Short-term response of physical and chemical aspects of soil quality of a kaolinitic Kandiudalfs to agricultural practices and its association with microbiological variables

We evaluated the short-term (three years) impact of agricultural practices (soil tillage methods, maize cropping systems, and Brachiaria fallow) on the physical and chemical aspects of soil quality (SQ) of a kaolinitic Kandiudalfs in Northeastern Brazil, and the correlation between SQ and microbiological variables. A forest site was also sampled as reference of undisturbed soil. SQ was evaluated by multivariate analyses of total and particulate organic matter carbon, cation exchange capacity, mean weigh diameter and percentage of water stable aggregates of soil samples (0–20 cm depth). Phospholipid fatty-acids were used to quantify microbial biomass (MB), fungi to bacteria ratio (F/B) and an indicator of bacterial stress (19:0cy/18:1ω7c), whereas microbial enzyme activity was determined by the hydrolysis of fluorescein diacetate (FDA). A gradient of SQ, described by increases in the values of physical and chemical variables, was observed according to the sequence: cropped areas, irrespective to the agricultural practices < Brachiaria fallow < forest. SQ was positively correlated with MB, F/B and FDA, and negatively with 19:0cy/18:1ω7c. F/B was more sensitive than SQ to the agricultural practices. In the short term, the physical and chemical aspects of the quality of a kaolinitic soil is restored by Brachiaria fallow, but is not affected by tillage methods or maize + pigeonpea intercropping. F/B ratio is a potential predictor of changes in the quality of kaolinitic soils in response to agricultural practices.