Soil β-Glucosidase activity after 28 years of continuous sewage sludge application vs. mineral fertilizers

Sewage sludge (SS) recycling in agriculture is a sustainable alternative to improve soil quality and increase agricultural production. However, the presence of pollutants can directly impact microbial activity. The enzyme β-glucosidase plays a key role in the carbon cycle, reflecting the response of soil health to changes in management. There is still little research evaluating the influence of continuous applications of sanitary SS on soil β-glucosidase activity. A long-term experiment was conducted under field conditions in Jaboticabal, SP, Brazil, with the objective of evaluating the application rates of SS for 28 years vs. mineral fertilizers on the activity of the enzyme β-glucosidase in a clayey dystrophic Red Latosol. The experimental design was randomized blocks with four treatments and five replications. The treatments consisted of conventional mineral fertilization (CMF) and three cumulative rates of SS (125, 250, and 447 Mg ha -1 , dry basis). Soil samples were collected from the 0–0.1 and 0.1–0.2 m layers. Soil enzymatic activity was then determined by the p-nitrophenol colorimetry method. The results were subjected to descriptive statistics and, once normality was verified by the Shapiro-Wilk test, analysis of variance was applied at a significance level of 5% (F test) and the means were compared by the Tukey test (p ≤ 0.05). The highest soil β-glucosidase activity occurred in the 0–0.1 m layer, where the results ranged from 73.56 to 94.70 mg p-nitrophenol kg -1 soil h -1 . In the 0.1–0.2 m depth layer, the values ​​ranged from 58.08 to 70.60 mg p-nitrophenol kg -1 soil h -1 . The treatment that received only CMF and the 447 Mg ha -1 SS dose showed the lowest enzyme activities. On the other hand, the activity of the β-glucosidase enzyme was higher at the dose of 250 Mg ha -1 in the 0.0–0.1 m layer. Proper management of SS application rates in agricultural soils is essential to increase nutrient availability and enhance the contribution of OM (high C sequestration), without impairing microbial activity (soil health). The results of this study are aligned with the concepts of circular economy and the 'Sustainable Development Goals' (SDGs) of the UN 'Agenda 2030', with emphasis on 'SDG2', 'SDG3' and 'SDG13'.