The aim of the study was to compare N uptake from initially-applied NH4+and NO3- ions and to compile a balance sheet for applied fertilizer N. In a pot experiment, maize, sorghum and sunflower plants were grown in succession, each for c. 6 weeks, to utilize the mineral N. The treatments were: NH4{NO3}, {NH4}NO3, {NH4}{NO3} and a zero N control, each replicated four times. The ions in brackets were labelled with15N, Although the applied ammonium nitrate was labelled in three different ways, the same quantity of N was applied initially and similar quantities of total N and soil N were together taken up by the three crops. The N recoveries from the two individual ions, however, differed. Results indicated that on average 75.8% of the initially-applied labelled NH4+-N was utilized by the vegetative tops of the three crops, this being significantly lower than the 85.9% of the labelled NO3-N utilized. The maize (1st) crop utilized 45.2%, the sorghum (2nd) crop 23.2% and the sunflower (3rd) crop 12.5% of the ammonium nitrate. When both NH4+and NO3- ions were labelled the N recovery corresponded with the sum of the findings where the ions were separately labelled. The accumulated N uptake by the successive crops from the soil reserves was higher where the soil was fertilized with ammonium nitrate when compared with the controls. The balance sheet took the N in the planted seed and the mineralization of soil N into account. It appeared that the addition of ammonium nitrate stimulated the mineralization of humus in the fertilized pots. The total soil analysis at the end of the experiment indicated that, on average, 17.7% of the fertilizer N remained in the pot soil. Eventually 100%, on average, of the applied ammonium nitrate could be accounted for in the N balance.