[en] In field experiments on wheat from 1994 to 1998, grain yields and yield-contributing components increased with the amount of fertilizer N; however, differences with 120 and 180 kg N ha^-1 were not statistically significant. Grain yields ranged between 1.22 to 5.25 Mg ha^-1 over the four growing seasons. Water-use efficiency values increased with amount of fertilizer N applied. Total-N uptake was always highest with the 180 kg N ha^-1 treatment, i.e. with 50% more fertilizer applied than the locally recommended 120 kg N ha^-1. The use of ¹⁵N revealed that percent N derived from fertilizer from the first split application at planting, 40 or 60 kg N ha^-1, was lower than that applied as a second split of 80 and 120 kg N ha^-1, respectively, at growth stage Z-30; this trend prevailed in all the cropping seasons. Fertilizer-N uptake was highest with 180 kg N ha^-1 and varied from 16 to 50% of that applied. Nitrogen applied to the wheat had positive residual effects on subsequently grown rice in comparison with the zero-N checks. The downward flux of water measured in a nearby plot increased with depth, but showed a decreasing trend with wheat growth; the fertilizer-N fraction was relatively lower with depth. A minor fraction of applied N moved down to 120 cm, indicating little likelihood of pollution of groundwater by NO_3^- from fertilizer. (author)