Effects Of Annual Nitrogen Application On Soil Nutrients And Soil Microbiological Characteristics In Wheat-bean Field

This paper took the wheat-soybean double cropping farmland in Yili Valley area of northern Xinjiang as the research object,four nitrogen levels in the wheat season(NO:0 kg·hm-2,N1:104 kg·hm-2,N2:173 kg·hm-2,N3:242 kg·hm-2)and three nitrogen application levels in the soybean season(SO:0 kg·hm-2,S1:69 kg·hm-2,S2:138 kg·hm-2)were set to study the effects of annual nitrogen application on wheat soil nutrient content,soil microbial number,soil enzyme activity and crop yield under the wheat-soybean rotation system,with the aim to revealing the effects of nitrogen application in the wheat season on soil nutrient content and soil microbiological characteristics and the variation law of the nitrogen application in the wheat season on soil nutrients and soil microbiological characteristics of the subsequent crops,a nitrogen fertilizer management combination that was beneficial to improve the soil environment and increase the annual crop yield is proposed to provide a theoretical basis and technical support for the rational annual nitrogen application in Yili Valley.The main results are as follows:1.In the wheat-soybean annual rotation system,different combinations of nitrogen application had a significant effect on soil nutrients,and nitrogen application in the wheat season had after effect on subsequent soybean.The content of soil organic matter,total nitrogen,alkali-hydrolyzable nitrogen and available potassium in the season were significantly increased by applying nitrogen of 0?173 kg hm-2 in wheat season,but the available phosphorus in the soil showed a downward trend,the content of soil organic matter,alkali-hydrolyzable nitrogen and available potassium were decreased when nitrogen application amount exceeded 173 kg hm-2(N2).The annual nitrogen application had a direct impact on the soil nutrient content after soybean harvest,which is shown that on the basis of applying nitrogen from 0 to 173 kg hm-2 in wheat season,the soybean nitrogen application of 69 kg·hm-2(S1)was beneficial to increasing soil nutrients content,and improving soil fertility,no application or high application in the bean season was not beneficial to the increase in soil nutrient content;while no or moderate nitrogen application in soybean season was beneficial to the increase of soil nutrient content on the basis of 242kg·hm-2(N3)in wheat season.2.Different combinations of nitrogen application in the annual wheat-bean annual rotation system significantly affected the soil microbial area.Nitrogen application of 0?173 kg·hm-2 in winter wheat significantly increased the number of soil microorganisms and B/F,A/F values,nitrogen application of 242 kg·hm-2(N3)had an inhibitory effect,but increased soil denitrifying bacteria,and had no significant effect on the number of soil fungi and nitrifying bacteria.The higher the nitrogen application rate in the previous wheat season,the greater after effect on the subsequent crop soybeans;on the basis of nitrogen application 0?173 kg·hm-2 in the winter wheat,the application of nitrogen fertilizer 69 kg·hm-2(S1)in summer soybean could increase the number of soil microorganisms increases the B/F and A/F values;while applying nitrogen in the wheat season with 242 kg·hm-2(N3)would significantly reduce the B/F and A/F values without applying or moderate nitrogen application was beneficial to increasing the number of soil microorganisms.Therefore,nitrogen application of 104?173 kg hm-2 in wheat season and 69 kg hm-2 in soybean season is not only beneficial to the multiplication of soil microorganisms,but also to the regulation of soil microbial community structure.3.In the annual wheat-soybean annual rotation system,different combinations of nitrogen application had a significant effect on soil enzyme activity.The activities of soil catalase,urease and sucrase increased by 5.89%,27.81%and 10.53%,when nitrogen was applied at 173 kg hm-2(N2)in wheat season,however,soil enzyme activities decreased when nitrogen was applied at 242 kg hm-2(N3).Nitrogen fertilizer in winter wheat could have after effect on the change of soil enzyme activity of summer soybean;on the basis of nitrogen application in the wheat season of 0?173 kg·hm-2,soybean nitrogen application of 69 kg·hm-2(S1)could promote soil enzyme activity,no or high nitrogen fertilizer would inhibit its activity,while the application of 242 kg·hm-2(N3)in the wheat season with no or moderate nitrogen application in summer soybean was also conducive to the improvement of soil enzyme activity.4.The grain number and 1000-grain weight of winter wheat reached the highest when applied nitrogen 173 kg·hm-2(N2)in wheat season,and the average yield of winter wheat reached 7 732.22 kg·hm-2 in two years,compared with the treatment of N0,N1 and N3,the yield increased respectively 36.29%,22.11%and 6.18%.The yield of summer soybean was also significantly affected by the application of nitrogen in wheat season.On the basis of 0?173 kg·hm-2,the application of nitrogen in wheat season significantly increased the number of pods and grains per plant of summer soybean and promoted the increase of yield of summer soybean.Therefore,in the scope of this study,the application of nitrogen 173 kg·hm-2,soybean nitrogen 69 kg·hm-2 in wheat season could promote the increase of winter wheat and summer soybean yield,which was beneficial to increase the total annual yield.In summary,in the annual wheat-soybean annual rotation system,the amount of nitrogen applied to the previous crop would not only affect the soil nutrient content and microbiological characteristics of the current season,but also had a significant impact on the soil nutrient content and microbiological characteristics of the subsequent crops.The effect of nitrogen fertilizer in the wheat season would affect the level of nitrogen application in the next crop.Therefore,the optimal application of the summer soybean nitrogen fertilizer should fully consider the effect of the nitrogen fertilizer in the previous crop,and the appropriate amount of nitrogen fertilizer should be used to make full use of the nitrogen effect of the previous crop.The continuous high yield of crops was of great significance for improving soil quality and formulating a reasonable annual amount of nitrogen application.