Ammonia,greenhouse Gas And Soil Orgamic Carbon Response To Agricultural Management Practices

Different agricultural managements have important effect on soil greenhouse gas emission,ammonia volatilization,soil structure and different soil organic carbon pools.Application of different type of fertilizers is the most direct way to improve the efficiency of agricultural production,but also can cause a series of environmental problems,such as greenhouse gase emission,ammonia volatilization,soil structure degradation,soil physical and chemical properties degradation and the change of soil fertility,etc.Soil nitrogen cycling and the change of soil structure are not only related to fertilizer type,ratio of nutrients,but also related to land use and the growth of different plant type.Therefore,study and reveal the response of fertilizer type,ratio of nutrients and land use to soil carbon and nitrogen cycling and soil structure has great significance to guide agricultural production.This research includes three parts:first part,we studied the effect of different fertilization methods on greenhouse gas emission and ammonia volatilization.A long-term wheat experiment in southern Louisiana was selected as the study object.The study include seven fertilization treatments:CK-No fertilizer was applied,U-one time application of urea at112 kg N ha^-1,CU-polymer coated urea application at 112 kg N ha^-1,SU-split applications of urea at 56 kg N ha^-1 each time,SASU-split application of urea and ammonium sulfate,both at56 kg N ha^-1,U+N-application of urea with urease inhibitor（NBPT）at 112 kg N ha^-1 and U+D-application of urea with nitrification inhibition（DCD）at 112 kg N ha^-1.The effects of different fertilizer type at same application rate on soil carbon and nitrogen turnover were analyzed by observing the soil greenhouse gas emission and ammonia volatilization during wheat growing season.The second part,the effect of long-term fertilization on soil structure and organic carbon pools.A long-term wheat trial in Oklahoma was selected as the study object,including six fertilization treatments:CK-no fertilizer applied,M-only manure applied,P-only phosphate fertilizer applied,NP-applied both nitrogen and phosphate fertilizer,NPK-applied the combination of nitrogen,phosphate and potassium fertilizer,NPKL-applied nitrogen,phosphate and potassium fertilizer with lime.The responses of soil structure and soil organic carbon pools to fertilization were revealed by the study of organic carbon,total nitrogen and different forms of organic carbon in soil and soil aggregates under different fertilization conditions.The third part,the effect of different land use patterns on soil structure and soil organic carbon pools.Three long-term experiment site located in northern Louisiana were selected as the study object,including three soil type（clay,clay loam and silt loam）and three kinds of land use（crop rotation,energy crops and cottonwood）.The response of soil structure and different soil organic carbon pools to soil texture and cropping system were revealed by studying the organic carbon,total nitrogen and different forms of organic carbon in soil and soil aggregates under different soil texture and land use.The main results of the study are as follows:1.In the 7 different fertilization treatments（CK,U,CU,SASU,U+N,U+D）,the NH₃emission of each fertilization treatment was higher than that of non-fertilization treatment（CK）,and U treatment showed the maximum amount of NH₃ loss.Compared with U treatment,CU,U+N and U+D treatments significantly reduced the nitrogen loss in soil,and the EF values of NH₃-N were 0.41%,0.54%and 0.67%,respectively,which were lower than those of U,which were 49%,39%and 24%,respectively.The difference reached a significant level.Indicating that the polymer coated urea has the greatest inhibiting effect on ammonia volatilization in the soil,urea with urease inhibitors or nitrification inhibitors also have a certain inhibiting effect on ammonia volatilization,but the effect is not as good as the polymer coated urea.The ammonia volatilization from the SU and SASU treatments was lower than that of U treatment,but the difference was not significant.2.N₂O emissions from all fertilization treatments were higher than that of CK treatments.The emission amount from U and SU treatments are higher than that of other fertilization treatments.The main peaks of N₂O emission flux were 10 days later than that of NH₃,and its main peaks were closely related to soil and air temperature.The EF values of N₂O-N emission under U+N,CU,U+D and SASU were 0.12%,0.24%,0.28%and 0.80%,respectively,which were 87%,76%,69%and 20%less than that of U treatment,the difference reached a significant level.Indicating that nitrification inhibitors and urease inhibitors incorporated with urea and polymer-coated urea can effectively reduce soil N₂O emission.The daily average emission of CO₂ in all fertilization treatments were higher than that of CK treatment.The emission of CO₂ from soil was significantly correlated with soil and air temperature.The higher the temperature,the greater the emission amount.The application of fertilizers provides sufficient nutrients to the microorganisms and promotes root respiration of crops,which is the main reason of increased CO₂ emission occurred in fertilized soil.The emission of CH₄ in the soil fluctuated greatly during the wheat growing season,and nearly half of the results were negative,indicating that the dryland soil was generally appeared as the sink of CH₄.3.The long-term experiment of fertilization with different nutrient ratio and fertilizer ratio indicated that the application of chemical fertilizers or manure could increase the content of organic carbon in soil.Among all the fertilization treatments,the manure treatment（M）showed increased the most SOC content.Compared to the non-fertilization treatment（CK）,the organic carbon content in 0-15cm and 15-30cm soil layers under M increased by 50.47%and 21.02%,respectively,and the difference was significant.Indicating that the application of fertilizer has a greater impact on soil organic carbon content in the upper soil.All fertilization treatments increased the total nitrogen content in the soil,the largest increase appeared in M treatment,increased by 30.2%compared with CK treatment.The organic fertilizer treatment（M）increased the water-soluble carbon content（DOC）and the acid hydrolysable carbon content（HCl-C）in the 0-15cm soil layer by 93.12%and 46.72%,respectively.In the 15-30cm soil layer,the treatment of M and NPKL increased the DOC content by 44.87%and24.23%,respectively.The treatment of NPKL,M,NPK and NP significantly increased the content of HCl-C in 15-30cm soil layer.4.Compared with CK,organic manure treatment（M）significantly increased the>2000μm and 250-2000μm aggregate content in the 0-15cm soil layer,and the percentage of>2000μm aggregate increased from 0.27%（CK）to 2.31%（M）,and the percentages of 250-2000μm aggregates increased from 9.28%（CK）to 17.09%（M）.The increase from M treatment was higher than that of other fertilization treatments,indicating that the application of manure plays an important role in the formation of aggregates.The P treatment showed little effect on 53-250μm aggregates,but had a significant effect on>250μm aggregate in the15-30cm layer.Fertilizer application can significantly increase the mean weight diameter（MWD）of aggregates,and the order of MWD is M>NPKL>NPK>NP>P>CK.The contents of SOC,TN and HCl-C in different aggregates increased with the increase of particle size,and decreased with the deepening of soil layer.The effect of organic manure treatment on the contents of SOC,TN and HCl-C in soil aggregates was the most obvious.Among the inorganic fertilizer treatment,NP NPK and NPKL had greater effect on increasing soil nutrient content than P treatment.5.The contents of phenolic compounds,aromatic compounds and polysaccharides decreased with the decrease of aggregates size,while the N-containing compounds content increased with the decrease of aggregates size.Both organic and chemical fertilizers are beneficial to the increase of phenolic compounds,aromatic compounds,polysaccharides and N-containing compounds in soil aggregates.6.There is a big difference of the content of soil organic carbon and the proportion of liable carbon between different types of soils.The trend of the SOC content in 0-15cm soil layer was expressed as clay loam>clay>silty loam.The average SOC content in clay loam soil was 14.28%,which was 1.5 times higher than that of silty loam（9.54%）.DOC and HCl-C content in clay loam soil was 2.3 and 1.8 times higher than that of silt loam,respectively.The ratio of HCl-C content to SOC content in clay loam,clay and silt loam soil were 59.4%,50.5%and 52%,respectively.Indicating that the soil organic carbon in clay loam soil has the highest activity.In the 15-30cm soil layer,the order of SOC,DOC and HCl-C content in different soils was clay>clay loam>silt loam.However,in the ratio of HCl-C content to SOC content,the ratio reached 67%in clay loam,where clay and silt loam was 50%and 55%,respectively.Indicating that soil texture has a great impact on soil organic carbon activity.7.Different land use patterns have an important impact on soil organic carbon and its components.The order of SOC,TN and HCl-C content in the surface soil was cottonwood>croprotation>switchgrass,while the order of soil total nitrogen content was croprotation>cottonwood>switchgrass.Soil HCl-C content was strongly influenced by land use in different soils,and showed different extent of influence.In 0-15cm soil layer,the order of HCl-C content to SOC content ratio in 0-15cm soil layer of expressed as swithgrass>croprotation>cottonwood,,which was 63%,61%and 55%,respectively;expressed as cottonwood>swithgrass>croprotation in clay soil,which was 53%,51%and 48%,respectively;while expressed as croprotation>swithgrass>cottonwood in silt loam soil,which was 55%,51%and 50%,respectively.8.The distribution of aggregates in different soils was very different,the aggregates in clay and clay loam soils are dominated by>250μm size group,while the aggregates in the silt loam soil was mainly<250μm size.In 0-15 cm layer of clay loam soil,the>2000μm and250-2000μm aggregate content in the cottonwood treatment significantly increased compared to the croprotation treatment,with an increase range of 82.3%and 39.3%,respectively;while the increase range were 111.8%and 29.5%in 15-30cm layer,respectively.The 53-250μm aggregate proportion in the croprotation treatment increased,which was 1.32 and 1.12 times higher than that of the swithgrass and cottonwood treatments in the 0-15cm soil layer,respectively;while was 1.23 and 1.36 times higher in the 15-30cm soil layer,respectively.In general,large aggregates cotton in the cottonwood and swithgrass treatment were higher than that of croprotation treatments,while microaggregates were the highest in the croprotation treatment.9.The contents of organic carbon and total nitrogen in the aggregates were the highest in clay soil,followed by clay loam and silt loam soil.In the three soils,the organic carbon in different size of aggregates showed the same trend,the order was cottonwood>croprotation>switchgrass.The order of soil total nitrogen was croprotation>cottonwood>switchgrass.The SOC,TN and HCl-C content of aggregates increased with the increase of aggregate size.Although the organic carbon content of clay soil aggregates were the highest,the content of HCl-C in clay loam soil aggregate is higher than that of same size aggregate in clay soil in 0-15cm soil layer.In the same texture soil,the cottonwood treatment had the highest HCl-C content,followed by croprotation and switchgrass treatment.In general,urea incorporated with urease or nitrification inhibitor and polymer-coated urea can inhibit the emission of NH₃ and N₂O in soil.The application of organic manure and chemical fertilizers can promote the formation of large aggregates in the soil,and improve the content of organic carbon and liable organic carbon in different size aggregates.Compared with clay soil,the moderate clay content and large porosity of clay loam soil could be beneficial to the decomposition of organic matter by microorganisms,which may promote the formation of large aggregate;with less soil disturbance and richer plant residue input,the cottonwood treatment is conducive to the formation of large aggregates and organic carbon content in aggregates.