Abstract
Nitrogen trials were conducted using 15N-labeled urea and calcium ammonium nitrate in the production of maize (Zea mays L.) at three sites of contrasting agroecology in Nigeria. Split applications of banded, broadcast or point-placed N fertilizer had no consistent effect on grain yield or 15N uptake; however, at one N-responsive site, application of N in two splits significantly increased yield and grain 15N uptake over application of N in a single dose. 15N balances showed losses of 11-33% of applied fertilizer N. On the basis of N distribution in the soil profile, leaching was postulated to have been a problem at the wettest site, whereas ammonia volatilization appeared to have occurred at the less humid trials. 15N uptake by a cowpea (Vigna unguiculata (L.) Walp.) intercrop or relay crop was low in all trials.
