Field experiments were conducted to investigate
ammonia volatilization from urea applied to green cabbage (Xiao Qing Cai)
in 2002 and Chinese cabbage in 2003 in the suburbs of Nanjing.
Ammonia volatilization was measured with the enclosure method.Results obtained were as follows: ammonia
Volatilization was low (<0 4%) after urea applied to the green cabbage due to the low pH value of the soil.In the Chinese cabbage field, of which the soil pH was 7 7, ammonia volatilization from the treatments of controlled release urea (N 180 kg hm -2 ), low rate N (300 kg hm -2 ) and high rate N (600 kg hm -2 ) as urea was 0 97%, 12 1% and 17 1%, respectively, of the total N applied.The results show that soil pH is an important factor affecting ammonia volatilization, reducing N application rate can reduce ammonia loss, and the use of controlled release urea is an effective way to reduce ammonia loss.Results of the experiment on timing of N application to Chinese cabbage show that rainfall following application of urea greatly affects ammonia volatilization because rain water reduces N concentration in the surface soil.The heavier and the closer the rain following the application, the less ammonia lost through volatilization.