Caracterização de biocarvões derivados de diferentes dejetos animais e resíduos das culturas e seu uso em cultivos de grãos

Abstract

In near future the disposal of organic wastes may be a serious problem in Southern Brazil as the region has plentiful amounts of animal farms and crop production. Preparing biochar can be a strategy to dispose off these organic wastes in a suitable way by getting benefits in agriculture soils. So, according to the availability of the materials, we proposed a study to prepare biochars from swine (SMB), poultry (PMB) and cattle (CMB) manures and from rice (RSB), soybean (SSB) and corn (CSB) straws and I) to characterize on the basis of their chemical and degradation characteristics, and carbon (C) mineralization when incorporated in soil and II) to increase soil pH and reduce Al concentration in soil III) to evaluate the influence of biochars application on wheat in combination with nitrogen fertilizer ((NH4)2SO3) and their residual effect on soybean crop under no tillage system. Biochars were prepared at 450 °C in muffle furnace for 1 h with 10 °C increase in temperature min-1. All biochars were alkaline in nature with pH >9.5. Overall C content and CEC were higher in crop straw biochars than in animal manures biochars. On the other hand, for nutrient contents (N, P, K, Ca, Mg and micronutrients) animal manures biochars presented higher concentration as compared to the crop straw biochars. The Fourier- Transform Infrared Spectroscopy (FTIR) spectroscopy of biochars presented the assurance of the less nutrient loss from the materials during pyrolysis condition at low temperatures. The addition of biochars in soil emitted a small amount of CO2 enhancing the C sequestration in soil. The addition of biochar in soil at rate of 0, 5, 10 and 20 Mg ha-1 increased soil pH and reduced the exchangeable Al up to a certain extent, that confirms that the addition of low temperature biochars can be an appropriate technique to enhance soil pH and decline exchangeable Al contents in acidic soils. The addition of 0, 10 and 20 Mg ha-1 of biochars in undisturbed soil along with ammonium fertilizer increased plant height, and dry mass of wheat grown up to florescence, while the addition of biochars without N showed a slight increase in comparison to control (without biochar and without N). The residual effects of biochars on soybean also presented same behavior to previous crop (wheat), where the previous N application enhanced the soybean plant height and crop straw as well. After the experiments, stratified samples (0-5, 5-10, 10-15, 15-25 cm) were analyzed for NO3 -, NH4 +, P, K, Ca, Mg, pH and exchangeable Al contents. We found that in soil top 5 cm the NO3 -, NH4 +, and P contents were influenced with biochar doses and with application of N but in deeper layers there were no significant differences among biochars, doses as well as N application. Soil pH and exchangeable Al were also affected directly up to 5 cm depth, while with the increase in depth decreases soil pH and increases exchangeable Al contents. Hence, it can be concluded that the biochars prepared from crop straws at low temperature are rich in C contents, have more CEC, presented less C mineralization, and promote soil pH increase and exchangeable Al decrease, when incorporated in soil under incubation conditions, while in greenhouse conditions all biochars were comparatively equal to each other even at different doses. The increase in biochars rate increased the nutrients retention in soil, while no difference occurred between animal manure and crop straw derived biochars. Thus, biochars can be considered a suitable alternative for organic waste disposal, while promoting C sequestration and enhancing soil fertility.