Carvões pirolítico e hidrotérmico como estratégia para economia de fertilizantes minerais na agricultura

Abstract

Given the limitations in the production of mineral fertilizers, it is essential to explore alternative nutrient sources for agriculture, such as carbonaceous materials. However, depending on the characteristics of these materials, influenced by the production method, their use may be more effective when combined with mineral fertilizers (MF). Based on this, two hypotheses were tested: in relation to hydrochar (HC), pyrochar (PC) from cashew bagasse is more effective as a nutrient source for maize crops; and the application of charcoals combined with mineral fertilizers allows for a reduction in the use of these inputs. The aim of this study was to evaluate the fertility of degraded soil and the initial development of maize plants after fertilization with pyrolytic and hydrothermal cashew bagasse charcoals applied individually and in combination with mineral fertilizers. The experiment was conducted in a greenhouse, in a completely randomized design, with 6 treatments and 6 replications. The treatments were: Control (T0);100% MF (T1); 100% HC (T2); 100% PC (T3); 50% MF + 50% HC (T4); and 50% MF + 50%PC (T5). At the end of the experiment, gas exchange, photosynthetic pigments, dry biomass, and the accumulation of macro and micronutrients in the plants were analyzed, along with soil chemical analyses. Statistical analysis consisted of analysis of variance (ANOVA) and Duncan's test for mean comparison at a 5% significance level using SAS academic version software. The highest values for gas exchange were obtained by T1, T2, and T5, with an average net photosynthesis of 27.2 μmol CO₂ m⁻² s⁻¹. However, T0 and T3 increased chlorophyll content by an average of 34.9% compared to the other treatments. For growth variables, T5 provided the greatest benefits. Total plant dry biomass was higher for T1, T4, and T5 (24.77, 22.99, and 23.19, respectively). Treatments T2 and T4 allocated more resources to root production, with the root mass ratio showing an average increase of 14.6% compared to T0. The accumulation of macronutrients in the leaf biomass was higher for T1 and T5, as well as for micronutrients, except for Mn. Soil fertility attributes were improved by T1, T4, and T5. The isolated application of HC and PC from cashew bagasse did not effectively improve the initial development of maize and degraded soil fertility. However, the application of charcoals together with MF provided beneficial results and reduced the need for fertilizers. Among the charcoals, PC provided greater benefits compared to HC.