an un-mulched control plot. Soil nitrogen content, microbial diversity, soil properties, and crop productivity were analyzed. The results indicated that plastic film mulching significantly altered soil nutrient availability and rhizosphere microbial community structures, while simultaneously enhancing crop productivity. The 0.014 mm black and white films performed best, showing a positive association with enhanced nitrogen transformation indices, which coincided with increased available nitrogen, biomass, and crop yield. However, long-term soil nutrient depletion remains a risk, suggesting the need for strategies like organic fertilizers or crop rotation to maintain soil fertility and ecological sustainability.