INFLUENCE OF TILLAGE SYSTEM ON DENITRIFICATION IN MAIZE-CROPPED SOILS

Denitrification losses show an irregular pattern through the year, oft en being caused by climatic conditions and management practices. The o bjectives of the present work were to quantify denitrification losses and to determine the influence of tillage system on the factors that c ontrol denitrification in fertilized soils. The modal profile of the s oil was an Vertic Argiudoll, clay loam texture, located in Buenos Aire s province, Argentina. The treatments were: (a) fertilized, (b) incorp orated fertilization and (c) without fertilization for both no tillage and conventional tillage systems. Chambers were placed in the field t o measure denitrification. In this clayish soil the estimated mean val ues of accumulated denitrification during the crop cycle (90 days) wer e 0.190 kg N ha(-1) for conventional tillage and 0.350 kg N ha(-1) for no tillage. In treatments with no tillage, losses by denitrification were approximately twice those of conventional tillage. These differen ces were also evidenced by the number of microorganisms, which were si gnificantly higher (P<5%) for no tillage on all dates, except for at f lowering. The increase at flowering coincided with the period of highe st rainfall and consequently the highest water contents in the soil. T he highest denitrification losses, except for sowing, were measured wh en soil moisture content was more than 30% (v/v). Denitrification incr eased in conjunction with an increase in the availability of carbon th at is consumed by the heterotrophic microorganisms (including the deni trifiers).