Effect of nitrogen amendment and straw-stubble input on accumulation of soil organic matter in typical farmlands of Huang-Huai-Hai Plain

Soil organic matter plays a crucial role in soil fertility,environmental protection and sustainable development of agriculture.Inventory of soil organic carbon is necessary for the development of strategic policies regarding to the global agricultural production and environmental change.Carbon sequestration is very important not only to improve soil quality and increase economic crop production,but also to increase soil carbon storage for carbon trading and mitigating CO2 emissions from the soil profile.Much attention has been paid to global carbon cycle because of the emergence of a series of environmental problems such as the increase in atmospheric CO2 concentration and global warming.More than twice as much carbon is held in soils as investigation,and changes in soil carbon content can have large effects on the global carbon budget in the atmosphere.Thus,increasing soil organic matter content is of great importance for the sustainable development in China and the entire world.Various management practices on agriculture land can have an impact on soil carbon content.Agricultural practices that affect soil carbon include tillage system,cropping system,N fertilization,and many others.Agricultural management practices such as tillage,rotation and fertilization influence soil organic matter dynamics after long term cultivation to a large extent.Nitrogen application can have a significant effect on soil organic carbon pools and plant biomass production,but it is not convincingly clarified whether nitrogen fertilizers increase or decrease soil organic matter at certain agricultural conditions.The objective of this paper was to explore the relationship between carbon-nitrogen application and the accumulation of soil organic carbon.The experimental data were mainly obtained from in ten long-term fertilization trials at different locations.This paper evaluated the change of soil organic matter in relation to input of straw-stubble organic carbon and nitrogen amendment.All long-term trials were located in an important grain production area of China,the Huanghuaihai Plain,and the duration of the trials varied between 5 and 15 years.The results have shown that the relationship between the accumulation of soil organic matter and straw-stubble amendment was significantly affected by nitrogen fertilizer rate.Both HNPK(fertilizer nitrogen rate330 kg/(hm2·a))and NPK(fertilizer nitrogen rate ≤330 kg/(hm2·a))have influenced the relationship between the amount of straw-stubble amendment and the change of SOM significantly(P0.01).When the carbon of straw-stubble amendment was the same,the annual average of soil organic matter accumulation in HNPK treatment was significantly smaller than in NPK treatment.When fertilizer nitrogen use was higher than 330 kg/hm2 a(HNPK),the amount of straw-stubble amendment necessary to maintain soil organic carbon(MSC)was 7254 kg/(hm2·a),while it was 1297 kg/(hm2·a)in the NPK treatment.The former was 5.6 times more than the latter.In summary,overuse of nitrogen fertilizer largely decreased the net accumulation of soil organic carbon and had negative impact on improvement of soil organic matter.