Effects Of Biochar And Cotton Straw Application Rates On WUE And NUE In Cotton Under Drip Irrigation Conditions

[Object] Increasing soil organic carbon content, improving crop yields, and enhancing water and nitrogenuse efficiency are the important goal for optimal management of agriculture in arid region. Biochar is ahigh carbon content and stability of organic carbon, can effectively increase soil carbon storage, andimprove soil fertility and productivity. The influence of biaochar and cotton straw application rates ongrowth, yield, WUE, and NUE of cotton were evaluated under drip irrigattion conditions. The objective ofthis study is to promote the soil organic carbon storage, and to improve water and nitrogen use efficiency inarid region.[Method] Biochar was produced by cotton straw and prepared by pyrolysis at450°C high temperatureunder anaerobic conditions. The effects of biochar and cotton straw on soil organic carbon content, cottongrowth, water and nitrogen use efficiency under different nitrogen fertilizer application rates wereinvestigated with a field experiment. Three N levels were set as0,300, and450kg·hm^-2; representing N0,N300, and N450, respectively. The treatment of N300was equivalent to the recommended amount ofnitrogen fertilizer for local field. Under each N level treatment, the application rates of biochar and cottonstraw were three levels with equal organic carbon dosage as0,2.25, and4.50t·hm^-2. The application ratesof biochar were0,2.25, and4.50t·hm^-2（noted as CK,1/2BC and BC, respectively）. Three cottonapplication rates were0,6.0and12.0t·hm^-2（noted as CK,1/2ST and ST, respectively）. The split-plotdesign was used in this experiment, N level treatments were the main-plot, and the treatment of biochar andcotton application rates were sub-plot. There were15treatments and each treatment was repeated fourtimes with a total of60experimental plots.[Result]（1） The average water content in0-60cm soil depth under biochar and cotton straw treatmentswere15.3%and20.1%higher than that under CK, respectively. Soil respiration were increasedsignificantly by cotton straw added. Under N application rate at300kg·hm^-2conditions （N300）, the soilCO₂flux accumulation under ST and1/2ST treatments were10.8%and7.6%higher than that under CK,respectively; but the soil CO₂flux accumulation of BC and1/2BC treatments were reduced by7.3%and6.0%. The total N content in top soil were affected significantly by N, biochar, and cotton straw. Under N0conditions, the total N content of soil in ST and1/2ST treatments had26.4%and12.8%higher than CK,but there were no significant differences among BC,1/2BC, and CK treatments. Under N300conditions,the soil total N content of ST treatment was increased by25.9%, and no significant differences were foundbetween1/2ST and CK treatments. Compared with CK, soil total N in BC and1/2BC treatments increasedby32.3%and18.7%, respectively. Under N450Conditions, ST treatment had the highest soil total Ncontent, and then were BC and1/2ST treatments,1/2BC treatment had the similar soil total N content withCK.（2） The net N mineralization rate and nitrogen mineralization ratio of soil under cotton straw applicationtreatments were significantly higher than that under biochar treatments. Compared with CK, The net Nmineralization rate and nitrogen mineralization ratio of soil under ST and1/2ST treatments were increasedby150.6%,130.6%and117.2%,117.0%, respectively. BC and1/2BC were92.1%,64.3%and61.9%,49.2%higher than CK.（3） Cotton growth and yield were promoted by both biochar and cotton straw application. Under no Napplication conditions, the order of cotton yield were follow ST>BC>1/2BC>1/2ST>CK. Under Napplication rate at300kg·hm^-2conditions, the cotton yield for different treatments were ST>1/2BC、1/2ST>BC>CK. Under N application rate at300kg·hm^-2conditions, treatments of BC and ST had thehighest contton yield, and then was1/2BC treatment, treatments of1/2ST and CK had the lowest conttonyield.（4） The water and nitrogen use efficiency of cotton were increased significantly by biaochar and cottonstraw added. Under N application rate at300and450kg·hm^-2conditions, N uptake efficiency and apperant N recovery efficiency of cotton under biochar treatments （BC and1/2BC） were increased from27.4%to51.4%and14.9%to37.0%, respectively; while the cotton straw treatments （ST and1/2ST） only increasedfrom26.2to37.7%and5.4%to20.1%. the water use efficiency and irrigation water use efficiency undercotton straw treatments （ST and1/2ST） were increased from60.5to205.8%and from5.8%to39.3%, butbiochar treatments （BC and1/2BC） only increased from33.4%to159.8%and from13.2%to35.1%.[Conclusion] Therefore, the application of both biochar and cotton straw can improve soil organic carbonand total N content, increase cotton yield, and improve the efficiency of water and nitrogen use efficiency.To increase soil organic carbon and total nitrogen, reduce soil respiration, and improve nitrogen useefficiency, Biochar is better than cotton straw. Cotton straw can significantly promote soil nitrogenmineralization and soil respiration, increase cotton yield, and promote water use efficiency.