Using ¹⁵N Isotope To Reveal Nitrogen Distribution In Drip Irrigation Cotton Under Salt And Drought Stress

Object:Saline-alkali land in arid areas is an important land resource,and rational development and utilization can effectively promote economic and social development.The transport and transformation of nutrients under salt and drought stress have important effects on crop growth,crop yield and land use.Therefore,mastering the use of ¹⁵N isotope technology to reveal the nitrogen distribution and transformation of drip irrigation cotton under salt and drought stress is conducive to improving agricultural quality and efficiency,and is of great significance to cotton growth.Methrods:Using a two-factor three-level pit test,three soils with salinity gradients（conductivity,EC）were set up:3（T1）,6（T2）,and 9（T3）d S/m;three irrigation rates:2 700（W1）,3 600（W2）,4 500（W3）m³/hm²（4 500 m³/hm² is the local recommended irrigation amount）.The amount of nitrogen fertilizer applied was 300kg/hm².Cotton was selected from each test pit and wrapped with a ring,and an equal amount of ¹⁵N labeled nitrogen fertilizer was manually applied in its root zone.The HYDRUS model was used to study the water-salt migration law,and the DSSAT model was used to simulate cotton yield.Through the study of ¹⁵N absorption rate and ¹⁵N residual rate,the migration and accumulation law of nitrogen in crops was analyzed.Results:fter nitrogen utilization analysis and yield studies,increased soil salinity and drought inhibited cotton yield and growth.Conclusion:（1）The soil salinity increased obviously with the increase of depth,and decreased first and then increased with the growth period.Extreme water shortage is more likely to cause salt accumulation.Appropriate irrigation is beneficial to soil salt discharge.Water generally accumulates in the 20-40cm soil layer.（2）When the soil salinity gradient was greater than 3 d S/m,the soil total nitrogen and plant total nitrogen accumulation were significantly higher than those in the low-saline soil,and the soil salinity had a greater impact on the growth of cotton during flowering.The volatilized amount of ammonia nitrogen in the soil is proportional to the soil salinity gradient,and the leaching of soil nitrate nitrogen is proportional to the amount of irrigation water.Compared with the normal irrigation amount,the leaching of nitrate nitrogen in the soil increases with the increase of soil layer depth.8%speed reduction for soil layers.The accumulation of ammonia nitrogen in cotton plants is inversely proportional to the soil salinity gradient,and the accumulation of nitrate nitrogen in cotton plants is in direct proportion to the amount of irrigation.Water stress has a more serious impact on cotton yield.（3）The residual rate of ¹⁵ N in the soil of each treatment was 11%-40%,which increased with the increase of soil salinity and decreased with the increase of irrigation amount.;¹⁵ N residue rate was inversely proportional to cotton yield.The ¹⁵ N uptake rate of each treatment was 5%-58%,which decreased with the increase of soil salinity and increased with the increase of irrigation amount.The uptake rate of ¹⁵N was proportional to cotton yield.When the salinity is greater than 3d S/m,for every 50% increase in the salinity,the ¹⁵N residual rate increases by 19.5%,and the ¹⁵N absorption rate decreases by 9%.,¹⁵N absorption rate decreased by 18.4%.Moreover,the increase of salinity had a greater impact on the ¹⁵N absorption rate of fruit,and the decrease of irrigation amount had a greater impact on the ¹⁵N absorption rate of leaves and stems.（4）When the soil salinity gradient is greater than 6 d S/m,cotton yield decreases by 20%,and water stress causes cotton yield to decrease by about 5%compared with the normal value.Compared with 20%water shortage,soil salinity increases by 50%is more unfavorable.Increased cotton production.The maximum yield of T1W3 can reach 8000kg/hm²,and the nitrogen use efficiency is the highest,so the salinity is less than 3 d S/m,and the soil irrigation amount is 4500 m³/hm²,which is beneficial to the production and benefit of cotton.