Effects and evaluation of planting density on population yield and mixed silage quality of silage maize soybean strip intercropping in the irrigation area of Northern Xinjiang, China

Using the ‘Denghai 618’ high-yielding silage maize variety and ‘Jiyu 441’ shade-tolerant, collapse-resistant soybean variety from the Northwest Irrigation District in China as materials, a two-factor split-zone design was used to comprehensively analyze the differences between maize planting density (2021: 67 500, 82 500, 97 500 plants·hm⁻²; 2022; 90 000, 105 000, 120 000 plants·hm⁻²) and soybean planting density (2021: 120 000,150 000,180 000 plants·hm⁻²; 2022: 150 000,180 000,210 000 plants·hm⁻²) on the population yield and silage quality of silage maize-soybean strip intercropping. Maize planting density of 105,000 plants·hm⁻² produced the highest yield, which was 23.44% and 10.56% higher than that of 90,000 and 120,000 plants·hm⁻², respectively. Soybean planting density of 150,000 plants·hm⁻² produced the highest yield of 14.15 t·hm⁻². Population yield under the combination of maize 105 000 and soybean 210 000 plants·hm⁻² was highest (64.98 t·hm⁻²), which was 11.97 t·hm⁻² higher than the minimum planting density treatment (maize density 90 000 plants·hm⁻², soybean density 150 000 plants·hm⁻²), and 3.49 t·hm⁻² higher than the net cropping of maize at the same planting density. The regression equations fitted to the regression equations yielded maize and soybean planting densities of 109,600 and 105,000 plants·hm⁻², respectively. The crude protein content reached a maximum of 12.23%, and the forage grading index (GI) reached a maximum of 36.52. The values represented percentage and GI increases of 2.39% and 36.52%, respectively, compared with those of the same density of net-crop corn. The 2.39% and 22.55% increase in the GI, and the differences in acid and neutral detergent fiber contents and relative feeding value under the strip intercropping pattern were not significant (P > 0.05) compared with that of net-crop maize at the same density. Grey correlation analysis comprehensively evaluated the biological yield and silage nutritional quality of each treatment. The weighted correlation of ranks 1 and 2 was 0.8900 and 0.8723, respectively. The results indicate that the high-yielding and high-quality planting density combinations of silage maize-soybean strip-cropping in the northern frontier irrigation area of maize density 105,000 and soybean density 150,000 plants·hm⁻², followed by maize density 82,500 and soybean density 180,000 plants·hm⁻², can be popularized and applied in suitable areas.