Effects Of Input Of Different Organic Materials On Co-transformation Of Carbon And Nitrogen And Environment In Farmland In North China Plain

China is a great agricultural country and abundant resources of farmland wastes such as livestock manure and straw were produced each year.It is an effective measure to dispose farmland wastes resources,improve soil fertility and crop yield using animal manure or returning straw to soil.The North China Plain is a major dryland grain production region in China.Studying livestock manure and straw returning to the field is of great significance to crop yield,soil fertility and risk of nitrogen loss in this area.Study on the characteristics of input of different organic materials on co-transformation of carbon and nitrogen and environment in farmland in North China Plain has become key issures.Considering a 27-year?1990-2016?long-term fertilizer experiment of Changping fluvo-aquic soil Eco-environment Key Field Scientific Observation Station of the Ministry of Agriculture and Rural Affairs as a platform,five fertilization treatments,including namely no nitrogen fertilzier?PK?,chemical fertilizers?NPK?,swine manure?NPKM,NPKM+?and straw incorporation?NPKS?,were selected.Each treatment has 200 m²?10 m×20 m?plot area.And then,crop yield of wheat and maize,soil carbon and nitrogen distribution characteristics of 0-200 cm profile,nitrogen leaching risk and N-related functional genes were analyzed.The main results obtained are as follows:1.Long-term additional application of manure and straw could increase crop yield.Compared with NPK,the yield of wheat and maize could increase by 31-37%,19%and 35%,21%under manure and straw returning,respectively,after 27 years.2.Long-term application of manure and straw returning could significantly improve soil organic carbon stocks.Soil organic carbon pool remained stable at 19.1-23.9 t C ha^-1 with 0.31 t ha^-11 year^-1 of exogenous carbon?NPK?supplemented annually.Soil organic carbon reached a stable level after 1.24 t ha^-11 year^-1 of exogenous carbon?NPKS?provided annually after 15 years,which stabilized at 20.5-26.1 t C ha^-1 with a growth rate of 1.8%.Interestingly,about 5.10-8.25 t ha^-11 year^-1 exogenous carbon was supplemented annually in NPKM and NPKM+treatments and resulted to an increase rate of 2.8-2.9%in the first 10 years and then increased to 4.7%-7.4%during 10-27 years.3.Long-term application of manure and straw returning could significantly improve soil nitrogen stocks.Soil nitrogen pool remained stable at 1.8-2.0 t N ha^-1 with 338 kg ha^-11 year^-11 of exogenous nitrogen?NPK?supplemented annually.Soil nitrogen reached a stable level after 372.1 kg ha^-11 year^-1 of exogenous nitrogen?NPKS?provided annually after 15 years,which stabilized at 2.1-2.3 t N ha^-1 with a growth rate of 0.04%.Interestingly,about 586.3 kg-707.5 kg ha^-11 year^-11 exogenous nitrogen was supplemented annually in NPKM and NPKM+treatments and resulted to an increase rate of 2.3%in the first 15 years and then increased to 4.1%-4.9%during 15-27 years.4.Long-term additional application of manure increased the risk of soil nitrogen leaching,and straw returning could enhance soil nitrogen retention ability.The input amount of total nitrogen in manure treatment was 1.7-2.1 times that in chemical fertilizer treatment.Nitrate nitrogen?NO₃^--N?content in0-200 cm profile of NPKM and NPKM+treatment was 7.6-8.4 times that of NPK(67.6 kg N ha^-1),and apparent balanced nitrogen surplus was 1.4-2.5 times that of NPK treatment.It indicated that additional application of manure would increase the risk of soil nitrogen leaching.It was related to the large amount of nitrogen by organic manure itself.The correlation analysis between the abundance of functional genes related to nitrogen cycle and long-term fertilization showed that compared with NPK,long-term additional application of manure significantly increased the abundance of ammonia-oxidizing bacteria?AOB?and soil nitrification rate?r=0.66,P<0.05?.It suggested that the increased risk of soil nitrogen leaching was mainly attributed to the increased activity of AOB and soil nitrification rate.Although the content of NO₃^--N in 0-200 cm profile of NPKS treatment increased slightly compared with NPK treatment,the surplus of soil nitrogen decreased significantly?39%?.Especially the higher negative nitrogen mineralization rate?3.4-15 times?in deep soil?120-200 cm?,suggesting that straw returning to field contributed to the enhancement of soil nitrogen retention ability.In conclusion,applying organic manure and straw incorporation on the basis of chemical nitrogen fertilizer can increase crop yield and stocks of soil carbon and nitrogen of wheat-maize rotation in North China Plain.However,the level of manure fertilization as much higher and resulted accumulation of nitrate nitrogen seriously and might threaten the safety of groundwater.