The Distribution Of Labile Organic Carbon Along The Soil Profile And Its Driving Factors In Upland Soils Subjected To Long-term Fertilization

Due to its high sensitivity,soil active organic carbon(Labile SOC)can be used as an early indicator of soil organic carbon change caused by soil management measures such as fertilization.In this study,the distribution characteristics of labile organic carbon components in soil profile of different types of soil under long-term fertilization conditions are still unclear,and the main controlling factors are still unclear.Three long-term test sites for fertilizers distributed in different soil types in China are selected.(Jilin Gongzhuling Black Soil,Henan Zhengzhou fluvo-aquic soil,Hunan Qiyang Red Soil),four fertilization treatments selected included cropping without fertilization(CK),inorganic fertilizer nitrogen,phosphorus and potassium(NPK),inorganic fertilizer with manure(NPKM)and inorganic fertilizer with straw(NPKS).The soil sample of 0-100 cm was collected,and the difference characteristics of labile carbon storage in farmland soils were evaluated by the content and proportion of labile organic carbon in different components,and the stability and turnover rate were further evaluated.Six carbon sugar/five carbon was utilized.The ratio of sugar to evaluate the dominant role of plant and microbial carbohydrates in soil labile carbon pool;by measuring soil properties and meteorological factors,using CCA-VPA multivariate statistical method to determine carbon pool activity,carbon efficiency and soil activity the driving mechanism of carbon pool conversion.The Results showed that:(1)The SOC storage in 0-20 cm soil layer increased highest in NPKM(100%,115% and 94%)treatment while lowest in NPK(15%,43% and 40%)treatment relative to CK in ZZ,QY and GZL sites respectively but sharply decreased with increasing soil depth in each site.The NPKM,NPKS and NPK treatment increased the SOC storage in whole soil profile by 55%,39% and 6.0% in ZZ,91%,64% and 42% in QY and 26%,64% and 28.0% in GZL site.In whole profile the same treatment(NPKM)had highest SOC storage as compared to control in each site(2)The long-term fertilization also increased labile SOC storage pool in 0-20 cm soil layer,but declined sharply with the increasing soil depth at each experimental site.The average SOC storage of total,less,mid and highly labile fraction in manure with balanced fertilizer(NPKM)at 0-40 cm depth of GZL increased 113%,46%,139% and 275% and were determined higher by 112-91%,142-26%,190-204% and 90.0-130% respectively,as compared to CK in 0-100 cm of ZZ and QY site.Besides,the proportions of all the labile fractions in SOC were highest in the NPKM treatment,(9-44% in GZL,14.0-50.0% in ZZ and 13-56% in QY)and the lowest in the control(5-35% in GZL,8.0-38.0% in ZZ and 8-47% in QY sites).Comparison to sites SOC and labile storage was highly recorded in NPKM treatment of GZL(50.0-20.0 Mg ha-1)site compared to ZZ(30.0-14.0 Mg ha-1)and QY(36.0-16.0 Mg ha-1)site in surface soil(0-20 cm).(3)The greatest accumulation of neutral sugar(glucose,galactose and muramic)was observed in balanced fertilizer(NPK),compared to integrated manure with balanced fertilizer(NPKM)treatment and integrated straw with inorganic fertilizer(NPKS)in 0-20 cm.Control plot showed the lowest value in 0-20 cm.The highest accumulation observed in glucose amine followed by galactose amine and muramic acid.The plant-derived ratio of glucosamine and Muramic acid(GulN:MurA)amino sugar enriched in surface soil then other soil layers and ratio was observed highest in manure with inorganic fertilizer(NPKM)treatment compared to control.(4)Soil properties,exogenous carbon input and climate can explain 60.7%(P<0.05)variation of different organic carbon components,the three explained 56.0%(P<0.05),48.1%(P<0.05)and 27.4%(P<0.05),respectively.The root carbon and soil microbial biomass carbon classes explained 33.1% and 21.8%,respectively.The results of this study indicate that NPKM can increase the content of active organic carbon in different dry land soils in China.At the same time,soil properties,exogenous organic carbon input and climate are the main factors affecting soil labile carbon storage.The research results will deepen the understanding of the carbon conversion mechanism of farmland system and provide a scientific basis for the efficient improvement of soil organic carbon in dry land in typical regions of China.