| The increase of greenhouse gas content in the atmosphere leads to global warming,which has many adverse effects on global economy and various industries.Agriculture is the main contributor of non carbon dioxide greenhouse gases,and the development of low-carbon agriculture is an important solution to slow down the global greenhouse gas emisssion.The process of returning maize straw to the field through cattle belly is as follows;the whole-plant maize is used to make silage to feed cows,and the cow manure is returned to the maize field.It not only makes full use of the nutritional value of the whole-plant maize to produce high-quality milk products,but also realizes the return of maize straw to the field through cattle belly,which is conducive to enhancing the soil fertility.However,there is no consistent conclusion on whether manure returning to farmland can reduce greenhouse gas emisssion.In this study,maize field of a dairy farm in the north of Beijing was used for field test.Using the static box method,the greenhouse gas emission monitoring experiment of two kinds of manure with different application years(one year and five years)was carried out in a maize season.The main results are as follows:1.In the whole maize growth period,the CO2 emission of maize field which was applied manure for 5 years continuously(LM)was higher than that of maize field with SM.The average CO2 emission of LM plot was 0.58 g·m-2 h-1,and that of SM plot was 0.34 g·m-2h-1.The emission of CO2 is related to the vigorous growth level of Maize.The CH4 emission trend of the two plots was similar in the whole maize season,and it changed between source and sink.In the whole season,both treatments were weak emission sources of CH4.The average CH4 emission flux of LM plot was 0.016,and that of SM plot was 0.011.There was no significant relationship between CH4 emission and maize growth period.That was due to the high content of soil organic matter in LM plot.2.The average N2O emission of LM plot was 0.095 mg·m-2h-1,and that of SM plot was 0.39.mg·m-2-h-1.At seedling stage,the N2O emission flux of SM plot was relatively high.In the whole maize growing season,the N2O emission trends of the two blocks were different.The N2O emission of LM plot was 0.012-0.62 mg·m2-h-1.The N2O emission of SM plot increased firstly,then decreased,and gradually stabilized after seedling stage.The emission trend was similar to that of LM plot.The N2O emission of maize field was the highest at maize seedling stage,and then decreased gradually.3.In three time scales,only the emissions of CH4 and N2O were measured,and GWP of CH4 and N2O decreases with time,especially in 500a time scale.GWP of SM plot is 302.8%higher than that of LM plot on average.In 100a time scale,the global warming potential of SM and LM were 3.50 t CO2e·hm-2 and 0.86 t CO2e·hm-2,respectively.The greenhouse gas emission reduction efficiency of long-term application of manure was 75.32%.4.Applying manure to soil for a long time could increase the content of soil organic matter and water holding capacity,and reduce the content of NH4+-N 和 and NO3--N in soil,which were 19.75%and 5.59%lower than that in SM plot,respectively.At the same time,soil organic matter content was significant positive correlation with CO2 emission,but not with CH4 and N2O emission.There was a significant positive correlation between CO2 emission and N2O emission.To sum up,the study reached the above conclusions by monitoring the greenhouse gas emissions of two kinds of silage maize fields of high manure management for five consecutive years and for the first year.It has important theoretical and practical application value for popularizing the technology of manure returning to the fields. |
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