BASAL AND SPECIFIC MICROBIAL RESPIRATION IN SEMIARID AGRICULTURAL SOILS - ORGANIC AMENDMENT AND IRRIGATION MANAGEMENT EFFECTS

Evolution of microbial activity in semiarid agricultural soils was studied measuring the basal (CO2 evolved) and specific microbial respiration (qCO(2)). The effects of straw residue management (buried or removed), irrigation (dry or irrigation farming), and chemical composition of the soils (calcareous, gypsiferous, or saline) were analyzed. Seasonal samplings were carried out over a 2-year period. Both irrigation management and harvest residue management, as well as soil chemical composition, influence basal respiration significantly. Straw burying and water addition increased soil respiration in every sampling. On annual average, calcareous soils, with low levels of gypsum and salts and higher percentage of organic carbon, evolved the highest rates of carbon dioxide. Basal and specific microbial respiration were positively and significantly correlated. The release of carbon dioxide per unit of microbial biomass (qCO,) was considerable in the experimental soils, especially with buried straw, although basal respiration was low. High levels of qCO(2) were related to severe climatic conditions and management disturbances (ploughing action, fluctuation of organic carbon content), stressing factors that rejuvenate microbial population.