Interaction between gas exchange rates, physical and microbiological properties in soils recently subjected to agriculture

The impact of conventional tillage (CT) or no-till (NT) management on soil microbial respiration as well as microbial abundance was studied in soils f rom the El Salado basin river (Buenos hires, Argentina) recently subjected to agriculture under a corn-pasture rotation since 1996. Both management sy stems were monitored for several soil (micro)biological, physical and chemi cal properties during the second (1997) to fourth (1999) years from the beg inning of the experiment. O-2 and CO2 composition of the soil atmosphere an d the rate at which soil consumes O-2 (qO(2)) or produces CO2 (qCO(2)), und er conditions that approximate the soil environment in the field, were quan titated Following an experimental method and a mathematical model developed by ourselves [Soil Sci. 166 (2001) 68] To interpret the data. qO(2) and qC O(2) expressed in terms of kg O-2 or CO2-C per ha per day or per kg C of mi crobial biomass (microbial respiration), increased from the lowest values m easured at 10-30% water-filled pore space (WFPS) up to 60% WFPS, decreasing thereafter. Low respiratory quotients, RQ (qCO(2)/qO(2) < 1.0), were detec ted, with gas exchanges being slightly higher in NT than in CT. Correspondi ngly. higher bacterial and fungal biomass were measured in NT than in CT. A pparently, bacteria were more sensitive to high WFPS than fungi. When aerob ic bacteria or fungi counts were compared at low or high WFPS, they differe d significantly only in the upper soil profile whereas microaerophilic bact eria and fungi were significatively different in both depths tested (D1 = 5 -10 cm; D2 = 15-20cm). The results are discussed in terms of microbial meta bolism behavior and abundance as a function of management and soil air/wate r balance in soils recently subjected to agriculture. (C) 2001 Published by Elsevier Science B.V.