| Objective:soil salinization is one of the important factors restricting the sustainable development of agriculture,and saline soil is a very important reserve cultivated land resource in our country.As a pioneer crop of salinized farmland,cotton is of great significance to adapt to or control soil salinization,but under the background of complex and changeable temporal and spatial distribution of saline soil,its physiological growth and nitrogen absorption and utilization response to different gradients of soil salinity is still not very clear.Methods:the experiment of drip irrigation under plastic film was carried out during the growth period of cotton from 2019 to 2020.Different gradients of soil salinity and irrigation nitrogen application were set up(low salt S1=7.7 ds·m-1,medium salt S2=12.5 ds·m-1,low water I1=289.42 mm,middle water I2=387.56mm,high water I3=480.7 mm,low nitrogen N1=206 kg·ha-1,medium nitrogen N2=275 kg·ha-1,High nitrogen N3=343 kg·ha-1).Results:based on the multi-interdisciplinary knowledge of soil physics,plant physiology and agronomy,the mathematical statistical methods such as analysis of variance,correlation analysis,principal component analysis,multi-objective optimization and spatial analysis were comprehensively used to carry out the effects of the interaction of water,salt and nitrogen on physiological growth indexes such as cotton root growth and nitrogen absorption and utilization,and put forward the ideal water and nitrogen production model of soil salinity cotton field with different gradients.The main results are as follows:（1）The interaction effects of water,nitrogen and salt on root morphology（root surface area,root volume and root diameter）were significant at bud stage,boll filling stage and boll opening stage.Under S1salinity gradient,the responses of root morphology indexes to nitrogen application were different under different irrigation levels.The root surface area and root volume of I1 and I2 decreased with the increase of nitrogen application rate.Under S2 salinity gradient,there was no significant difference between I1N1 and I1N2 treatments,and the root surface area under I2 irrigation level increased by 16.73%and 9%compared with I1 and I3,respectively.There was no significant difference in root surface area under different salinity gradients,and the maximum value of root length density（RLD）was distributed in 20-30 cm shallow soil.Under S1 salinity gradient,the average rld of I1 and I3 treatments with different nitrogen application levels were 7.3%and 3.3%lower than that of I2 treatment,respectively;the root length density increased first and then decreased with the increase of nitrogen application rate;increasing nitrogen application could significantly increase the root weight density of cotton.（2）The interaction of water and nitrogen had significant effects on total nitrogen uptake,total soil nitrogen uptake and nitrogen use efficiency（NUE）of cotton（P<0.01）,but the partial productivity of nitrogen fertilizer（PNP）had no significant effect（P>0.05）.The results showed that the average total nitrogen content of cotton was N2>N1>N3 under different nitrogen application treatments on S1 salt gradient;the total nitrogen content of cotton organs before boll stage was leaf>bud>stem>root;after boll stage,it was boll>leaf>stem>root;the total nitrogen content of cotton leaves,buds,stems and roots was S1>S2 under two kinds of salt;the total nitrogen absorption of cotton was 1.38-3.02 g/plan.The results showed that the total absorption of urea nitrogen was 0.20-0.55 g/plant,the total absorption of soil nitrogen was 1.71-2.47 g/plant,nue was 18.0-37.76%,and PNP was 13.92-27.08 kg·kg-1.（3）Irrigation had significant effects on Lai,boll weight,dry matter quality and yield.With the increase of salinity,water and nitrogen use efficiency decreased significantly.Under S1 and S2 salt gradients,the water and nitrogen use efficiency of I2N2 treatment was higher than that of other water and nitrogen treatments.The yield of I2N2 treatment was higher than that of other treatments in two kinds of saline soil.The economic benefits of S1 salt gradient I2 were 1.78-3.45 and 1.18-1.53 times of I1 and I3,respectively.The economic benefit of S2 salt gradient I2 was 2.93-4.44 times of I1.Using multiple regression and spatial analysis,the irrigation and nitrogen application ranges of cotton yield,economic benefit,water use efficiency,nitrogen use efficiency and nitrogen partial productivity reached 85%of the maximum value under two salt levels:the irrigation amount was 379.18-383.09 mm,351.24-370.45 mm,and the nitrogen application rates were 256.69-315.45 kg·ha-1and 221.36-282.85 kg·ha-1,respectively.（4）The first principal component of S1（S1PC1）could explain 63.93%of the total variation,and was positively correlated with yield,WUE,NUE,RLD,RMD,RSA,RV and Rd.18.33%of the variation explained by S1 second principal component（S1PC2）was positively correlated with WUE,NUE and RV.The first principal component of S2（S2PC1）could explain 59.4%of the total variance,and was positively correlated with yield,NUE,RLD,RMD,RSA,RV and RD.The research results can preliminarily reveal the response mechanism of cotton root distribution to soil salinity in different gradients,and provide a scientific theoretical reference for improving water and nitrogen use efficiency and adapting to the management of salinized farmland in the arid and semi-arid areas of Northwest China. |
PDF Full Text Request