The Nitrogen Transformation And Utilization In Lime Concretion Black Soil Region And Their Responses To Different Nitrogen Application Rates

Lime concretion black soil is a typical low-yielding fields in China.The lime concretion black soil has heavy clay structure,poor permeability,which lead to the effective nutrient supply imbalance,low supplying capacity of soil nutrient and production performance.To the best of our knowledge,soil microbes play a predominant role in soil nitrogen transformation process.To provide scientific basis for directional adjustment to control soil nitrogen transformation process,improve nitrogen use efficiency and reduce its negative effects,nitrogen transformation process and mechanism driven by soil microorganisms were studied.This experiment was carried out to study the change characteristics of actions intensity of soil nitrogen transformation microorganisms and activity of enzymes,dynamic changes of soil nitrogen mineralization and ammonia volatilization,effects of physical and chemical factors on soil nitrogen transformation and absorption and utilization of nitrogen in Wheat.The effects of different nitrogen application rates on nitrogen transformation characteristics and nitrogen utilization in wheat field had been systematically studied.Under the action of soil nitrogen transformation microbes and related enzymes,soil nitrogen transformation produced significant changes in the whole growth period of winter wheat.There is a close relation between the soil nitrogen transformation and soil nitrogen,organic carbon,temperature and moisture,affecting the capacity of nitrogen supply in soil,and affect wheat on soil nitrogen absorption and utilization.The main achievements of our studies are as following:In the whole growing period of Winter Wheat in the lime concretion black soil,the intensity of soil nitrogen transformation(except denitrification intensity)and enzyme activity increased first and then decreased.The difference is that,the activity peak of ammoniation intensity,nitrification intensity and protease appeared in flowering stage,and urease activity peak appeared at jointing stage.The highest value of denitrification intenstiy was reached at the jointing stage during the whole growth stage,and then increased at first and then increased after the jointing stage,the valley value appeared at the flowering stage.Application of nitrogen fertilizer couldsignificantly increase the intensity of soil nitrogen transformation microbial activity and enzymes activity,but excessive nitrogen had inhibitory effect on ammonification intensity,nitrification intensity,denitrification intensity and protease activity.Ammonia volatilization rate of wheat field,soil net mineralization rate and soil net nitrification rate changed significantly during the whole wheat season.There were two peaks of the soil net nitrogen mineralization rate and net nitrification rate at over winter stage and flowering stage,respectively.Compared with the over winter stage,the peak value of the soil net nitrogen mineralization rate and net nitrification rate increased by 70% and 100% at the flowering stage,respectively.There were three peaks of the ammonia volatilization rate during 21~33 d after sowing,146~149 d after sowing,and 219 d after sowing.,there was a process of ammonia concentration release in the winter wheat field,the total amount of ammonia volatilization during the 21~33 d after sowing is 35.4% of the total accumulated amount of the whole growing period.With the increase of the amount of nitrogen fertilizer,the ammonia volatilization of the wheat field in the lime concretion black soil was increased.Increasing N application rate was benefit to the increasing of the net N mineralization rate and the net nitrification rate,but excessive nitrogen application could inhibit the increasing of net N mineralization and net nitrification rate.The content of soil organic carbon,ammonium nitrogen and nitrate nitrogen increased first and then decreased,and reached the highest level at heading stage or flowering stage.While the total nitrogen content in the soil had two small peak at heading stage and grain filling stage,respectively.The increasing of nitrogen fertilizer is beneficial to the improvement of soil organic carbon,total nitrogen,ammonium nitrogen and nitrate nitrogen content.But when the amount of nitrogen fertilizer increased to 330 kg?hm-2,soil ammonium nitrogen content continued to increase,soil total nitrogen,nitrate nitrogen content was maintained at the level of N225,while the soil organic carbon content declined.Excessive nitrogen application also resulted in a decrease of soil C / N ratio,which was unfavorable to the net N mineralization.There was a very significant positive correlation between soil organic carbon content and number of ammonification intensity,nitrification intensity,urease and protease activity.There was a significant negative correlation between soil total nitrogen content and nitrification intensity,but there was a significant positive correlation between the strength of denitrification.There was a significant positive correlation;between soil SOC/TN and ammonification and nitrification intensity.Soiltemperature had great influence on the intensity of ammonification and nitrification intensity,and the soil moisture content has great influence on the activity of urease and protease.The physical and chemical properties of soil had significant effect on the microbial interaction strength and the enzyme activity of soil nitrogen transformation,and then produced influence to the soil nitrogen transformation process.Ammonification intensity is closely related to ammonia volatilization;soil net N mineralization rate,net nitrification rates were significantly affected by Ammonification intensity,nitrification intensity,urease and protease activity.While the increasing of nitrogen fertilizer is the key to increase the yield of Winter Wheat in the lime concretion black soil.There was no significant improvement of excessive nitrogen application on wheat yield,and reduced nitrogen fertilizer use efficiency,increase the residual nitrogen in soil and straw.Winter wheat yield and plant nitrogen accumulation increased with the increase of nitrogen application rate.Compared with N0 treatment,the yield and plant nitrogen accumulation increased by240.0% and 334.8%;191.0% and 402.3%,respectively.When the nitrogen application rate increased to 330,the plant nitrogen accumulation rate increased by28.2% compared with the N225 treatment,while the yield increased by only 1.1%.With the increase of the amount of nitrogen application,NHI,NUPE and PFPN gradually decreased,NUE performance for N225>N330>N120,the NUE of N225 treatment was 1.33 times and 1.08 times of N120 and N330 treatment,respectively.With the increase of the amount of nitrogen fertilizer,the content of soil ammonium nitrogen and soil nitrate nitrogen in the lime concretion black soil was increased in different degree,too.Winter wheat root system was concentrated in 0-40 cm soil layer in the lime concretion black soil.After nitrogen fertilizationis,under the action of irrigation and rainfall,the mineral nitrogen moved down,the accumulation of ammonium nitrogen and nitrate nitrogen in deep soil increased gradually.With the increase of the amount of nitrogen application,the trend of soil ammonium nitrogen and nitrate nitrogen content in deep soil is more obvious.But in deep soil,the nitrogen uptake capacity of wheat is limited,which led to the residual nitrogen in soil.