Effect Of Different Tillage Measures On Nodulation, Nitrogen Fixation And Growth Of Summer Soybean

Tillage measures are the most common way to affect the crop growth environment by changing the soil structure.Among them,conservation tillage is considered to be a sustainable agricultural management measure to replace traditional tillage,which can maintain soil structure,steadily improve the ability of farmland soil in arid areas to store water and moisture,improve the composition of soil microbial community and living environment,and continuously improve farmland soil fertility and yield stability.Root nodules are an important site for symbiotic nitrogen fixation in leguminous crops.Nitrogen（N₂）in the atmosphere is converted into nitrogen nutrients that can be absorbed by crops under the action of nitrogenase in the nodules.This not only reduces the dependence of soybeans on artificial nitrogen application,but also improves their stable yield ability in case of fertilizer shortage.However,in current research,the extent and principle of changes in nitrogen fixation activity during soybean biological nitrogen fixation process under conservation tillage are not clear.This study is a long-term conservation tillage experiment that has been ongoing since 2009.It was conducted on the experimental field of Northwest A&F University of Science and Technology in Yangling District,Xianyang City,Shaanxi Province.The experimental treatments included two types of conservation tillage（Chisel Plough Tillage-CPT,Zero Tillage-ZT）and traditional tillage（Plow Tillage-PT）,this article compares the effects of tillage measures on soil moisture changes from 0 to60cm,soil physical structure,and rhizosphere soil nutrient content through experimental data from soybean seasons in 2021 and 2022.It analyzes the growth and development status of soybean nodules during the growth period and the response of nitrogen fixation characteristics changes to tillage measures.Combined with experimental results such as yield and yield components during soybean maturity under different tillage treatments,The aim is to provide scientific basis for the selection of cultivation measures in soybean production in the arid agricultural area of the Guanzhong Plain.The main results of this study are as follows:（1）Farming measures significantly affect soil moisture content,aggregate distribution,and aggregate stability in soybean fields.Compared to PT,CPT and ZT increased soil moisture content by 9.47%and 14.38%in 0～10 cm soil,aggregate content>0.25 mm by 44.64%and 47.07%,respectively.At the same time,they increased GMD of soil aggregates by 47.31%and 58.92%,as well as MWD by54.07%and 75.09%,respectively,in 0～20 cm soil.In addition,CPT and ZT significantly increased the nitrate nitrogen content of 38.00%and 41.69%,ammonium nitrogen content of 29.78%and 17.19%,and total nitrogen content of 56.83%and54.29%in the rhizosphere soil of summer soybean.（2）Different tillage measures have a significant impact on the nitrogen accumulation in the root system of soybean in the early growth stage,as well as the content and composition of leghemoglobin at each stage.Although tillage measures have no significant impact on the changes in root biomass,CPT significantly increased the dry weight of root nodules by 14.96%before the bulging stage.Compared to PT,CPT reduced the Green Lb content by 30.23%,increased the Lb content by 18.41%and the Red Lb content by 40.32%during the pod setting period;ZT increased the Lb content by 10.50%and the Red Lb content by 13.89%after the granulation period,but it increased the content of Green Lb by 12.52%.During the pod setting period,the content of Red Lb is highly significantly positively correlated with nitrate nitrogen（0.956**）and ammonium nitrogen（0.903**）,while the content of Lb is significantly positively correlated with nitrate nitrogen（0.731*）and ammonium nitrogen（0.761*）.However,the content of Green Lb is not significantly correlated with both nitrate and ammonium nitrogen.（3）The cultivation measures did not significantly affect the nitrogen absorption,biomass,and yield of soybean aboveground,but compared to PT,CPT and ZT treatments significantly increased the total nitrogen content of grains by 3.26%and 2.06%,as well as the nitrogen harvest index by 8.60%and 7.56%.In conclusion,CPT and ZT reduced the disturbance to soil structure,improved the physical and chemical properties of soil,created a soil environment suitable for crop growth and microbial survival,had a positive impact on the growth and development of summer soybean nodules and the improvement of biological nitrogen fixation capacity,and increased the total nitrogen content and nitrogen harvest index of seeds.Therefore,in the Guanzhong Plain,conservation tillage,especially CPT,is a reasonable tillage method suitable for the summer soybean planting system in arid agricultural areas.