Effect of Different Soil Salinity Levels and Application Rates of Nitrogen on the Growth of Cotton under Drip Irrigation

The influence of different N fertilization rates and soil salinity levels on the growth and nitrogen uptake of cotton was evaluated with a pot experiment under greenhouse conditions.Cotton was grown in plastic containers(height 57cm,diameter 50cm) filled with a loamy soil.The experimental design was a 4×4 factorial with four salinity treatments(0.37,0.99,1.60 and 2.19dS m-1 as the electrical conductivity of 5:1 soil extract(EC)) and four levels of N(0,135,270,and 405kg N hm-2 as urea).Plant height was significantly affected by salinity and N-salinity interaction,but not by N.At low salinities,the plant height increased with increased N fertilization rates.At higher salinities,the plant height decreased with increased N fertilization rates.Seed cotton dry weight was significantly by salinity and N,but not by N-salinity interaction.Increased in salinity from 0.99 to 2.19dS m-1,dry weight of seed cotton was reduced by 52.33%,159.38%,and 864.63% respectively.Seed cotton dry weight increased with increased N from 0 to 270 kg hm-2,while further increase in N to 405kg hm-2 significantly reduced dry weight by 29.15% and 19.70%,respectively.Total dry biomass accumulation was significantly by salinity and N-salinity interaction,but not by N.Total dry biomass accumulation was significantly decreased with increased salinity from 0.37 to 2.19dS m-1 and increased with increased N from 0 to 135kg hm-2,while further increase of N application made no difference for total dry biomass accumulation.N uptake,which was significantly affected by salinity,N and N-salinity interaction,decreased with increase in salinity from 0.37 to 2.19dS m-1.This study indicates that the proper use of nitrogen fertilizer increased seed cotton and total dry matter weight of salt-stressed cotton.At low salinities,nitrogen content increased with increased N fertilization rates.At medium salinities,N uptake was enhanced when nitrogen properly fertilized,but not influenced by over-fertilization.At higher salinities,N uptake was independent of N rates and mainly influenced by soil salinity.