Maize Yield And Quality Response To Soil Amendment And Tillage Practices And The Underlying Mechanisms In The Semi-arid Loess Plateau

China‘s demand for maize is increasing at a robust pace,driven mainly by growth in the livestock industry.Increasing maize yield and quality is a critical factor in determining China‘s ability to meet its growing demand for maize with domestic production.Agronomic practices such as soil amendment and tillage practices play a significant role in increasing maize yield and quality;however,these practices could lead to increased CO₂ emission.Increasing and sustaining maize production and quality without a compromise on environmental integrity has become very necessary.This study is to optimize soil amendment and tillage practices for improved maize yield and quality and ensures environmental sustainability,and also explores the underlying mechanisms in the semi-arid Loess Plateau.Based on this,three experiments?i.e.,nitrogen rate and time of application,soil amendment and tillage practices?were conducted at the Rainfed Experimental Station of Gansu Agricultural University,located in Anding district,Dingxi,Gansu Province,China.The experiment on nitrogen was a split plot with eight treatments.Main treatments were: 0 kg N ha^-1?N₀?,100 kg N ha^-1(N₁₀₀),200 kg N ha^-1(N₂₀₀),300 kg N ha^-1(N₃₀₀)and sub treatments were: ? N application at sowing and ? at pre–flowering?T1?,? at application at sowing,? at pre–flowering and ? at milking?T2?.The experiment on soil amendment utilized the following treatments: no amendment?NA?,swine manure?SM?,maize stover?MS?,and swine manure in combination with chemical fertilizer?SC?.The experiment on tillage practices utilized 4 treatments: conventional tillage?CT?,rotary tillage?RT?,sub-soiling?SS?and no-till?NT?.All the three field experiments were initiated in 2012;however,this thesis reports the experimental data for the 2014,2015 and 2016 cropping seasons.Main findings are summarized as follows:?1?.Nitrogen application at N₃₀₀ increased grain yield by 79 and 56% compared to N₀?not fertilized throughout the experimental period?and N₁₀₀ respectively.Application of T1 increased grain yield by 8% compared to T2.Among amendment treatments,SC increased grain and forage yield by 69 and 59% compared to NA.Subsoiling?SS?increased grain and forage yield by 20 and 24% compared to CT.Generally,N₃₀₀ applied ? at sowing and ? at pre–flowering,swine manure in combination with chemical fertilizer and subsoiling greatly increased grain and forage yield.?2?.Crude protein?CP%?decreased with plant maturity whereas acid detergent fiber?ADF?and neutral detergent fiber?NDF?increased with maturity.The increased ADF and NDF with maturity resulted to decreased relative feed value?RFV?irrespective of treatment.Application of N₃₀₀ increased CP% across growth stages by 42,19 and 3% on average compared with N₀,N₁₀₀ and N₂₀₀,respectively.ADF and NDF was decreased by nitrogen application(N₁₀₀,N₂₀₀ and N₃₀₀)compared with N₀.Amendment treatments recorded lower ADF,NDF and greater CP%,RFV compared with NA.SC increased CP% by 6% compared with SM and MS.Tillage practices recorded non-significant differences in CP%,ADF,NDF and RFV.Nitrogen at 300 kg ha^-1 and swine manure in combination with chemical fertilizer improved maize quality,however,tillage had no significant effect on quality.?3?.Application of N₃₀₀ recorded significantly higher(1048 Kg ha^-1)carbon emission?CE?,however,higher grain yield under N₃₀₀ increased carbon emission efficiency?CEE?by 53% compared with N₀.The effect of SC on CEE was similar to N₃₀₀.Subsoiling?SS?,NT and RT reduced CE and increased grain yield,resulting to 54,33 and 12% increased CEE,respectively,compared to CT.Water consumption?ET?was relatively higher in high-yielding treatments,but it also increased grain and biomass yields,resulting to higher grain water use efficiency?WUEg?and biomass water use efficiency?WUEb?,respectively.Nitrogen at 300 kg ha^-1,swine manure in combination with chemical fertilizer and subsoiling increased grain and biomass water use efficiency.?4?.Nitrogen rate and time,soil amendment and tillage practices influenced soil water content?SWC?.Average soil water content in the 0-110 cm depth was highest in N₃₀₀.However,SWC was significantly lower?0-30 cm depth?in the N₃₀₀ treatments at 120 DAS?milking?and 153 DAS?maturity?of maize compared with N₀.Under soil amendment,SC recorded higher SWC?0-110 cm depth?followed by SM and the least in NA.No amendment increased SWC at 90 and 120 DAS compared with amended treatments in the 0-30 cm depth.Subsoiling?SS?recorded the highest SWC?0-110 cm depth?,followed by NT,RT and CT.Subsoiling?SS?significantly decreased soil bulk density??b??9%?,increased soil hydraulic conductivity?Ksat??23%?,water filled pore space?WFPS??14%?and mean weight diameter?MWD??31%?compared to CT.Nitrogen at 300 kg ha^-1,swine manure in combination with chemical fertilizer and subsoiling increased soil water content?0-110 cm depth?.?5?.Nitrogen application at 300 kg ha^-1(N₃₀₀)increased leaf area index?LAI?,chlorophyll content,leaf water potential,stomata conductance?gs???59%?,net photosynthesis?PN??80%),and transpiration rate?E??85%?compared to N₀.Application of T1 increased gs,PN and E by 15,19,and 13%,respectively,compared with T2.Swine manure in combination with chemical fertilizer significantly increased LAI?33%?,chlorophyll content?12%?,and leaf water potential?17%?compared to NA.The SS increased photosynthetic activities compared with CT.The increased SWC under N₃₀₀,swine manure in combination with chemical fertilizer and subsoiling increased LAI,chlorophyll content,leaf water potential and photosynthetic activities.?6?.Soil water content highly and positively correlated with gs,PN,E,grain yield,forage yield and WUEg,signifying that the increased soil water content increased photosynthetic activities,and thus increased grain and forage yield.In conclusion,nitrogen at 300 kg ha^-1,swine manure in combination with chemical fertilizer increased maize yield and quality,and water use efficiency due to increased soil water content and thus improved crop physiological index.Crude protein and relative feed value were increased whiles acid detergent and neutral detergent fibers were decreased under these treatments.Subsoiling increased grain yield and water use efficiency however,tillage practices generally had no significant effect on maize quality.Nitrogen at 300 kg ha^-1 and swine manure in combination with chemical fertilizer increased soil carbon emission but enhanced carbon emission efficiency through increased grain yield.Subsoiling increased carbon emission efficiency through reduced carbon emission and increased grain yield.Application of N at 300 kg ha^-1,swine manure in combination with chemical fertilizer and subsoiling appears to be the optimum soil amendment and tillage practices to improve yield and quality of grain and forage maize,and improve carbon emission efficiency in semiarid Loess Plateau.