Effects Of Saline Water Irrigation On NH₃ Volatilization And N Use Efficiency In A Drip-Irrigated Cotton Field

[Objective] Ammonia volatilization is one of the main pathways of N loss from farmland soil.Saline water irrigation increased soil salinity in root zone, and it can have direct or indirect effects on soil NH₃ volatilization、N leaching and N uptake.The effects of saline water irrigation on soil physical, chemical and biological properties were investigated in this field experiment. The objectives of this experiment were（i） to learn more about the effects of saline irrigation water on the ammonia volatilization and N leahing,（ii） to determine the different water and nitrogen management on cotton N uptake, yield and ANR in saline water irrigation. To provide a theoretical foundation about the efficient use of water and nitrogen in saline water irrigation cotton field[Method] The experiment was conducted in 2014-2015.（1）The One field experiment about the effects drip-irrigated, saline irrigation water and N rate were determined using samples collected in 2014. The experiment consisted of a 3 × 4 factorial design with three levels of irrigation water salinity and four N rates. The water salinities were 0.35,4.61 and 8.04 d S m-1, representing fresh water（FW）, brackish water（BW）, and saline water（SW）,respectively. The four N rates were 0, 240, 360 and 480 kg ha-1（referred to as N0, N240, N360 and N480, respectively）.（2）The other field experiment about the effects drip-irrigated, saline irrigation water and irrigation amount were determined using samples collected in 2015. The experiment was designd with three levels of irrigation water salinity, two N rates and two irrigation amount.. The water salinities were 0.35, 4.61 and 8.04 d S m-1, representing fresh water（FW）, brackish water（BW）,and saline water（SW）, respectively. The two N rates were 0 and 360 kg ha-1（referred to as N0 and N360, respectively）. The two irrigation amount were 100%ETCand 75%ETC（ETCreferred to evapotranspiration for cotton crop）.[Result]（1） Saline water irrigation increased soil bulk density and soil salinity, but decreased soil macro-aggregate rate. Soil CEC, organic matter, total nitrogen and soil available N decreased as irrigation water salinity increased.There was no significance in available phosphorus and available potassium at the different treatment. Saline water irrigation decreased the microbal biomass carbon, biomass nitrogen and soil basal reapiration. Soi urease activity increased as the N application rates increased. saline water and brachish water irrigation was significantly increased urease activity.（2） The NH₄-N content increased as water salinity increased. However, NO₃-N content was exhibited the opposite trend. Soil NH₄-N and NO₃-N concentrations increased as the N application rates increased. Most of NH₄-N was being in the 0-40 cm depth. But most of NO₃-N was being in the 60-100 cm depth.（3）The amount of NH₄-N leaching, NO₃-N leaching and the proportions of applied N lost through leaching significantly increased as water salinity increased. N application increased the amounts of N leaching, but the ratios of applied N were not affected by N application rate. The amount of N leaching varied from 5.0 to 25.5 kg/ha, accounting for 1.81% to 4.79% of the urea-N applied under different water salinity and N application rate treatments（4） Soil NH₃ volatilization increased rapidly after urea fertigation, and peaked at 1-2 d after N application, then decreased rapidly. The amount of NH₃ volatilization varied from 9.0 to 33.7kg/ha, accounting for 3.2% to 3.8% of the N applied in all treatments. Soil NH₃ volatilization and N Leahing increased as irrigation water salinity, irrigation amount and N application rate increased. Soil NH₃ volatilization and N Leahing was significantly higher in the saline water treatment than that in either the fresh or the brackish water treatments. Soil NH₃ volatilization andN leahing in 100%ETc treatment was higher than 75%ETc treatment.（5） Cotton dry matter, N uptake and cotton yield decreased as irrigation water salinity increased. Nitrogen application rate increased nitrogen uptake and cotton yield. Cotton dry matter,N uptake and ANR in 100%ETc treatment were higher than 75%ETc treatment.[Conclusion]Saline water irrigation increased urease activity and soil NH₄-N content, but decreased NO₃-N content. NH₃ volatilization and N leahing increased as irrigation water salinity increased..Saline water irrigation decreased nitrogen uptake and ANR. Nitrogen fertilizer and irrigation amount significantly increased cotton growth, N uptake and cotton yield, But it was significantly increased soil NH₃ volatilization and N leahing. So, Increasing N application and irrigation amount increased risk of nitrogen loss in saline water irrigation...