Eficiência agronômica de fertilizantes à base de micronutrientes com biochar

Abstract

Biochar, a byproduct of pyrolysis, can be combined with micronutrients to create composites that enhance nutrient delivery to crops. This study focuses on the development of biochar-based composites enriched with boron (B), copper (Cu), and zinc (Zn), aiming to enhance the nutrient supply for eucalyptus, wheat, and maize seedlings. Due to the high cost and scarcity of micronutrients, utilizing biomass enriched in B, Cu, and Zn integrated into the organic biochar matrix offers a promising approach to meet crop’s nutritional demands. The objectives of the study were: i) to produce and characterize biochars from various biomasses combined with both soluble and insoluble sources of B, Cu, and Zn under different pyrolysis temperatures; ii) to investigate the release kinetics of B, Cu, and Zn and their effects on the availability and residuality of these micronutrients in contrasting soils; and iii) to evaluate the agronomic value and efficiency of biochar-based composites in the cultivation of eucalyptus, wheat, and maize. The biochar composites were prepared from chicken manure, shrimp carcass and sewage sludge, doped separately with boric acid, borax, copper sulfate, copper oxide, zinc sulfate and zinc oxide, and the mixtures were pyrolyzed at temperatures of 300 °C and 550 °C. The composites were analyzed using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) and tested for Cu release kinetics in 2% citric acid. The agronomic efficiency of the composites was evaluated in three experiments with eucalyptus, wheat and maize plants, grown in two different Oxisols. The study used a completely randomized design with three replicates, and the impact on crop nutrition and growth was evaluated. FTIR confirmed successful B integration into the biochar matrix, with the CSC-BA: shrimp waste + boric acid at 300 °C; composite at 300 °C demonstrating notable thermal stability, B retention, and availability, enhancing B release kinetics. In Experiment 2, FTIR analysis confirmed the incorporation of Cu, with the CSS/CS-5: sewage sludge + copper sulfate at 550°C composite showing superior agricultural performance, reducing Cu release into water and enhancing Cu accumulation in wheat shoots. CSS/CS-5 maintained low Cu concentrations, indicating controlled release that meets wheat's high Cu nutritional demands. In Experiment 3, Zn-doped composites, particularly at 300 °C, exhibited higher Zn release and improved Zn availability for maize growth. The composites effectively met the nutritional demands of maize seedlings and showed promise in enhancing crop performance. Overall, the study demonstrated that biochar-based composites enriched with B, Cu, and Zn effectively supply micronutrients to eucalyptus, wheat, and maize, meeting their nutritional demands compared to commercial mineral sources.