Newer methods of management and harvesting of sugarcane are being considered to improve soil and water conservation in Brazil. Our aim in this study was to evaluate soil C dynamics under sugarcane cultivation as influenced by the use of conservation management, using measurements from four different management systems and land use histories, i.e. conventional management with preharvest burning, no burning with residue retention and two systems without burning plus additional organic amendments. Field sites also differed in terms of soil texture. We compared field measurements of soil C stocks, 13C and microbial biomass with simulated results from the Century ecosystem model for each of the sites and management histories. We also did long-term simulations of the management treatments and sites to approximate steady-state SOC levels, to explore potential management-induced differences in SOC stocks and interactions with soil texture. The model accurately represented treatment and site differences for total SOC stocks, in which SOC stocks were strongly affected by both rates of organic matter input to soil and soil clay content. However, the model tended to underestimate the relative contribution of sugarcane-derived C to total SOC for sites with high residue and external organic matter amendments. Measured microbial biomass C across the sites was closely aligned with relative amounts of organic matter input but did not appear to be strongly affected by soil texture, whereas the model predicted that both texture and organic matter input rate would impact microbial biomass C. Long-term simulations of the conservation management alternatives suggested that SOC stocks could be maintained at or above levels in the original native Cerradão vegetation, whereas conventional practices using residue burning would result in a reduction of SOC to ca. 60% of native levels. Our results support the use of the CENTURY model as an aid to assess the impacts of different soil management practices on SOC stocks under sugarcane in Brazil.

Pyrolysis temperature and feedstock type used to produce biochar influence the physicochemical properties of the obtained product, which in turn display a range of results when used as soil amendment. From soil carbon (C) sequestration strategy to nutrient source, biochar is used to enhance soil properties and to improve agricultural production. However, contrasting effects are observed from biochar application to soil results from a wide range of biochar's properties in combination with specific environmental conditions. Therefore, elucidation on the effect of pyrolysis conditions and feedstock type on biochar properties may provide basic information to the understanding of soil and biochar interactions. In this study, biochar was produced from four different agricultural organic residues: Poultry litter, sugarcane straw, rice hull and sawdust pyrolysed at final temperatures of 350˚C, 450˚C, 550˚C and 650˚C. The effect of temperature and feedstock type on the variability of physicochemical properties of biochars was evaluated through measurements of pH, electrical conductivity, cation exchange capacity, macronutrient content, proximate and elemental analyses, Fourier transform infrared spectroscopy (FTIR) and thermogravimetric analyses. Additionally, an incubation trial was carried under controlled conditions to determine the effect of biochar stability on CO 2 -eq emissions. Results showed that increasing pyrolysis temperature supported biochar stability regardless of feedstock, however, agricultural properties varied widely both as an effect of temperature and feedstock. Animal manure biochar showed higher potential as nutrient source rather than a 915 Agricultural Sciences C sequestration strategy. Improving the knowledge on the influence of pyrolysis temperature and feedstock type on the final properties of biochar will enable the use of better tailored materials that correspond to the expected results while considering its interactions with environmental conditions.

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SUMMARYThere are currently many devices and techniques to quantify trace elements (TEs) in various matrices, but their efficacy is dependent on the digestion methods (DMs) employed in the opening of such matrices which, although "organic", present inorganic components which are difficult to solubilize. This study was carried out to evaluate the recovery of Fe, Zn, Cr, Ni, Cd and Pb contents in samples of composts and cattle, horse, chicken, quail, and swine manures, as well as in sewage sludges and peat. The DMs employed were acid digestion in microwaves with HNO 3 (EPA 3051A); nitric-perchloric digestion with HNO 3 + HClO 4 in a digestion block (NP); dry ashing in a muffle furnace and solubilization of residual ash in nitric acid (MDA); digestion by using aqua regia solution (HCl:HNO 3 ) in the digestion block (AR); and acid digestion with HCl and HNO 3 + H 2 O 2 (EPA 3050). The dry ashing method led to the greatest recovery of Cd in organic residues, but the EPA 3050 protocol can be an alternative method for the same purpose. The dry ashing should not be employed to determine the concentration of Cr, Fe, Ni, Pb and Zn in the residues. Higher Cr and Fe contents are recovered when NP and EPA 3050 are employed in the opening of organic matrices. For most of the residues analyzed, AR is the most effective method for recovering Ni. Microwave-assisted digestion methods (EPA3051 and 3050) led to the highest recovery of Pb. The choice of the DM that provides maximum recovery of Zn depends on the organic residue and trace element analyzed.Index terms: aqua regia, heavy metals, manure, sewage sludge, compost, degree of humification.( A eficiência de determinação de teores de elementos-traço (ET) é dependente dos métodos de digestão (MD) empregados na abertura de matrizes, que, embora "orgânicas", podem conter constituintes inorgânicos de difícil solubilização. Objetivou-se, em razão do emprego de cinco MD, avaliar a recuperação de teores de Fe, Zn, Cr, Cd, Pb e Ni em 11 amostras de composto comercial, composto de lixo, composto orgânico, esterco de bovino, esterco de codorna, esterco de equino, esterco de galinha, esterco de suíno, lodo de esgoto de duas origens e turfa. Os métodos de digestão estudados foram: digestão ácida por micro-ondas com HNO 3 (EPA 3051); digestão nítrico-perclórica com HNO 3 + HClO 4 em bloco digestor (NP); digestão seca em forno tipo mufla com solubilização da cinza residual com ácido nítrico (MUFLA); digestão em solução água régia (HCl:HNO 3 ) em bloco digestor (AR) e digestão ácida com HNO 3 + H 2 O 2 e HCl (EPA 3050). O método da digestão seca é o que proporciona maior recuperação de Cd nos resíduos orgânicos, mas o método EPA 3050 pode ser uma alternativa para o mesmo fim. A digestão seca não deve ser empregada para determinar os teores de Cr, Fe, Ni, Pb e Zn nos resíduos; entretanto, Cr e Fe são recuperados quando a digestão é feita pelos protocolos nítrico-perclórico e EPA 3050 nas matrizes orgânicas. A água régia é o método de digestão mais eficiente em recuperar o Ni, para a maioria dos...

Brazilian sugar cane production has undergone changes in residue management. To better understand the dynamics of soil C and N in soil organic matter (SOM) fractions resulting from sugar cane management practices, we determined: the effects of different sugar cane management on the C and N content of SOM fractions; the effects of crop management, soil texture, depth and different organic matter additions on changes in 13C/12C and 15N/14N isotope composition; and the amount of SOC derived from different sources. Physical fractionation of SOM was performed for soils cultivated under four sugar cane managements, namely straw burning(SB), green cane (GC) and organic systems consisting of sugar cane grown under GC harvesting with high inputs of organic residues for 4 and 12 years (O-4 and O-12 respectively), as well as from a native vegetation (NV) area (Goianésia, Brazil). Ultrasonic dispersion of soil samples from 0–5, 5–10, 10–20 and 90–100-cm depths resulted in three organomineral fractions (<53, 75–53 and 2000–75µm) and one organic fraction denoted as light fraction (2000–75µm). C and N concentrations, 13C and 15N natural abundance and the proportion of C derived from C4 sugar cane plant residues (C-C4) were determined for each fraction. The C management index (CMI), derived from the total C pool and C lability, is useful in evaluating the capacity of management systems to improve soil quality and was calculated using the NV as the reference. Highest C and N concentrations were found for O-12 and O-4, mainly for the <53-µm organomineral fraction at 0–5cm depth. The 13C and C-C4 values indicated a greater accumulation of C-C4 in SOM fractions in organic compared with burned and unburned systems. GC combined with organic management is a strategy for long-term storage of total C and N in the SOM fraction associated with <53-µm fraction and light fraction. In addition, the highest CMI and its positive relationship with C-C4 in O-12 suggest the role of this system to foster soil quality improvement. The results allow infer regarding the potential of management practices on C accumulation in SOM fractions, which, in turn, can be used as indicators of the effects of land management.