Bypass Flow Nitrogen Losses in Vertisols in Tropical Environments : Subtitle PREDISPOSING FACTORS FOR AMMONIUM- AND NITRATE-NITROGEN LOSS IN VERTISOLS IN THE TROPICAL ENVIRONMENTS

Bypass flow is one of the main avenues of fertilizer nitrogen (N) loss in agricultural fields. The magnitude of fertilizer N carried in bypass flow is influenced by soil characteristics, nitrogen species (i.e., NH4+ or NO3-) and rainfall patterns, inter alia. Wetting the soil prior to fertilizer application resulted in significantly (p ammonium sulphate > calcium nitrate, while the effect of N sources on nitrate-N were in the order calcium nitrate >urea = ammonium sulphate. The increase in nitrate-N in the effluent due to fertilizer rate were in the order 200 > 100 > 50 kg N ha-1. Ammonium- N losses were low being in the range 0.1 to 1 %, while nitrate-N losses were high, being in the range 0.02 to 21 % of the applied fertilizer.