Search

It has been established that maize/soybean intercropping can improve nitrogen use efficiency. However, few studies have addressed how maize/soybean intercropping affects nitrogen-fixing bacterial diversity and N fixation efficiency of intercropped soybean. In this study, nitrogen-fixing bacterial communities, N fixation efficiency, and their relationships with soil properties under three nitrogen fertilization application rates (N0 0 kg/ha, N1 40 kg/ha, N2 80 kg/ha) were explored through field experiments. Nitrogen fixation and nitrogen-fixing bacteria diversity were assessed using 15N natural abundance, Illumina high-throughput sequencing, and nifH (nitrogen fixation) gene copies quantification in the rhizosphere soil of intercropped soybean. The results showed that nitrogen application rates significantly decreased the nitrogen-fixing bacteria diversity, nitrogen fixation efficiency, and nifH gene copies in the rhizosphere soil. Nitrogen fixation efficiency, nodule number, and dry weight of intercropped soybean were highest in the N0 treatment, and nitrogen fixation was the highest in the N1 treatment. The nitrogen-fixing efficiency in N0, N1, and N2 treatments increased by 69%, 59%, and 42% and the nodule number of soybean was 10%, 22%, and 21%, respectively, compared with monocultures. The soybean nitrogen-fixing bacteria diversity in intercropping under N0 and N1 treatments significantly increased compared with monocultures. There was a significant positive correlation between soil nifH gene copies and N fixation efficiency and a negative correlation with soil available nitrogen. Bradyrhizobium abundance in soybean rhizosphere soil decreased significantly with the increase in nitrogen application rates and was significantly correlated with soil AN (available nitrogen) and pH content in the soybean rhizosphere. These results help us to understand the mechanisms by which nitrogen use efficiency was improved, and nitrogen fertilizer could be reduced in legume/Gramineae intercropping, which is important to improve the sustainability of agricultural production. [ABSTRACT FROM AUTHOR]

Global demand for food continues to grow as a result of rising incomes and population growth. Meanwhile, the sustainability of food production is affected by climate change and agricultural soil degradation. The objective of this study was to evaluate the dynamic changes of maize/soybean yield, yield stability and soil fertility under mono-cropping and intercropping systems with different nitrogen application rates. The yield stability and sustainability of maize and soybeans were studied from 2017 to 2020 (Northeast Agricultural University, Acheng Experimental Site) according to the changes in crop yield, actual yield loss index, soil fertility over time as well as the differences in coefficient of variation and sustainable yield index under different cropping patterns in the maize/soybean intercropping system. This study established three cropping patterns (maize monoculture, soybean monoculture, and maize/soybean intercropping) with four nitrogen application rates (0/0 kg N ha–1, N0; 180/40 kg N ha–1, N1; 240/80 kg N ha–1, N2; 300/120 kg N ha–1, N3) based on the two-factor split block design. The maize and system yield indicated that intercropping was superior to the corresponding monoculture throughout the four-year experiment. With the extension of planting season, the yield from intercropping with nitrogen treatment (N1, N2 and N3) was higher than that without nitrogen treatment (N0). The yield stability of the intercropping system was also higher than that of the matched monoculture system. The coefficient of variation of the intercropping system was 18.83 % on average, which was lower than that of the matched monoculture system. In four years, the average contribution rate of soil fertility in intercropping treatment was higher than that in monoculture treatment. The structural equation model results suggested that the effect of nitrogen application rate on yield and yield stability was greater than that of cropping pattern. The yield and yield stability of maize/soybean intercropping over time was higher than matched monoculture under different nitrogen application rates due to higher soil fertility contribution in intercropping. This study provides theoretical evidence for maintaining the sustainability of legume and cereal intercropping and improving food security in the increasingly intensive global cropping systems. • Maize/soybean intercropping over time improved stability of crop yields. • Soil fertility contribution rate in intercropping was higher compared to monoculture. • Contribution rate of N fertilizer to maize yield stability was greater than soybean. • Influence of fertilizer on yield stability was greater than that of cropping pattern. [ABSTRACT FROM AUTHOR]