Effects of Soil Salinity Level and Nitrogen Rate on Urea-N Transformation in Grey Desert Soil

In order to valuate the transformation characteristic of urea-N in saline soil,a pot experiment was conduced to investigate the transformation of urea-N and soil enzyme activity under different soil salinity levels and urea application rates.The results showed that the transformation of urea-N in soil was influenced significantly by soil salinity and nitrogen rate.The NH4+-N content of soil increased with soil salinity level and urea application rate increased.The pH value and urease activity of soil were increased by urea application,and hydrolysis of urea was also promoted.The activity of urease was inhibited by soil salinity without urea application,but promoted by high soil salinity under urea fertilization.The nitrification was affected significantly by soil salinity,nitrogen rate,and their interaction.With soil salinity level and nitrogen rate increasing,the nitrification was inhibited intensely.Soil salinity had a slight effect on nitrate reductase activity,but the activity of nitrite reductase was depressed by soil salinity.These results suggested that ammonia volatilization loss could be aggravated in severe salinization soil when urea fertilizer was applied to excess,which can cause soil pH to increase.