Wheat And Maize Straw Decomposition As Influenced By Different Nitrogen Sources, Zinc And Exogenous Microbial Compounds And The Effects On Soil Quality

Straw incorporation into cultivated fields has the potential to improve soil health andcrop yields. However, the presence of recalcitrant carbon compounds in straws remains aproblem worldwide. The addition of nitrogen fertilizer and exogenous microbial compound tohasten straw decomposition is being promoted in China to solve the problem and increaseacceptability by farmers. In this work, two series of laboratory incubation experiments wereused to investigate the potential of different mineral nitrogen sources and composite microbialcompounds on decomposition straw return directly to the soil and soil quality. In experimentone, the effect of different nitrogen sources with and without zinc on the rate of maize andwheat straw decomposition and soil quality was investigated. Soils were treated with threedifferent nitrogen sources: urea,（NH₄）₂SO₄, and NH₄Cl with and without zinc. Othertreatments were straw+zinc, straw+soil, and a no soil additive. Each pot containing150gsoil and1.125g straw with moisture content adjusted to80%of the field capacity wasincubated for53days at25°C. All results were significantly different at p <0.05with theexception of labile organic carbon （LOC）. Maize and wheat straw showed different patterns inCO₂evolution rates. For both straws, zinc had a synergic effect with urea, but an antagonisticwith the other nitrogen sources as determined by total CO₂production. Maize+urea+zinctreatment showed highest decomposition rate, while ammonium chloride （with or withoutzinc） had the least. The addition of NH₄Cl resulted in the highest total organic carbon （TOC）.Also, wheat straw decomposition induced higher microbial biomass accumulation comparedto maize straw.In experiment two, three types of industrially produced lignocellulolytic microbialcompound （Renyuan shengwu （RW）, Taigubio （TB） and China green health （GH）） andchemical nutrient （CN） formulated in the laboratory were investigated and compared to strawonly （WS） under two straw placement options （incorporation I and layered L）. The effect onwheat straw decomposition and soil biological and chemical properties were examined. Theresult indicated significant difference for all the parameters measured except soil NH4+N at p<0.05. The increase in soil-straw contact induced initial higher CO₂evolution in straw incorporated treatments compared to straw-soil layered pot but was not sustained to the end ofthe incubation. RW had highest total and cumulative CO₂emission follow by CN during the61days of incubation. Among the inoculants, only RW significantly increased CO₂over WS.There was positive correlation （R2=0.81） between total CO₂emission and cellulase activitywhile the relationship was negative between the total CO₂and dehydrogenase activity （R2=-0.66）. Placement option had effect on rate of CO₂evolution, total organic carbon （TOC）,microbial biomass carbon （MBC）, fungi and bacteria population and cellulase activity. Bothinoculation and straw returning to soil increased TOC, DTPA extractable Zn and Mn, total N,NO3--N, bacteria population and cellulase activity. RWL had highest MBC and bacteriapopulation while TBL had highest TOC. The results of these experiments demonstrated thatmineral nitrogen sources can affect ability of microorganisms to decompose straws and soilcarbon distribution. The straw placement method used in this research shows that increase inthe contact between soil and straw could induce higher initial decomposition rate. The directinoculation of straw return to the field could bring positive result on rate of strawdecomposition and soil chemical and biological properties if suitable microbial strains areused.