MICROBIAL METABOLIC ACTIVITY AS LEGACY OF AGRICULTURAL MANAGEMENT IN MAIZE AGROECOSYSTEMS FROM MEXICO HIGHLANDS

Background. Soil ecological functions such as C mineralization, enzyme activity, and microbial biomass determine the maintenance of soil fertility in the short and long term. Microbial activity is a sensitive indicator of changes in soils under agricultural management. Objective. Evaluate the metabolic response of soil microbial communities in two temperate maize agroecosystems with different management intensities. Methodology. This study evaluated total soil nutrient concentrations, C mineralization, and microbial metabolic activity by comparing two agricultural regimes. The first one is an intensive regime (IR) characterized by the exclusive use of synthetic fertilizers in a maize monoculture. The second one is a traditional regime (TR) characterized by the use of mixtures of organic matter (maize and bean residues and manure) with synthetic fertilizers in a rotation system of maize and beans. Physical, chemical, and biological properties were tested in the laboratory, and the specific enzyme activity (SEA) and metabolic quotient (qCO2) were calculated. Results. Total soil C concentration was 19% higher in TR (26.6 mg g-1) than in IR (5.1 mg g-1); total C biomass was 30% higher in TR (279 mg C g-1) versus IR (83.9 mg C g-1), and potential C mineralization was 40% higher in TR (356 µg C g-1 d-1) than IR (214 µg C g-1 d-1); in contrast, SEA and qCO2 were lower in TR versus IR. These results support the hypothesis that the microbial community is more efficient under TR than IR because it produces extracellular and intracellular enzymes while growing in biomass. Implications. The present study provides new information about the effect of agricultural management on microbial activity, which is important for farmers not only in Mexico Highlands but also in any agricultural scenario exposed to changes in management practices. Conclusions. Assessment of biological soil properties is a sensitive indicator of changes in soil properties induced by management. Metabolic indices are suitable for the evaluation of ecological functions in cultivated soils.