Hf. Schnier, SIGNIFICANCE OF TIMING AND METHOD OF N FERTILIZER APPLICATION FOR THEN-USE EFFICIENCY IN FLOODED TROPICAL RICE, Fertilizer research, 42(1-3), 1995, pp. 129-138
N-use efficiency in flooded tropical rice is usually low. Fertilizer N
losses result mainly from losses of volatile NH3 after broadcast appl
ication of urea into floodwater between transplanting and early tiller
ing which is a common practice of farmers. Losses appear predominantly
during the first week after urea application. With broadcast and inco
rporation of N into soil at transplanting losses may be reduced but ar
e still substantial. Deep placement of urea supergranules (USG) has no
t been adopted by farmers because it is very laborious. A new applicat
ion technique, namely injection of dissolved urea into the upper soil
layer, was developed by which fertilizer N losses were effectively min
imized while at the same time allowing flexible timing of application
independent of crop stage and water management. It provides N-use effi
ciency equal to that achieved by USG point placement but is less labor
-intensive.