Resumo

FERRERAS, Laura et al. Chemical and biological parameters as indicators of soil quality under different managements. Cienc. suelo [online]. 2009, vol.27, n.1, pp.103-114. ISSN 1850-2067.

The aim of the work was to assess the sensitivity of chemical and biochemical parameters in representative soils of the Pampa Region under different managements with the purpose of i) establishing the soil parameters that may have a role as early and sensitive indicators of soil ecological stress and restoration; and ii) comparing the results from cropped plots with the same undisturbed soil type, considered as reference (T). The experiment was carried out on experimental plots under different soil managements at the INTA Experimental Stations at Oliveros, Marcos Juárez and Rafaela. Total organic carbon (COT), organic carbon associated with the fine fraction (COff) and organic carbon associated with the coarse fraction (COfg), microbial biomass carbon (CBM), soil microbial respiration (ARM) and enzymatic activities of acid phosphatase (Pasa), dehydrogenase (Dasa) and urease (Uasa) were determined in composite soil samples. The metabolic quotient (qCO₂), the relationship between ARM and CBM, the enzymatic activities/COT ratio, and the CBM/ COT ratio were also calculated. For each experimental site, cropped plots presented lower values than undisturbed soil in most of the parameters analyzed (p <0.05). The soil cultivation caused large reductions in COT and COfg. The soybean monoculture, at the experimental site Oliveros, had lower Pasa and qCO₂ with respect to corn- soybean-wheat/soybean crop rotation, although the MBC was higher (p <0.05). In Marcos Juarez site, the combined tillage treatment had lower CBM, Pasa, Dasa and Uasa, with respect no-tillage with cover crop (p <0.05). At the Rafaela experimental site, no differences were found in enzymatic activities, although the CBM showed differences between crop rotations. Significant differences were found in qCO₂ at the cropped plots with respect to undisturbed soil at the Marcos Juárez experimental site. The higher values of qCO₂ in cropped plots are indicative of higher maintenance energy of microorganisms. The Pasa/COT ratio in Marcos Juarez and the relationship between Pasa/COT and Uasa/COT in Rafaela, were lower in T than in cropped plots. One plausible explanation is that in cropped soils, organic carbon decreases at a faster rate than the reduction in enzyme activity, and thus the enzyme activity/COT is higher in cropped than in undisturbed soils. Alternatively, extracellular enzymes could bind to humified organic matter to form humoenzymatic complexes. Soil enzymes were positively correlated with COT and COfg. The assessment of biochemical parameters by means of MBC, qCO₂ and enzyme activity of soils under different managements enables short-term changes in soil quality to be monitored. The evaluated soil parameters are shown in some situations be sensitive to anthropogenic disturbance and are well correlated with soil functions.

Palavras-chave : Biochemical soil properties; Microbial biomass; Soil enzymes; Soil organic carbon; Metabolic quotient; Soil quality.

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