Effects Of Intercropping And Rotation Between Mung Bean And Gramineous Crops On The Potential Of Reducing Nitrogen Application And Cadmium Uptake

China’s consumption of nitrogen fertilizer accounts for about 30% of the world’s total,and it is the largest country in the use of nitrogen fertilizer.Previous studies have shown that legumes//Gramineae can use nodule nitrogen fixation of legumes to reduce nitrogen application,but the most suitable nitrogen application rate for each crop has not been indicated.The pollution of heavy metal cadmium in China is becoming more and more serious.One of the causes of pollution is environmental pollution caused by excessive nitrogen application.Previous studies have shown that intercropping can reduce the absorption and transport of cadmium by crops,but through intercropping needs to be further studied whether reducing nitrogen application can further reduce the harm of cadmium,and whether reducing nitrogen application will affect the changes of crop rhizosphere microbial community needs to be studied,so this experiment is based on this.The results showed that mung bean and maize could alleviate the effect of reducing N application on the biomass of mung bean and maize;Mung bean and corn increased the land equivalent ratio by 1.2-1.5,which improved the production efficiency;Mung bean / / maize alleviated the reduction of N content in roots / stems / leaves / grains of maize;Compared with monoculture maize,monoculture of mung bean and mung bean / maize could increase soil p H.The results showed that under the premise of ensuring the yield,the intercropping mode could reduce the application of nitrogen fertilizer to achieve the purpose of reducing fertilizer.(1)Three planting patterns and four nitrogen application rates were set up in the field experiment.The three planting patterns were wheat-mung bean(P1),wheat-maize(P2),wheat-maize//mung bean intercropping(P3).The four nitrogen gradients were conventional nitrogen application(CK),85% of conventional nitrogen application(N1),70% of conventional nitrogen application(N2),and 50% of conventional nitrogen application(N3).Three replicates were set for each planting pattern,with a total of36 plots,the biomass,yield,total nitrogen content and soil p H of mung bean,maize and wheat were studied under different planting patterns and nitrogen application rates.(2)Three planting patterns and five nitrogen application rates were set up in pot experiment.The three planting patterns were as follows: one maize and one mung bean in the pot,with PVC board(SB),nylon net(MB)and non barrier(NB)in the middle.The five nitrogen application rates were CK,85% of conventional nitrogen application(N1),70% of conventional nitrogen application(N2)and 50% of conventional nitrogen application(N3),no nitrogen application(N4),normal application of p Hosphorus and potassium,and no reduction,five replicates were set for each treatment,a total of 75 pots.The changes of biomass,cadmium content,enrichment coefficient,transport coefficient,available Cd content in rhizosphere,p H and nitrogen content in rhizosphere of mung bean and maize under different intercropping patterns and nitrogen application rates were studied.The results showed that reducing N application could significantly reduce Cd uptake and accumulation by crops;The interaction between maize and mung bean roots inhibited the uptake of Cd by maize and mung bean;The interaction between maize and mung bean roots could alleviate the decrease of enrichment coefficient and change the transport coefficient of maize and mung bean;With the decrease of N application,legumes increased the contents of total N and alkali hydrolyzable N in rhizosphere soil,which may be related to legume nitrogen fixation.In addition,interaction with maize roots can increase the N fixation capacity of mung bean.In conclusion,reducing nitrogen application can reduce cadmium uptake by crops.(3)The rhizosphere soil of mung bean and maize was collected by pot experiment,and the microbial community structure of each treatment was analyzed by high-throughput sequencing,According to the changes of microbial community,it can be seen that Chloroflex,Proteobacteria,actinobacteriota and acidobacteriota are the dominant bacteria of mung bean and maize,there was no significant change in the abundance of each phylum in the same crop under the same planting pattern and different nitrogen application rates.PCo A analysis showed that mung bean significantly affected rhizosphere bacterial community composition,while maize had no significant difference.RDA analysis showed that there were significant positive or negative correlations between mung bean and Maize in terms of Campylobacter,proteus,actinomycetes,acidobacteria,total nitrogen content in rhizosphere soil,Cd content in root,available Cd content in rhizosphere soil and p H in rhizosphere soil,but the relationship between Mung bean and corn is not consistent,which indicates that the rhizosphere environment of the two crops is different.