DENITRIFICATION ESTIMATES IN MONOCULTURE AND ROTATION CORN AS INFLUENCED BY TILLAGE AND NITROGEN-FERTILIZER

Denitrification in agricultural soils results in loss of N for crop gr owth and production of N2O, a greenhouse gas. Agricultural management must be evaluated for denitrification losses in order to develop minim um N loss systems. Field estimation of denitrification losses is neces sary to evaluate crop management effects. Two methods of field denitri fication measurements, a soil core (SC) incubation and an in situ clos ed chamber (CC), were assessed in monoculture corn (Zea mars L.) and c orn in rotation with soybean (Glycine max L. Merill) and alfalfa (Medi cago sativa L.). Relative estimates of denitrification by the two meth ods depended on soil texture, with the CC method showing more treatmen t effects. Denitrification losses were higher with no-till than conven tional tillage at one site, and were generally higher with corn than s oybean. Nitrogen losses were linear with added N in monoculture corn p lots, and ranged from 1.1 to 4.1% of added N. Losses were not related to added N in corn following alfalfa or soybean. Ratios of N2O/(N2O N-2) aS measured with the SC method were lower at the Ste. Rosalie (1) site than at the Chicot site (0.95 to 2.84), but ratios of N2O/(N2O N-2) measured with the CC method were similar for the sites, from 0.4 6 to 1.20. Denitrification losses measured by either method were relat ed to soil moisture and nitrate content in the soils. Corn production should be carried out with conventional tillage and minimum fertilizer N rates for minimum denitrification.