Effects Of Nitrogen Application Level On Soil Nitrogen Fractions And Maize Growth

Heilongjiang Province is the main production area of spring maize in China,with corn of 54.8million hectares and output of 34.64 million tons in 2020,accounting for percent and 13 percent of the national total,respectively.Crop rotation and continuous cropping are the main cultivation methods of maize,and improving maize yield is an important part of national food security.Maize is a high light efficiency C4 plant,which requires a wide variety of fertilizers in the growth process,among which the most important nutrient element is nitrogen.And the application of nitrogen fertilizer can promote the growth of the upper part of maize ground and change the root to crown ratio.Nitrogen in soil is the main factor affecting plant growth and productivity of farmland ecosystems.Nitrogen mainly exists in the form of soil organic nitrogen in the soil surface layer.Application of nitrogen fertilizer can change the content of soil nitrogen components and enhance soil nitrogen supply capacity,and the application of appropriate amount of nitrogen fertilizer can promote maize yield formation.In contrast,excessive application of nitrogen fertilizer will reduce nitrogen use efficiency rate and the effect of yield increase will not be significant.Therefore,the study of the nitrogen application level on soil nitrogen components and maize growth can provide theoretical basis and reference for scientific nitrogen fertilizer application and efficient maize production.This experiment was conducted in 2021 at the experimental and practical base of Northeast Agricultural University in Xiang yang,using a locational trial field started in 2015.Four nitrogen application levels were set under continuous cropping(C)and maize-soybean rotation(R)cropping modes.Urea application rates were 0(C0),180 kg/hm~2(C180),360 kg/hm~2(C360)and540 kg/hm~2(C540)under maize continuous cropping,respectively.Under maize-soybean rotation treatment,urea application rates were 0(R0),180 kg/hm~2(R180),270 kg/hm~2(R270),360 kg/hm~2(R360)in maize planting season,respectively.Urea application amounts were 0,29 kg/hm~2,58kg/hm~2and 88 kg/hm~2in soybean planting season,respectively.The effects of nitrogen application level on soil nitrogen components and maize growth were studied by measuring soil nitrogen components,related photosynthetic parameters,nitrogen use efficiency and yield.The results showed that:(1)Under rotation and continuous cropping,the content of soil available nitrogen increased significantly with the increase of nitrogen application rate.Under rotation,the soil available nitrogen content reached the maximum value before spring sowing and after autumn harvest in R360 treatment,and reached the maximum value before spring sowing and after autumn harvest in C540 treatment under continuous cropping.The soil available nitrogen content in 0-15 cm layer was higher than that in 15-30 cm layer.The content of nitrate and ammonium in soil also showed consistent regularity.(2)Under rotation and continuous cropping,soil nitrogen content increased with the increase of nitrogen application rate.Under rotation,except for acidolytic unknown nitrogen and microbial nitrogen,soil nitrogen content reached the maximum in R360 treatment.Under continuous cropping treatment,except microbial nitrogen,non-acidolytic nitrogen and acidolytic ammonia nitrogen,all reached the maximum value at C540 treatment.Under crop rotation,the contents of total nitrogen,microbial biomass nitrogen,acidolized ammonia nitrogen,amino acid nitrogen and non-acidolized nitrogen in 0-15 cm soil layer were higher than those in 15-30 cm soil layer.Under continuous cropping treatment,the contents of total nitrogen,microbial biomass nitrogen,acidolytic ammonia nitrogen,amino acid nitrogen and amino sugar nitrogen in 0-15 cm soil layer were higher than those in 15-30 cm soil layer.(3)Under rotation and continuous cropping,the nitrogen accumulation in shoot increased with the increase of nitrogen application rate.Under rotation,the nitrogen accumulation in stem,leaf,grain and cob reached the maximum value under R360 treatment.The nitrogen accumulation of stem and leaf,grain and cob under continuous cropping treatment reached the maximum value under C540 treatment,and the difference between treatments was significant.(4)Under rotation and continuous cropping,the relative chlorophyll content of maize leaves and the effective quantum yield of photosynthetic systemⅱincreased firstly and then decreased from jointing stage to waxing stage,and increased with the nitrogen application rate.However,the difference between nitrogen application rates was not obvious.The quantum yield of regulatory energy dissipation and proton dynamic potential of maize leaves increased with nitrogen application rate from jointing stage to waxing stage(5)Under rotation and continuous cropping,plant height,stem diameter,dry matter weight of aboveground and yield of maize increased with the increase of nitrogen application rate.and reached the maximum value in R360 treatment under rotation,while reached the maximum value in C540 treatment under continuous cropping.