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

Bok av Charles Onyango
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.