Study On Soil Ecological Stoichiometry Under Different Soil Management Practices In Dry Farmland Of The Loess Plateau Of Central Gansu Province

For researching the effects of different soil management practices on soil ecological stoichiometry in dry farmland.Three field experiments were conducted at the Rainfed Agricultural Experimental Station of Gansu Agricultural University,Dingxi,Gansu Province,China(35°28?N,104°44?E).The three separate field experiments were consisted of different tillage practices,nitrogen addition levels,and biochar addition levels.The tillage practices included the following treatments: conventional tillage with straw removed(T),no–till with straw removed(NT),no-till with straw mulch(NTS)and conventional tillage with straw incorporated(TS)arranged in a complete randomized block design with three replications.Nitrogen addition levels included the following treatments: N0(0 kg N·hm-2,no nitrogen addition),N52.5(52.5 kg N·hm-2,low nitrogen addition),N105(105 kg N·hm-2,appropriate nitrogen addition),N157.5(157.5 kg N·hm-2,high nitrogen addition)arranged in a complete randomized block design with three replications.Biochar addition levels included the following treatments: B0(0 t biochar·hm-2,no biochar),B10(10 t biochar·hm-2,minor biochar),B20(20 t biochar·hm-2,low biochar),B30(30 t biochar·hm-2,medium biochar),B40(40 t biochar·hm-2,high biochar),B50(50 t biochar·hm-2,very high biochar)arranged in a complete randomized block design with three replications.The soil samples were taken at four different soil depths(0-5 cm,5-10 cm,10-20 cm and 20-40 cm)per plot.The study was carried out to investigate the effects of different soil management practices on ecological stoichiometry of soil,microbial biomass and ecoenzyme activity and the influence factors,and to explore the optimum soil management practices for agricultural sustainable development.The study would provide theoretical basis for studying the carbon cycle of farmland ecosystem,and the balance and restriction of nitrogen and phosphorus elements for macroecology.The main results of the study are:1.The different soil management practices affected soil ecological stoichiometry characteristic in different ways.(1)Straw treated plots(S)significantly improved soil C:N,C:P,MBC:MBN and MBC:MBP,and ecoenzyme activity stoichiometry characteristic.(2)At 0-20 cm soil depth,soil C:N,and C:P were improved with increasing biochar addition.Addition of biochar improved MBC:MBN,MBC:MBP,MBN:MBP and ecoenzyme activity stoichiometry characteristic,and B30 level showed the highest effect.(3).Under nitrogen addition levels,addition of nitrogen had a significant decreasing effect on soil C:N;soil C:N was reduced with increasing nitrogen addition level.Addition of nitrogen improved soil C:P,N:P,and N105 level had the highest effect on soil C:P,MBC:MBN,MBC:MBP,and soil N:P was improved with increasing nitrogen addition level.Nitrogen addition had a decreasing effect on ?G:(NAG+LAP),?G:AP and increased(NAG+LAP):AP,and N105 level had the best effect.2.Ecological stoichiometry of microbial biomass and ecoenzyme activity showed different response degree on soil ecological stoichiometry.Under S and NS practices,ecological stoichiometry of microbial biomass and ecoenzyme activity adopted the “Constant proportional” model with changing of soil ecological stoichiometry without MBN:MBP under NS practice.Under biochar addition levels,MBC:MBN,MBN:MBP,?G:AP and(NAG+LAP):AP adopted the “Constant proportional” model with changing of soil ecological stoichiometry.MBC:MBP and ?G:(NAG+LAP)had constrain proportions by themselves,and impacted soil ecological stoichiometry.Under nitrogen addition level,MBC:MBN,?G:(NAG+LAP)and ?G:AP adopted the “Constant proportional” model with changes in soil ecological stoichiometry.MBC:MBP,MBN:MBP and(NAG+LAP):AP had constrain proportions by themselves,and impacted soil ecological stoichiometry.3.Soil available nutrients showed different response degree on soil ecological stoichiometry under different soil management practices.Under different tillage practices and biochar additional levels,soil available nutrients were improved with increasing soil C:N,C:P,MBC:MBN,MBC:MBP,MBN:MBP and ?G:(NAG+LAP),?G:AP,(NAG+LAP):AP.Soil available nutrients were decreased with increasing soil N:P.Under nitrogen addition levels,improved soil C:N,MBC:MBN,?G:(NAG+LAP),?G:AP can inhibit soil available nutrients,improved soil C:P,N:P and MBC:MBP,MBN:MBP,(NAG+LAP):AP can boost soil nutrition availability.4.Soil management practices can change the main control factors of soil ecological stoichiometry.(1)Uunder tillage practices,soil organic carbon(SOC)and soil total phosphorus(STP)were the main control factors of adjusting soil C:N,C:P and N:P,respectively.Mineral associated organic carbon(MOC)and STN were the main factors controlling MBC:MBN,MBC:MBP and MBN:MBP,respectively.SOC and STP were the main factors controlling ?G:(NAG+LAP),?G:AP and(NAG+LAP):AP,respectively.(2)Under biochar addition levels,soil organic carbon and soil total nitrogen were the main control factors of adjusting soil C:N,C:P and N:P,respectively.STN,STP,STN were the main factors controlling MBC:MBN,MBC:MBP,MBN:MBP,respectively.STN,STP,STN were the main factors controlling ?G:(NAG+LAP),?G:AP,(NAG+LAP):AP,respectively.(3)Under nitrogen addition levels,soil total nitrogen(STN),SOC was the main control factors of adjusting soil C:N,MBC:MBN,?G:(NAG+LAP),respectively.STN was the main control factors of adjusting C:P,N:P,MBC:MBP and MBN:MBP,(NAG+LAP):AP,respectively.STP was the main control factors of adjusting ?G:AP.In conclusion,farmland ecosystem had complicated and varied characteristics influenced by human factors.Different soil management practices showed different impact degrees on ecological stoichiometry of soil,microbial biomass and ecoenzyme activity in different ways.