Emission Of Greenhouse Gases （CO₂&N₂O） And Wheat （Triticum Aestivum L.） Crop Productivity As Affected By Different Regimes Of Tillage, Nitrogen Fertilizer And Stubble Mulching In The Rainfed Environment Of Loess Plateau China

Escalating concentrations of different Greenhouse gases particularly the emissions ofCO2and N₂O are very hazardous for the environment. Rising concentrations of these gasesare not only detrimental for the healthy environment but are also injurious for thesustainability of whole production system. A2year study was designed to assess the effects ofdifferent tillage methods （Chisel plough tillage, Zero-tillage, Rotary tillage and Mouldboardplough tillage）, two mulch levels （M0i.e. No corn residue mulch and M1i.e. Corn residuemulch） and5N fertilizer levels （0,80,160,240and320kg N ha-1） on the emissions ofGreenhouse gases （CO2and N₂O） and wheat crop productivity under the rainfed ecology ofLoess Plateau China. Factorial experiment with three replications, having strip, split-splitarrangement, with tillage methods in the main plots, mulch levels in the sub-plots and N-fertilizer levels in the sub-sub plots was used for this study. CO2emissions data was recordedevery week by using the portable GXH-3010E1gas analyzer during the both years of study,while N₂O data was recorded from the Rotary tillage during wheat crop growing season2011-12. Data was also recorded regarding different soil properties like SOC, total soil Nitrogen,Soil enzymes, soil pH, soil moistures, soil temperatures, crop growth, crop photosynthesis,different environmental factors like air temperatures, relative humidity and wind speed etc.Data was also recorded regarding weeds infestations, fertilizer use efficiencies and economicsof production of wheat crop by using the different management practices.Maximum emissions of CO2were recorded in case of Rotary tillage planting method, ascompared to the minimum emissions of CO2recorded in case of Zero tillage planting method.In case of N fertilizer levels minimum emissions were CO2were recorded in case of160kg Nha-1, N fertilizer level. In case of different planting year’s maximum emissions of CO2wererecorded during the cropping year2010-11as compared to the year2011-12. During the cropping year2010-11, applications of corn residue mulch significantly increased theemissions of CO2as compared with the non residue mulched treatments, while during thecropping year,2011-12equal emissions were recorded in case of both kinds of mulchtreatments. Higher emissions of CO2were recorded immediately after the tillage operations.Different environmental factors i.e. rains, air temperatures, soil temperatures, soil moisturesand some soil characteristics like SOC, C/N ratio and soil enzymes like soil Urease and soilInvertase had significant effects on the emissions of CO2.The continuous use of N fertilizers for crops production is consistently increasing theemissions of N₂O in the atmosphere. One year （2011-12）, N₂O emission data was recordedfrom the Rotary tillage planting method. Two different mulch levels were applied includingapplication of no corn residue mulch and as well as application of corn residue mulch. Fivedifferent N fertilizer levels were used including, N0（0, kg N/ha）, N1（80kg N/ha）, N2（160kgN/ha）, N3（240kg N/ha） and N4（320kg N/ha）. Maximum emissions of N₂O were recordedduring the first three weeks of planting of wheat crop. Except in case of N3,（240kg N/ha） N,fertilizer level, applications of corn residue mulch reduced the emissions of N₂O in case of allthe other N fertilizer levels. On cumulative basis, minimum emission of N₂O was recorded incase of N1（8o kg N/ha）, N fertilizer level. Except in case of N3（240kg N/ha）, applications ofcorn residue mulch increased the grain yields in all the other N fertilizer treatments. So it canbe concluded that the application of crop residue mulch along with appropriate N fertilizerlevel has many environmental and economical benefits.Photosynthesis data was recorded on the different crop growth stages i.e. booting stage,50%heading stage, grain formation stage and near to crop maturity stage. Maximumphotosynthesis was recorded in case of Zero tillage planting method, followed by Chiselplough tillage method, while minimum photosynthesis was recorded in case of Rotary tillageand Mouldboard plough tillage method. Application of mulch improved the photosynthesisprocesses as compared to the non residue mulched treatments especially at the later cropgrowth stages. Similarly, as compared with the N0, N fertilizer level, application of higherlevels of N fertilizer, enhanced the photosynthesis up to a certain limit but further increase inthe rate of N fertilizer could not improve this processes. The results show that conservationtillage, use of mulches and application of appropriate N fertilizer can improve thephotosynthesis processes, which can be helpful in getting the better grain yields from the rainfed ecologiesRainfall timings and concentrations significantly affected the grain yields and water useefficiencies but on overall basis maximum water use efficiencies i.e.26.2kg/ha mm-1,51.5kg/ha and40.3kg/ha mm-1for grains, biomass and rainfall were recorded in case of Zero tillage planting method, followed by Chisel plough tillage. Equal water use efficiencies wererecorded in case of corn residue mulched or non mulched treatments. Although both yearsthere were variations in the water use efficiencies by using the different N fertilizers levels buton two years average basis application of80kg N/ha gave the maximum water useefficiencies. Data shows that the adaptation of Zero tillage technology is the most suitabletillage method to get the maximum water use efficiencies.Use of different tillage methods and application of corn residue mulch increased theSoil organic carbon （SOC） contents of the soil especially in the0-10cm soil depth, whichhelped in the reductions of the emissions of CO2. Variations in the rainfall timings andquantities resulted in the significant variations of grains yields during the different croppingyears. Variations in the grain yields due to the different management practices like use ofdifferent tillage methods and application of different N fertilizer levels significantly affectedthe wheat crop grain yields. Due to variations in rainfalls, during the cropping year,2010-11,maximum grain yields i.e.6.58t/ha and6.72t/ha were recorded in case of Zero tillageplanting method and similarly in case of80kg N/ha, N fertilizer level, while during thecropping year2011-12equal grain yields were recorded in case of all tillage methods,however maximum grain yield （7.46t/ha） was recorded in case of320kg N/ha, N fertilizerlevel. On two years average basis, maximum grain yields i.e.6.75t/ha and6.80t/ha wererecorded in case of Zero tillage planting method and similarly in case of80kg N/ha, Nfertilizer level as compared with the other tillage methods or N fertilizer levels. Use of cornresidue mulch reduced the weeds infestation up to40%as compared with the non residuemulched treatments. Economic analysis shows that the adaptation of Zero tillage plantingmethod and minimum use of N fertilizer according to the projected rainfalls, along with theapplication of corn residue mulch not only reduces the emissions of Greenhouse gases, butalong with improving the soil health, also reduces the use of herbicides.It can be concluded that the adaptation of Zero tillage, use of corn residues as a mulchand the application of minimum N fertilizers according to the projected rainfall are botheconomic and environmental friendly.