Fig. 2. Changes in enzyme activities and aggregate stability in the different soil samplings. For each sampling point, bars denoted by the same letter are not statistically
different according to Tukey’s test at the 5% probability level. NS: not significant, *, ** and ***: significant at probability level P < 0.05, 0.01 and 0.001, respectively. INTF: iodonitrotetrazolium
formazan and PNP: p-nitrophenol. Sampling time S1: after the first application of organic materials but before watermelon planting, S2: after watermelon
cropping, first year, S3: after cauliflower cropping, first year, S4: after watermelon cropping, second year and S5: after cauliflower cropping, second year. The mineral fertiliser
treatment was not evaluated at the first sampling because the fertiliser was applied after soil sampling S1.