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Examining the soil microbiome structure has great significance in terms of exploring the mechanism behind plant growth changes due to maize (Zea mays L.) and soybean (Glycine max Merr.) crop rotation. This study explored the effects of soil microbial community structure after soybean and maize crop rotation by designing nine treatments combining three crop rotations (continuous cropping maize or soybean; and maize after soybean) with three fertility treatments (organic compound fertilizer, chemical fertilizer, or without fertilizer). Soil was sampled to 30 cm depth the second year at approximately the middle of the growing season, and was analyzed for physical, chemical, and phospholipid fatty acid (PLFA) profiles. Bacteria was found to be the predominant component of soil microorganisms, which mainly contained the PLFAs 16:0. Crop rotation with organic compound fertilizer application reduced the percentage of fungi in the soil by 24% compared to continuous maize and soybean with the same fertilizer application. The combination of crop rotation with organic fertilizer can reduce the percentage of fungi/bacteria to the greatest degree. In addition, the content of soil aggregate and organic matter had great influence on Gram-positive bacteria and actinomyces. In conclusion, soybean and maize crop rotation improve the soil nutrient content primarily by influencing the composition of bacterial community, especially the Gram-positive bacteria.

Legume–brassica intercropping is widely used to increase productivity in modern, sustainable agricultural systems. However, few studies have assessed the linkages between soil properties and soil microorganisms. Soil microorganisms play a key role in soil nutrient turnover and plant community composition. To elucidate the responses of soil microbial community diversity and structure to intercropping, we conducted a 2-year experiment based on common vetch (CV) monoculture, rape (R) monoculture, and common vetch–rape intercropping (IRCV) with phosphorus (P) addition in alkaline soil. The microbial communities of bacteria and fungi in the rhizosphere soil were examined based on high-throughput sequencing targeting the 16S rRNA and ITS genes, respectively. In addition, we analyzed changes in soil properties and enzyme activities. Intercropping significantly increased dry matter (up to 98.86% and 81.48%, respectively dry matter is the aboveground biomass.) compared with common vetch monoculture. Intercropping decreased soil bulk density and pH and enhanced soil available phosphorus (AP) by 14.54–34.38%, 7.25–22.67%, soil organic matter (SOM) by 15.57–22.85, 6.82–15.57%, soil sucrase (Suc.) by 13.69–16.10%, 35.57–40.24% compared to monoculture common vetch and rape, respectively. However, bacterial alpha diversity was higher under rape monoculture than IRCV. In addition, the dominant soil bacterial phyla Proteobacteria (1.25–3.60%), Gemmatimonadetes (7.88–15.16%), Bacteroidetes (9.39–11.76%), and Rokubacteria (0.49–5.69%) were present at greater abundance with IRCV relative to those with CV and R, but phyla Chloroflexi was significantly decreased by 11.56–12.94% with IRCV compared with the other two treatments. The redundant analysis showed that SOM and AP were positively correlated with the dominant bacterial and fungal flora. Common vetch–rape intercropping resulted in increased biomass and altered soil microbial community composition as well as soil properties. Our results showed that intercropping systems positively improve soil microbial activity; this strategy could help in the cultivation of multiple crops and improve soil properties through sustainable production.

Crop yield mainly depends on environment and cultivation practices that vary according to a growing environment. However, an oat (Avena sativa L.)-common vetch (Vicia sativa L.) intercrop system has not been fully developed in the agro-pastoral ecotone of Inner Mongolia, China. This study evaluated the effects of seven treatments, including five oat-common vetch intercropping patterns, sole oat, and sole vetch on yield and quality performance at different growth periods [75 days after sowing (DAS), 90 DAS, 105 DAS], on the basis of field experiments conducted in the agro-pastoral ecotone of Inner Mongolia in 2015 and 2016. The OV3:1 (oat intercropped with common vetch at seeding ratios 3:1) treatment at 105 DAS in 2016 was superior to other treatments, as it achieved the highest shoot dry matter, increasing by 24.1% and 37.1% compared to sole oat and common vetch. The crude fat (CF) contents, CF yield, and crude protein (CP) yield increased under OV3:1, and acid detergent fiber (ADF) decreased under OV3:1, compared to monoculture. The results indicate that intercropping is an efficient cropping system for the agro-pastoral ecotone of Inner Mongolia. The appropriate proportion of oat and common vetch intercropping at 3:1 and harvesting time not only increases crop yield but also improves the crop quality.

This study explores the effect of phosphorus (P) fractions, under P addition or not, based on a common vetch-rape model cropping system in alkaline soil. A two year field experiment was conducted at Tuzuo Banner modern agricultural Park in Inner Mongolia, China. Two phosphorus levels, including P0 (no fertilizer) and P45 (45 kg·ha−1 P), were performed in common vetch and rape either grown alone or intercropped. We analyzed the changes of the physicochemical properties and phosphorus fractions in the rhizosphere soil. Intercropping enhanced the common vetch and rape yield by 42.05% and 24.91%, on average, compared with corresponding sole cropping on an equivalent area basis. The average land equivalent ratio (LER) was 1.34. Intercropping had a significant AP concentration, of 65.32% and 33.99% at the P0 level, and 62.83% and 36.19% at the P45 level, respectively, compared to that of the sole common vetch and rape. With the application of P, intercropping improved the Resin-Pi and NaHCO3-Pi fraction (61.17%, 87.03% at the P0 level and 96.50%, 41.85% at the P45 level, compared to monocropped common vetch and rape in 2019). The changes in NaOH-Pi and NaOH-Po (except for NaOH-Pi in 2019) showed no significant difference between cropping systems. Intercropping significantly accumulated concentrations of HCl-P, while depleting Residual-P, in 2020. In conclusion, common vetch/rape with the addition of P polyculture stimulated rhizosphere soil P mobilization and had a yield advantage over sole cropping.