8 Intanational Sodety for Tropical Ecology ' LOW SOIL NITROGEN MINERALIZATION RATES IN A HUMID TROPICAL PASTURE

Abstract: E x ~ m t l y low in-situ N mkaalization and nitrification rates wac observed in a grazed pasturein which the topsoils remained &nstantly near fidd capacity. Laboratory incubations s h o d that a single fivc day d&ng period followed by rewetting innrased M anintralization and nitrification rates seven-fold and that thne succcssibc wetting and drying cycles incxwsed the rate fourteen-fold. I I RCsmC: Des tam tx~mcmenr faibla de rnineralisation et dc nitrification dc l'azotc ont it6 obsmes in situ dans un pahnage dont les hairone superieurs du sol rrstcnt constarnmcnt prcs de la capacitc au champ. I f i incubaaons au laborat & montFtnt qu'une s d c period =he & 5 jours suivic-d'.unc rehumidification multiplic; par 7 Ics taux dc minaalisaton ct dc nitrification de I'azotc, et que trois cydu successifs d ' humidification et de I sechercsse multiplient les tam par 14.