Response Of Dry Farmland Soil Organic Carbon And Its Liable Organic Carbon Fractions To Nitrogen Fertilization In Loess Plateau Of Central Gansu Province

The paper based on the different nitrogen addition level tests in drought farm research Station in Gansu Agricultural University to explore the effects of soil organic carbon and its activated carbon components under N1(0 kg.hm^-2)?N2(52.5 kg.hm^-2)?N3(105 kg.hm^-2)?N4(157.5 kg.hm^-2)?N5(210 kg.hm^-2)these five nitrogen levels.The soil organic carbon and its activated carbon components were analyzed the effects of different nitrogen addition on the soil organic carbon and its composition of farmland during sowing and harvest in Longzhong Loess Plateau,revealed the effects of different nitrogen gradients on soil organic carbon and composition of farmland in Longzhong Loess Plateau.The conclusions are as follows:?1?When the nitrogen content was 105 kg.hm^-2,the soil organic carbon content was increased,and the order of the average content of soil organic carbon under different nitrogen application rates before sowing and after harvest was : N3 > N4 >N2 > N5 > N1;N3 > N4 > N1 > N2 > N5.?2?When the nitrogen content was 105 kg.hm^-2,the content of soil activated carbon was increased at two times.The order of average contents of ROOC?easily oxidized organic carbon?at two times was : N3 > N2 > N5 > N4 > N1.The order of average contents of HWOC?hot water extraction organic carbon?was: N3 > N2 >N1 > N4 > N5;N3 > N1 > N4 > N2 > N5,respectively.The order of average POC contents was : N3 > N2 > N4 > N5> N1;N3 > N2 = N4 > N5 > N1,respectively.The order of soil MOC?mineral-bound organic carbon?was : N3 > N2 > N4 > N1 > N5;N3 > N4 > N1 > N5 > N2,respectively.The order of average contents of soil SMBC?soil microbial biomass carbon?at two times was: N3 > N4 > N2 > N5 > N1.?3?The effect of different nitrogen addition on soil TN?total nitrogen?was less,and the average contents of total nitrogen in N2,N3,N4 and N5 treatments were higher than those in N1 treatment 5.70%,0.79%,13.34% and 13.29%;3.37%,4.49%,5.62%,7.78%.,respectively.?4?ROOC,HWOC,POC and SMBC are better than SOC to reflect the change ofsensitivity index,it meanings that ROOC,HWOC,POC and SMBC are also ideal indicators when evaluating the effect of different gradient nitrogen addition on the content of soil carbon change.There was a significant positive correlation between SOC and ROOC,HWOC,POC,MOC and SMBC in the three soil layers.In summary,the amount of nitrogen fertilizer was 105 kg.hm^-2,which was beneficial to the content of soil organic carbon.When the amount of nitrogen fertilizer was 105 kg.hm^-2,the contents of ROOC,HWOC,POC,MOC and SBMC were also improved,while the other nitrogen addition levels could decrease the contents of soil organic carbon and its activated carbon in different degrees.Therefore,when the amount of nitrogen fertilizer was 105 kg.hm^-2 could be used as reference nitrogen content in farmland soil of Loess Plateau in Longzhong.