Renewing carbon and re-establishing it again in the soil is one of the valuable means to cope with climate change. there are many technologies for carbon apprehension and storage, but the most important one gaining attention is biochar technology. So, to carbonize and return different biological materials back to the farmland, a comprehensive study was proposed to characterize and evaluate the carbon (C) mineralization of biochars produced from different animal manures and crop straws. Six types of biochars were prepared from animal manures (poultry litter, swine and cattle manures) and crop straws (rice, soybean, and corn straws). the biochars were analyzed for chemical characteristics (elemental variables, thermal decomposition, cation exchange capacity, pH, electrical conductivity, specific surface area, and surface functional groups) and an incubation experiment was conducted to evaluate C mineralization from soil biochar mixture. Biochars produced from crop straws resulted to have more c as compared to the biochars produced from animal manures. concentration of nitrogen was low, while P, K, Ca, and Mg were found reasonably higher in all biochars except swine manure biochar. the plant-derived biochars presented lower co 2 emissions when incorporated to soil at 1 and 2% of C. Varying but all the biochars prepared represented an alkaline pH. Biochars prepared from the crop straws resulted to have more c, alkaline in nature, high cec, low co 2 emissions, can sequester C and more suitable to enhance the soil fertility in comparison to biochars produced from other sources. In the Southern region of Brazil can be found immense amounts of diverse animal manure and plant residues as the region have a massive number of animal farms and crop production. Swine and poultry farms are the principal sources of the manure produced in the region. Rice is cultivated on about 1,000 M ha area 1 , while soybean and corn are also major crops grown in the region (more than 6,000 M ha area) 2. In the region, no-tillage planting system is used to grow crops for a long time, and crop straws are left on the surface at the time of harvesting. There may be noted an uneven decomposition of these organic materials and different environmental impacts can be noticed, such as releasing carbon dioxide (CO 2) into the atmosphere and N can be immobilized by microorganisms or can be escaped into the atmosphere in the form of N 2 O, N 2 and NH 3. Biochar is an alternative and beneficial strategy to dispose-off the animal manures and plant residues rather than keeping them on the place or applying to soil directly 3. Biochar is a solid C rich material obtained from organic waste burning in the absence or low supply of oxygen 4. A massive amount of different biomasses can be found to produce biochars such as animal manures, plant residues, sewage sludge, and agricultural wastes. Its production from different residues and wastes for the use of farm soils may be a valuable means to decrease the negative impacts of emissions (greenhouse gases) from the...

After flooding in rice crops, the Fe 3+ ions from iron oxide minerals are reduced to Fe 2+ in the anaerobic conditions, making it soluble. The excess of Fe 2+ in soil solution can be toxic to plants, resulting in decreasing rice yield. Pyrolyzed materials from rice crop residues, such as rice husk, can be an environmentally friendly option to reduce iron availability in soil solution, provided they have appropriate chemical and physical characteristics regarding iron adsorption. In this study, rice husk biochar (RHB) and rice husk ashes (RHA1 and RHA2) were characterized regarding physical and chemical characteristics and the iron adsorption capacity. The different oxygenation conditions in obtaining the materials resulted in chemical and physical differences (e.g., biochar carbon content of 46% and ashes of 16% and 0.93%), but there were no significant differences related to iron adsorption capacity in aqueous solution. The iron adsorption capacity of the biochar was 5.53 mg Fe 2+ g −1 and of the ashes was 6.74 and 7.22 mg Fe 2+ g −1 for the two materials tested, which demonstrates potential of these materials to mitigate iron toxicity in flooded rice crops.

It has become possible to evaluate the conversion of soil organic matter (SOM) in pastures and arboreal crops due to the difference between the photosynthetic cycles of Eucalyptus (C3) and most grasses (C4). The auto analyzer method coupled to the IRMS (Isotope Ratio Mass Spectrometer) in the present study evaluated the 13C content in soil profiles of Eucalyptus plantations of different ages (2, 10 and 21 years), in natural regeneration areas and natural grazing fields, and estimated the SOM conversion of each crop type of. The initial management of all sampled areas was natural pasture. The following profile layers were evaluated: 0-5, 5-10, 10-20, 20-30, 30-40, 40-50, 50-70 and 70-90cm, and the contribution of Eucalyptus biomass over the years of farming was estimated in the SOM conversion process. After 2 years of planting Eucalyptus, the beginning of pasture carbon conversion process occurred in the surface layer (0-5cm). Ten years after planting, the process of converting organic matter by arboreal crops reached the layers up to 20cm. After 21 years of planting and in natural regeneration areas, the entire profile has already been changed by planting Eucalyptus and native tree species.

Methane (CH 4 ) is the second major greenhouse gas after CO 2 , exerting a significant influence on the climate and the chemistry of the atmosphere. In lowland soil, acetate and H 2 /CO 2 are the most important precursors of CH 4 and formed from organic matter fermentation in an anaerobic environment, giving rise to short-chain organic acids (ethanoic, propanoic, and butanoic), depending on the type of crop residue and the soil management system. Ethanoic acid can be directly converted to CH 4 by methanogenic microorganisms, but propanoic and butanoic acids must be converted to acetate before being converted to CH 4 . This study aimed to quantify, in isolation, the dynamics and CH 4 emission potential of the three short-chain organic acids found in flooded lowland soils with rice crops. The study was carried out in a controlled environment using four standard carbon doses (0, 90, 180, and 270 mg kg -1 ) of ethanoic, propanoic, and butanoic acids. The dynamics and the potential emission of CH 4 from soil were investigated when the acids were applied to flooded soil previously incubated for 20 days. The CH 4 emission dynamics were altered with the application of the three short-chain organic acids to the soil, even using an equal amount of carbon. The faster and more intense emission was achieved with the ethanoic acid application in relation to the other two acids application, while butanoic acid presents slower, delayed, and prolonged dynamics of CH 4 emission. Propanoic acid resulted in the lowest CH 4 emission due to its own stoichiometry and the temperature condition in which the experiment was conducted, which were unfavorable to the hydrogenotrophic bacteria. The addition of short-chain organic acids promoted a priming effect in the soil with conversion values of C to CH 4 above the calculated theoretical values.

Rhizospheric carbon resulting from root exudation is one of the substrates used by the soil microbiota, and reflects methane (CH4) emissions in anoxic environments such as irrigated rice cultivation. With the increase of the photosynthetic capacity of the plant in the reproductive period, there is greater accumulation of biomass which, in turn, increases the rate of root exudation. However, genotypic variations in the physiological aspects of rice plants may be related to the amount of root exudates. Ten cultivars of irrigated rice were evaluated for the exudation rate of total organic carbon (EXRToc), shoot dry matter (SDM), and physiological variables related to photosynthesis during the full flowering (blooming) period. Two experiments were conducted in the greenhouse of the Department of Soils of the UFSM (University of Santa Maria, Santa Maria, RS, Brazil) in a completely randomized experimental design. The cultivars presented significant differences in EXRToc, SDM, and all physiological variables as well as positive and significant correlations between EXRToc and physiological variables. Early cultivars were more inefficient in the physiological variables reflecting reduced values of EXRToc and SDM whereas medium-cycle cultivars were more efficient with larger EXRToc and SDM reflections.