Effects Of Reduced Nitrogen Application And Sweet Maize//Soybean Intercropping On Nitrogen Balance In Farmland

Because of high nutrition and good palatability,sweet maize?Zea mays L.saccharata sturt?is becoming more and more popular.Guangdong Province is the most important region for sweet maize production in China.However,continuous sole sweet maize cropping combined with high chemical nitrogen?N?fertilizer application may lead to serious nitrogen pollutions.Those problems become more severe during the growth season and after harvesting when cropping two or three sweet maize seasons in a year,because the N fertilizer application is almost doubled than one maize cropping season.Here,a field experiment of 2 years and 4 seasons was conducted on the basis of field location test in 5seasons in 3 years was conducted to assess the influence of four different cropping systems[sole sweet maize?SS?,sole soybean?SB?,two rows sweet maize-three rows soybean?S2B3?intercropping,and two rows sweet maize-four rows soybean?S2B4?intercropping],together with two rates of N fertilizer application to sweet maize[0?N0?,300?N1?and 360?N2?kg N·hm^-2)]on crop agronomic trait,crop productivity,soil greenhouse gas?CO₂ and N₂O?,N balance.In order to optimize the sustainable and environmentally friendly production of sweet maize in south China.The main results were as follows:1.It has no negative effect on sweet maize agronomic trait to intercrop with soybean.But,the agronomic characters and yield per plant of sweet maize at N0 level were significantly lower than those of N1 and N2.There was no significant difference between the two nitrogen levels.There were no significant effects on agronomic traits and yield per plant of soybean by intercropping pattern and nitrogen application level.But the N fixation efficiency and nitrogen fixation of soybean were decreased at N1 and N2 levels in sweet maize//soybean intercropping.2.Although the grain yield of intercropping sweet maize and soybean system was lower than the corresponding monoculture,but different intercropping system of land equivalent ratio greater than 1,the actual yield loss index of more than 0.Long-term continuous sweet maize//soybean intercropping can increase crop yield and land use efficiency,and the N0 level of intercropping the advantage of the highest,while decreased with the increase of nitrogen level.Planting pattern and nitrogen application level have no significant effect on the stability of sweet maize yield,but the sweet maize//soybean intercropping pattern could improve the stability of soybean yield and total yield of the system.3.The application of nitrogen could reduce the emission flux of CO₂ and increase the rate of soil nitrification and the flux of N₂O.Soil nitrification is the main process of N₂O production in farmland.Sweet maize//soybean intercropping could reduce the cumulative emission flux of N₂O from soil,but had no significant effect on the cumulative emission flux of CO₂.Reducing nitrogen application and sweet maize//soybean intercropping could reduce the greenhouse gas emission intensity,and the greenhouse gas emission intensity of S2B4-N1 is lower than that of other treatments.The results showed that S2B4-N1 could not only maintain crop productivity but also reduce greenhouse gas emissions of soil effectively.It is an environment-friendly sweet maize planting model.4.In most cases,sweet maize//soybean intercropping can reduce ammonia volatilization and nitrogen leaching amount,the main pathways of nitrogen loss in the agricultural system,and reduce their impacts on the environment.The nitrogen balance of sweet maize monoculture and intercropping mode in the both of N1 and N2 level was nitrogen surplus.The annual nitrogen surplus of sweet maize monoculture was more than300 kg·hm^-2,which was higher significantly than that of sweet maize and soybean intercropping,what was extremely easy to cause the nitrogen loss and environmental pollution.The annual nitrogen surplus of sweet maize intercropping was lower than 100kg·hm^-2,so that the agricultural system maintained the soil nitrogen balance basicly,it can not only maintain soil fertility,ensure the normal growth crop,save the production cost,but also reduce the pollution of the environment.Sweet maize//soybean intercropping is an efficient,energy saving and environmentally friendly planting pattern.5.There was no significant effect of nitrogen application level and planting pattern on the infection rate and infection intensity of mycorrhizal fungi in sweet maize.In the intercropping model,the mycelium of arbuscular mycorrhizal fungi could transfer nitrogen fixed by biological nitrogen fixation of soybean to the adjacent zone of sweet maize//soybean,at the same time,arbuscular mycorrhizal fungi could help soybean activate and transport phosphorus of the soil,meet the needs of soybean growth and nodulation nitrogen fixation for phosphorus.The intercropping pattern of sweet maize//soybean also promoted the absorption of nutrients,which was one of the factors that showed the advantage of intercropping.