NITROGEN LOSSES BY VOLATILIZATION IN A CORN CROP WITH 2 TILLAGE SYSTEMS IN THE ARGENTINE PAMPA

Ammonia volatilization from soils is a complex process generally assoc iated with surface applied nitrogen (N) fertilizer. The effect of conv entional tillage and no tillage on NH, volatilization was evaluated on cultivated corn (Zea maize L.) field in Pampa Humeda, Argentina. The objectives of this study were a) to determine the amount of N loss by volatilization (NH3) from urea fertilized soils under two different ti llage systems (conventional and no tillage) and two different fertiliz er application methods (surface and incorporated application) and b) t o relate volatilization losses with environmental factors and biochemi cal and microbiological properties. This experiment was conducted on a Vertic Argiudoll with a silty clay loam texture in the Argentine Pamp a. The site has been in natural grassland for 8 years prior was plante d to corn. Following the fertilizer application for conventional tilla ge and no tillage systems, the daily volatilization loss of NH3 on the fertilized plots was highest during the first three days. Higher loss es of NH3, occurred in the no-tillage treatments, with 11.5% and 6.2% of N-urea lost when the fertilizer was surface applied and incorporate d, respectively. For conventional tillage, 8.6 % of the N was lost whe n the fertilizer was surface applied and 5.4% when the fertilizer was incorporated. Surface application of urea stimulated urease enzyme act ivity. An opposite effect was observed when the urea was incorporated. Environmental changes conditioned the availability of energy substrat es for microorganisms, which resulted in different rates of intensity of biochemical reactions in the soil. Multiple regression equations sh owed differences between surface applied urea and incorporated urea tr eatments due to the latter avoiding the direct exposure of the fertili zer to atmospheric conditions.