Spatio-temporal patterns of soil microbial and enzymatic activities in an agricultural soil.

AON M; CABELLO M; SARENA E; ALEJANDRO COLANERI

APPLIED SOIL ECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2001

0929-1393

In the general context of the search of a quality index for soil as an indicator of sustainable management, we analyzed a soil recently subjected to agriculture from the ?El Salado? river basin (Buenos Aires, Argentina) under no-till or conventional tillage (CT). We sought to detect whether a pattern of interactions among microbial, biochemical and physico-chemical variables in soil exists that may be distinguished and characterized. Several microbial groups, enzymatic activities and O2 and CO2 exchange rates were monitored before planting (T0) and during the growth cycle of soybean (Glycine max (L.) Merr.) (T1: flowering stage; T2: pre-harvest period). Strong relationships were evidenced by correlation r (r2) matrices performed with several specific groups of bacteria and fungi, and soil enzymatic activities representative of main nutrient cycles (C, N, P). A burst of biological activity was registered at T1 as could be judged through: (i) a remarkable increase in the numbers of microorganisms measured at both depths tested (D1: 5?10 cm; D2: 15?20 cm); (ii) a peak of O2 consumption; (iii) a maximal gradient of activity exhibited by all enzymes tested (acid and alkaline phosphatases, dehydrogenase, FDA hydrolysis,
-glucosidase, urease). Microorganisms stratified as a function of depth particularly at T0 and T2, whereas at T1 they appeared to transiently redistribute in the 5?20 cm profile unlike all enzymatic activities that showed a maximal stratification. Low respiratory quotients, RQ (∼=0.2; RQ, defined as the ratio of qCO2 over qO2 ), were found, following an experimental method for quantifying rates of O2 consumption, qO2 , and CO2 production, qCO2 , by soil, and a mathematical model developed by ourselves to interpret the data [Soil Sci. 166 (2001) 68]. The biodiversity of fungi increased 16% at T2 with respect to T0 along with a 37% increment in species richness. The fact that several of the variables measured were strongly linked despite season and crop presence, points to the existence of a core of highly interrelated processes in soil.