EFFECTS OF CROPPING SYSTEMS AND LIMING ON THE ESTIMATES OF THE POTENTIALLY MINERALIZABLE NITROGEN FRACTIONS ON SOILS IN SOUTHWESTERN GOIÁS

Abstract

An aerobic incubation laboratory trial was undertaken to assess the effects of cropping systems and liming of undisturbed soils and soils under conventional tillage and notillage on the cumulative nitrogen mineralization and on the potentially mineralizable nitrogen (No). The estimated No parameters ranged from 187 to 23 mg N kg-1 of soil, with the highest values found in clayey Oxisols and the lowest ones in dystrophic sandy soils (Ultipsamments). The hyperbolic model estimated higher No values than simple and double potential models, regardless of the cropping systems used. No estimated parameters are proportional to organic C, total N, and clay contents, but become lower with the cropping intensity: conventional tillage < no-tillage < undisturbed soils. Simple and double exponential models estimate nearly the same values of No. The double exponential model estimates a fraction of easily mineralizable nitrogen that accounts for less than 2% of total nitrogen. Liming had a depressive effect on nitrogen mineralization in all soils under conventional tillage. Under a no-tillage system liming increased nitrogen mineralization inOxisols, but decreased it in sandy soils.

KEY-WORDS: Organic carbon; nitrogen; cropping systems; liming; cerrados.