Effect Of Nitrogen Fertilizing Rates And Sources On N Transformation And Ammonia Volatilization Of Paddy Soil In Cold Area

Urea is the main nitrogen source in rice production, and its conversion is directly related to the use and loss of nitrogen. The nitrogen absorption ability is limited in the early growth period duration of rice, which is easy to loss through various means. A laboratory study was conducted to study the transformation process of applied nitrogen fertilizer. Every chamber per treatment was sampled to determine the pH values in water and the ammonia volatilization loss at1,3,7,10,14and21days after N application, and to determine the NH4+-N and urea-N contents in water and different soil layers at3,10and21days after nitrogen fertilizer application. The objective of this study was to evaluate the effect of N rates and sources on nitrogen transformation and NH3losses.Results showed that urea could be sharply hypolyzed under urease, the NH4+content in the water layer increased, and the higher N application, the higher pH values, which aggravated the ammonia volatilization losses. The pH value in the water raised and reached the peak within the5-7days after urea applied. The pH peak value in Jian Sanjiang in the treatments with30,65and100kg N ha-1was7.38、7.50and7.66, respectively, and in Qing’an was6.76,7.00and7.27, respectively. The application of NBPT reduced the water pH value of0.15and0.26units on average, and prolonged the urea hydrolysis. The resin coated fertilizer ESN could inhibit and slow down the transformation from urea nitrogen, and controlled the water pH value effectively.Urea-N could be completed hydrolysis within the early3-10days after the application, and the ammonium nitrogen contents in the soil and water layers increased with the increase of the nitrogen fertilizer rates. The transformation of urea and its hydrolysis products were mainly concentrated in0-4cm soil layer, while muted impact on the other4-10cm layer. The ammonium nitrogen contents in water layer and the ammonia volatilization losses reached the peak within3to10days, and then gradually declined. During the cultivation, the ammonia volatilization losses in water layer on different days after fertilization in Qing’an are lower than that overall in Jian Sanjiang. The accumulated ammonia losses in the treatments of N applied in Jian Sanjiang and Qing’an were11.28-14.42%and3.39-7.96%, respectively. NBPT could inhibit the hydrolysis of urea to reduce the ammonium nitrogen in surface water and the ammonia volatilization peak, the accumulation of ammonia volatilization in Jian Sanjiang dropped from14.56to10.00kg N ha-1and the loss rate fell to10.00%from14.56%, the accumulation of ammonia volatilization in Qing’an decreased from6.14to0.62kg N ha-1and the loss rate fell to0.62%from6.14%. The application of resin coated fertilizer ESN, which reduced the ammonium nitrogen in surface water and the ammonia volatilization losses significantly as the slow release of nitrogen, and this was not relevant for the soil types.Total N recovery decreased with the addition of nitrogen application rates. The N recovery rates were75.71-86.37%in Jian Sanjiang and85.32-98.29%in Qing’an, respectively.15to20percents of N application disappeared without a trace because of the organic nitrogen and denitrified nitrogen did not be tested.