The instrument recorded cone index values and used an ultrasonic transducer to measure the depth of insertion. The OM in the top layer of the soil (0e30 cm) was determined by measuring organic carbon using the dichromate oxidation procedure in which residual dichromate is titrated against ferrous sulfate [34]. Some studies indicate organic carbon recuperation of 60e86%, so an adjustment factor was required [35]. For the analysis biological quality indica- tors, 15 soil samples (core diameter 3 cm) from a depth of 0e10 cm were randomly collected from each plot and pooled. Fresh soils (field moisture) were sieved using a 2 mm mesh and stored at 4 C before testing (within 2 months) for acid phosphatase activity [36], mineralizable N (Nmin) [37], microbial biomass carbon (MBC) [38], average well color development (AWCD) and microbial functional diversity on Eco-BIOLOG! plates, including number of utilized substrates (NUS) and Shannon H0 diversity index (H0), at mid- exponential phase [39]. It was also determined the abundance of earthworms (depth 0e30 cm in 25 25 cm areas, soil replaced after sampling to preserve integrity) [40].