尿素施入稻田后氨挥发损失的估测

Estimates of Ammonia Volatilization Losses from Applied Urea in a Wetland Rice Field

小试验估测的在菲律宾热带气候条件下尿素表施或混施入稻田后的氨挥发损失率为10%上下。尿素在无渍水存在时进行混施能在一定程度上减少其氨挥发损失。同时测定的稻田水层氮含量和pH 值结果表明,通常的施肥方法无法避免施入稻田的大部分肥料氮溶解在水中,稻田水层的 pH 值受水中生物(主要是藻类)活动的影响,日间可上升到9以上。因此,即使在酸性土壤上,氨挥发在稻田氮素损失中的意义,也是不能忽视的。

A simple acid trap unit(Fig.1)was used to measure directly the ammonia volatilization losses from applied urea under farmer's wetland rice field conditions in Philippines.The deep-placed supergranules of urea gave the lowest ammonia losses.The incorporated prilled urea gave lower magnitude of ammonia volatilization losses in the wetland rice field without floodwater as compared to that with floodwater(Tab.1).From the urea topdressed at different stages of rice growth,the losses by ammonia volatilization,on average,ammounted to 11.9% of N apnlied(Tab.2). Total N(urea-NNH_4^+ -N),pH and temperature in floodwater were simultaneously tested for 10 days after fertilization in the wetland rice field.It was found that the applied urea resulted in a elevated N level in the floodwater which declined to rapidly negligible level within 3-6 days(Fig.2).Rather strong alkaline reaction in floodwater(pH>8)was often recorded(Fig.3)indicating that there was really a significant potential for ammonia volatili- zation in the wetland rice field,though the soil(pH 6.0)and the irrigation water(pH 6.5) both were slight acidic.