Ammonia Volatilization From Rice Shoot Under Different Nitrogen Levels After Flowering

Close chamber method was used to study ammonia volatilization from rice shoot after flowering under different nitrogen levels.The correlation between the amount of ammonia volatilization and the nitrogen use efficiency was used for reference on properly applying nitrogen fertilizer,reducing nitrogen fertilizer loss,and improving the nitrogen use efficiency.The daily amount of ammonia volatilized from rice shoot was increased with the increase of nitrogen fertilizer application rate and came to a maximum within a few days after flowering,then decreased rapidly and was followed by relatively low amount for a long time.However,there was still a slight increase of daily amount of ammonia volatilized at milking and harvesting stages.The total amount of ammonia volatilized from rice shoot was also increased with the increase of nitrogen fertilizer application rate after flowering. The total amount of ammonia volatilization of Xidao 11 with low nitrogen use efficiency was much higher than that of Wujing 4 with high nitrogen use efficiency under the same nitrogen level.A significant variance of total amount of ammonia volatilization of Xidao 11 was observed under different nitrogen levels(F=75.09,P＜0.0001).Nitrogen harvest index(x₁,g·g^-1) and physiological nitrogen use efficiency(x₂,g·g^-1) was decreased with the increase of nitrogen fertilizer application rate.Both of NHI and PNUE were significantly negatively correlated with the total amount of ammonia volatilization from rice shoot after flowering(y,mg).The regression equations were list as follows:y=-0.02117 x₁+0.75186(R²=0.8426),y=-1.10386 x₂+35.52676(R²=0.8489). The ammonium concentration in leaf was high under high nitrogen level,which resulted in a high ammonia volatilization from rice shoot.Leaf GS activity and apoplastic NH₄⁺ concentration of rice plants were increased with the increase of nitrogen fertilizer application rate.Both of leaf GS activity and apoplastic NH₄⁺ concentration at anthesis were higher than those at harvest under the same nitrogen level.The amount of ammonia volatilization from rice shoot(y,mg) was significantly negatively correlated with leaf GS activity(x₁,μmol·g^-1·min^-1),and positively correlated with leaf apoplastic NH₄⁺ concentration(x₂,mmol·L^-1) at anthesis and harvest,y=-0.37846 x₁+0.41821 x₂+0.04925(R²=0.9471).Regression results showed that leaf GS activity and apoplastic NH₄⁺ concentration could affect ammonia volatilization from rice shoot significantly.The amount of ammonia volatilization from rice shoot and leaf GS activity were both increased with the increase of nitrogen fertilizer application rate,however,the amount of ammonia volatilization was significantly negatively correlated with leaf GS activity.This may be correlated with a process as follows:high leaf GS activity could facilitate much assimilation of ammonia in leaf,leading to a low ammonium concentration in leaf and low ammonia volatilization from leaf.