Sensitivity of soil biological indicators in an Argiudoll from the Argentinean Pampas

Abstract

The maintenance of soil quality and crop productivity is an important goal for modern agriculture. Soil tillage systems that improve the soil organic carbon and also favor the survival and activity of soil microorganisms could contribute to the sustainability of agricultural systems. The aim of the work was to assess the changes produced by different management practices (tillage systems and cover crop) on soil biological parameters in order to evaluate their capacity as sensitive soil quality indicators. The trial was carried out at the Agriculture Experimental Station INTA Marcos Juárez (Province of Cordoba-Argentina), with different soil management techniques. Soil organic carbon (OC), microbial biomass carbon (MBC), soil enzyme activities (acid phosphatase, dehydrogenase and urease) and metabolic quotient (qCO<sub>2</sub>) were determined on soil samples (0-7.5 cm sampling depth) at six sampling times.<strong> </strong>The management techniques were: combined tillage (CL), no-tillage (NT) and no-tillage with cover crop (NTCC). An old pasture that has not been tilled since 1993 was also sampled as a reference (R). Soil organic carbon, MBC and soil enzyme activities were higher in the undisturbed soil (R) than in the cropped plots (p < 0.05), while the qCO<sub>2</sub> was significantly lower. The OC decrease was 39.2%, 35.1% and 29.1% for CL, NT and NTCC, respectively. The CL treatment showed lower MCB values (between 50% and 67%) than those found in NTCC. Metabolic efficiency was significantly higher in NTCC than in CL (qCO2 was 32% lower). A lower enzymatic activity (acid phosphatase, urease and dehydrogenase) was found in CL with respect to NTCC (p < 0.05). Soil enzymes were positively correlated with MBC, and OC with MBC. Multivariate data analysis allowed group treatments and a summary variable was obtained that could be interpreted as a simple index of soil quality. The OC was not a sensitive indicator to differentiate management systems. However, it was sensitive enough to detect changes between R with respect the other treatments. Instead, biological parameters allowed for differentiation of effect of different management, identifying the system NTCC as the greatest contributor to the sustainability and biological soil conservation. Microbial biomass carbon is suggested as a sensitive indicator since it is related to various soil functions. Also, the metabolic quotient (qCO<sub>2</sub>) has proved to be a suitable indicator because it determines the metabolic efficiency of the microbial population through the relation between basal respiration per unit of MBC.