The Impacts Of Swine Manure Treatments And Application Years On Soil Nitrogen Flux

The various treatments of swine manure lead to the differences in its forms,nutrient contents and nitrogen（N）availability.There is still lack of systematic evaluation for the dynamic changes of N under the storage and field application of swine manure at present.In addition,although there are numbers of studies on the long-term application of swine manure,it is also not clear that the impact of swine manure application years on soil N flux,soil carbon（C）and N stocks.The current study focuses on four forms of swine manure including:raw slurry（RS）,liquid fraction of solid-liquid separation（LF）,solid fraction of solid-liquid separation（SF）and dried manure（DM）were selected to analyze the dynamic change in manure N contents under storage and field application.In order to reveal the effects of swine manure application on soil N fluxes and soil carbon and N stocks,a short-term（from 2016 to 2017）and a long-term（from 1990 to 2017）experiment was examined,which includes treatments as:no fertilizer（CK）,chemical N,P,K fertilizers（NPK）,chemical N,P,K fertilizers plus 22.5 t/ha proper swine manure application（NPKM）,chemical N,P,K fertilizers plus 33.7 t/ha excessive swine manure application（NPKM+）.The observed results are as follows:（1）In the process of storage and field application for different kinds of swine manure,the nitrogen loss by SF fraction was low as compared to other fractions.The ammonia（NH₃）volatilization and TN loss was minimum（2.7%and 5.4%）during the SF storage.In the LF storage process,the NH₃volatilization loss was maximum,which was up to 9.9%.For RS,the TN loss was the maximum,which was 26.4%.Significant difference was measured in NH₃ volatilization loss under the swine manure application of different forms,the NH₃ emission factor for SF（3.3%）was the lowest,which was only34.0%of LF（9.7%）treatment.The greenhouse gas emission intensity（GHGI）for SF was only 0.13 kg CO₂-eq/kg yield,which was significant lower than RS and DM treatment,respectively.（2）The study on short-term swine manure application showed that,swine manure application had a positive effect on the increase of wheat yield and the improve of soil carbon and nitrogen stocks,and also had a positive effect on the reduction of ammonia emission factor,but it would increase GHGI;however,the excessive application of swine manure could decrease the positive effect on the increase of wheat yield,and significantly increase the GHGI.Compared with NPK treatment,the wheat yield in NPKM and NPKM+treatment increased from 6098 kg/ha to 6887 and 6325 kg/ha;the soil（0-20 cm）organic carbon stock（SOC）increased from 56.1 t/ha to 58.5 and 63.3 t/ha;the soil nitrogen stock increased from 3.1 t/ha to 3.7 and 4.4 t/ha;the soil NH₃ emission factor decreased from 2.2%to 1.1%and 1.3%.Compared with NPK treatment,the GHGI for NPKM and NPKM+was increased by 5.5%and 35.0%,respectively.（3）The study on long-term swine manure application showed that,the application of swine manure had a positive effect on the increase of wheat yield and the improvement of soil carbon and nitrogen stocks,and also had a positive effect on reduction of ammonia emission factor and GHGI.However,the excessive application of swine manure,decreased the positive effect on the increase of wheat yield,meanwhile increased the GHGI.Compared with NPK treatment,the wheat yield in NPKM and NPKM+treatment increased from 3880 kg/ha to 7105 and 5625 kg/ha;the SOC stock（0-20 cm）increased from37.0 t/ha to 65.7 and 70.6 t/ha;soil nitrogen stock increased from 3.6 t/ha to 6.5 and 7.9 t/ha;the soil NH₃ emission factor,decreased from 2.2%to 1.1%,respectively.It was noteworthy that,compared with NPK treatment,NPKM could decrease GHGI by 18.0%,while NPKM+increased GHGI by 21.2%.In summary,the solid fraction of swine manure solid-liquid separation could effectively reduce the risk of N loss and improve the N utilization efficiency,which is the best mode of swine manure disposal and application.The proper swine manure application not only significantly improved soil carbon and nitrogen stocks,but also significantly reduced the emission factor of ammonia and greenhouse gas emission intensity.What’s more,the long-term proper swine manure application could strengthen the positive effect.Therefore,it is suggested that the swine manure can be applied for a long-term in areas where soil nutrients are relatively lower.