Models can help to explain the main interactions, magnitudes, and velocity by which biological processes accumulate soil organic carbon (SOC) in pastures. An explanatory model using Insight Maker software was constructed for each soil under natural and cultivated pastures, using theoretical carbon models and data which were collected monthly in andisol sites. The model was calibrated and validated by comparing the modeled data to the field data until the smallest prediction error was reached. The indicators used were the mean absolute error (MAE), root-mean-square error (RMSE), mean absolute percentage error (MAPE) and the coefficient of determination (R2). In natural pasture soil, the diversification of organic inputs consistently promoted the growth of microbial biomass and metabolic efficiency. In contrast, intensive management of cultivated pastures, involving the removal of plant cover, plowing and low input of organic matter, stressed the microbial community and increased the potential carbon loss through secondary mineralization and surface runoff. The application of modeling indicated that it is necessary to improve agronomic practices in cultivated pastures, to maintain soil cover and to increase the application of organic fertilizer by 1.5 times, in order to reduce stress on the microbial biomass, accumulate SOC, minimize organic matter mineralization and reduce C losses due to surface runoff. Therefore, improving agricultural management based on the understanding of soil processes will allow increasing the potential for SOC storage, while improving pasture sustainability.

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Coffee crop management is guided by an approach of synthetic nitrogen fertilizers application in order to guarantee high production rates; however, this type of management increases soil degradation. A study was conducted in order to evaluate the impact of changing soil nutritional management from Chemical (NPK) to Organic (Farmyard Manure-FYM), and from Chemical (NPK) to Mixed (NPK + FYM) regarding soil quality properties and mineral nitrogen available in coffee agroecosystems; a multi-spatial analysis was carried out considering a unifactorial design; soil samples were taken from depths between 0.10 and 0.20 m in 42 plots; physical and chemical variables were measured (ammonium, nitrates, pH, organic matter, moisture, bulk density and texture). It was found that Chemical Management affects the physical and chemical properties of soil quality (organic matter, humidity, bulk density, and pH), resulting in significant differences (p < 0.05) comparing to Mixed and Organic Management. The lowest level of organic matter was found under chemical management, being of 3% and increasing up to 4.41% under mixed management. Mineral nitrogen availability in the form of ammonium, was not affected by nutritional management. A higher concentration of nitrate was found under Mixed Management (105.02 mg NO3 kg−1), presenting significant differences (p < 0.05) against Chemical and Organic. There was no significant difference between Organic and Chemical Management. The study allowed us to determine that, through coffee organic nutritional management, it is possible to keep suitable soil quality conditions in order to reduce soil degradation, and to keep mineral nitrogen available for the development of coffee plants.

The conversion of forests to agricultural land can dramatically alter soil properties, but soil resistance, which is theability of soil properties or processes to remain unchanged in the face of a specific disturbance or stress, remainsunclear. We evaluated the impact of land use change and agricultural management on changes on an andosol in theCauca department, Colombia, through the analysis of physicochemical variables and biological indicators (dimensionlessresistance index, where +1 is the highest resistance and -1 is the lowest resistance) that allowed the assessment of soilresistance. The land uses analyzed included (1st) forest, which was approximately 100 years of age, plus areas of the same forest (70% of the area), which had been replaced by (2nd) natural pastures and (3rd) forage crops in the year 1985, i.e. 30 years before the observations. All physicochemical variables except soil clay content were significantly affected by the change from forest to natural pasture. Similarly, the change from forest to forage cropping affected all physicochemical variables as well as resulting in a decrease in soil microbial biomass but an increase in microbial activity. We found that the metabolic quotient (-0.32) had the lowest resistance, followed by the microbial coefficient (0.19), microbial biomass (0.32) and microbial activity (0.39), suggesting that soil stress caused by disturbance has a marked impact on the number and activity of the soil microflora. By contrast the change from forest to natural pastures was not associated with any effect on microbial biomass and its activity, suggesting that the continuous input of organic matter to the soil through the supply of organic residues from diversified root systems and nutrients from livestock urine and manure favored the preservation and resistance of microbial processes in the soil. These findings suggest that deforestation to establish natural pasture has less impact on soil stability and health than cultivating the soil following clearing.