Combined use of biochar and phosphate rocks on phosphorus and heavy metal availability: A meta-analysis.

Biochar (BC) and phosphate rocks (PR) are alternative nutrient sources with multiple benefits for sustainable agriculture. The combination of these soil amendments serves two main purposes: to increase soil phosphorus (P) availability and to remediate heavy metal (HM) contamination. However, a further demonstration of the benefits and risks associated with the combined use of BC and PR (BC + PR) is needed, considering the specific characteristics of raw materials, soil types, experimental conditions, and climatic contexts. This meta-analysis is based on data from 28 selected studies, including 581 paired combinations evaluating effects on extraction and fractionation of cadmium (Cd) and lead (Pb), and 290 paired combinations for soil labile and non-labile P. The results reveal that BC, PR, and BC + PR significantly increase soil labile and non-labile P, with BC + PR showing a 150% greater increase compared to BC alone. In tropical regions, substantial increases in P levels were observed with BC, PR, and BC + PR exhibiting increments of 317, 798, and 288%, respectively. In contrast, temperate climate conditions showed lower increases, with BC, PR, and BC + PR indicating 54, 123, and 88% rises in soil P levels. Moreover, BC, PR, and BC + PR effectively reduce the bioavailability of Cd and Pb in soil, with BC + PR demonstrating the highest efficacy in immobilizing Cd. The synergistic effect of BC + PR highlights their potential for Cd remediation. BC + PR effectively reduces the exchangeable fraction of Cd and Pb in soil, leading to their immobilization in more stable forms, such as the residual fraction. This study provides valuable insights into the remediation potential and P management benefits of BC and PR, highlighting their importance for sustainable agriculture and soil remediation practices.

"Effects of soil management, rotation and sequence of crops on soil nitrous oxide emissions in the Cerrado: A multi-factor assessment".

The emission of nitrous oxide (N2O), one of the main greenhouse gases, which contributes significantly to global warming, is a major challenge in modern agriculture. The effects of land use systems on N2O emissions are the result of multiple variables, whose interactions need to be better understood. In this sense, this study analyzed the possible effects of different soil managements, crop rotations and sequences, as well as edaphoclimatic factors causing N2O emissions from soils in the Cerrado biome (scrubland). The following four land-use systems were evaluated: 1) No-tillage cultivation with biennial crop rotations and sequences: legume-grass and alternating grass-legume crops in the second season - NT-SS/MP; 2) No-tillage with biennial rotations and sequences: grass-legume and alternating second crop of legume-grass - NT-MP/SS; 3) Conventional planting with disc harrow and biennial legume-grass rotation-CT-S/M; and 4) Native Cerrado (CE), no agricultural land use. The legume and grass species, planted in the two no-tillage treatments were soybean, followed by sorghum BRS3.32 (Sorghum bicolor (L.) Moench) (SS), and maize, followed by pigeon pea (Cajanus cajan) (MP). Nitrous oxide emissions were evaluated for 25 months (October 2013 to October 2015), and the results were grouped in annual, total, growing and non-growing seasons, as well as yield-scaled N2O emissions. The mean N2O fluxes were 24.14, 15.71, 32.49 and 1.87 µg m-2 h-1 in the NT-SS/MP, NT-MP/SS, CT-S/M and Cerrado areas respectively. Cumulative N2O fluxes over the total evaluation period from the systems NT-SS/MP, NT-MP/SS, CT-S/M and CE, respectively, were 3.47, 2.29, 4.87 and 0.26 kg ha-1. A correlation between N2O fluxes and the environmental variables was observed, with the exception of water-filled pore space (WFPS), but N2O peaks were associated with WFPS values of >65%. In the 2014-2015 growing season, yield-scaled N2O emissions from NT-MP/SS were lower than from CT-S/M. A multi-factor approach indicated that conventional management with main season soybean or maize and no alternating crop sequence intensifies soil N2O emissions in the Cerrado.

Dynamics of potassium released from sewage sludge biochar fertilizers in soil.

The solid product of sewage sludge (SS) pyrolysis, called SS biochar (SSB), is rich in carbon and nutrients, such as phosphorus (P), nitrogen (N), calcium (Ca), and zinc (Zn). However, SSB has a low potassium (K) concentration because it is released with water during the final stage of sewage treatment. The enrichment of SSB with mineral sources of K can solve the low supply of K in SSB and produce an organomineral fertilizer with a slow release of K. However, the dynamics of K release from these enriched fertilizers in different soil types remain unclear. This study investigated the dynamics of K release from biochar-based fertilizer (BBF) in the form of pellets and granules in two soil types (clayey and sandy) and natural silica. An incubation experiment was conducted for 60 days, and replicates were evaluated at prescribed time intervals. After the incubation period, the levels of K available in the solid fraction were determined, and the dynamics of K release were evaluated using four nonlinear regression models. BBFs achieved a slower release of K than the mineral KCl. The dynamics of K release were affected by the physical form of BBF, such that the pelleted BBF exhibited the slowest K release. Furthermore, regarding the concentration detected in the solid phase, the total released was highest in clayey soil, followed by sandy soil and natural silica. The enriched BBFs reduced K release throughout the experimental period, behaving as slow-release fertilizers with the potential to optimize K uptake by plants throughout the growth cycle. Further studies are required to evaluate K leaching and retention in the soil profile when biochar-based fertilizers are applied.

Nitrogen Use Efficiency in an Agrisilviculture System with Gliricidia sepium in the Cerrado Region.

Gliricidia (Gliricidia sepium) is a tree legume that has great potential for use in agriculture because of its multiple-use characteristics. However, there is little information in the literature about the effect of agrisilvicultural systems on nitrogen (N) cycling. This study evaluated the effect of densities of gliricidia on N cycling under an agrisilvicultural system. The treatments were composed of different densities of gliricidia: 667, 1000 and 1333 plants ha-1, with a fixed spacing of 5 m between the alleys. The efficiency of N use was investigated by using the 15N isotope tracer. In each plot, a transect perpendicular to the tree rows was established in two positions: (i) in the corn (Zea mays) row adjacent to the trees, and (ii) in the corn row in the center of the alley. The N fertilizer recovery efficiency ranged from 39% in the density of 667 plants ha-1 to 89% with 1000 plants ha-1. The effect of gliricidia on the N uptake by corn was higher in the central position of the alley with 1000 plants ha-1. The agrisilvicultural system with 1000 plants ha-1 was highly efficient in the recovery of mineral N, representing an excellent option for integrated production systems in tropical regions.

Assessing potassium release in natural silica sand from novel K-enriched sewage sludge biochar fertilizers.

Enrichment of biochars to produce slow nutrient release fertilizers with minimal losses to the environment is a promising strategy. However, the release of potassium (K) from biochar-based fertilizer produced from sewage sludge (SS) is still poorly studied. In the present 30-day incubation study, the dynamics of K release were evaluated from SS biochar-based fertilizers enriched with potassium chloride (KBF) in different forms, subjected to two levels of silica sand moisture (10 and 20%). The KBF was evaluated in the form of granules, pellets and powder, in addition to pure KCl mineral fertilizer. During the incubation period water-soluble K extractions were performed, where the K contents were adjusted to K release kinetic models. An additional experiment was performed to assess the effect of KBFs and KCl on K leaching. In general, at both moisture levels all KBFs presented a slower K release compared to pure KCl mineral fertilizer, reducing the release rate by up to 77%. The K release dynamics were affected by the type of biochar fertilizer (granule, pellet and powder) and the silica sand moisture level. The behavior of KBFs as slow-release fertilizers is strongly dependent on the silica sand moisture level. At the 10% moisture level, biochar fertilizers in the form of pellets and granules can be classified as slow-release fertilizers with the potential to increase the efficiency of K use in agriculture. Furthermore, compared to the chemical fertilizer, KBF reduced the amount of leached K, diminishing the risk of this nutrient polluting the groundwater. Our results must be further assessed in real conditions using soil as a suitable medium for agronomic and environmental evaluation. Therefore, future studies should consider the dynamic of K and other nutrients from KBFs in distinct soil types.

Biochar increases soil carbon pools: Evidence from a global meta-analysis.

Biochar is a carbon-rich material that increases soil C sequestration and mitigates climate change. However, due to the variability of experimental conditions, types of biochar and soil, the influence of biochar on the accumulation of different soil carbon fractions remains unclear. Therefore, a meta-analysis was performed that included 586 paired comparisons obtained from 169 studies conducted in various countries around the globe. The data set average showed significant relative increases of 64.3, 84.3, 20.1, 22.9 and 42.1% for total C, organic C, microbial biomass C, labile C and fulvic acid, respectively. The dissolved organic C, humic acid and humin fractions showed no significant variations. The relative increase in TC was favored by increasing biochar rates applied to fine-textured soils with low C content in temperate climate regions seen through short-term experiments conducted under controlled conditions. This behavior was different for each soil C fraction. Therefore, variations between experimental conditions, types of biochar and soil show that it is necessary to consider multiple factors when choosing the conditions of biochar use to maximize C sequestration in the soil and/or the increase of labile C fractions in the soil.

Pyrolysis of Sewage Sludge: Physical, Chemical, Morphological and Mineralogical Transformations

Abstract The sewage sludge (SS) use in agriculture has been limited by the Brazilian legislation to a few situations, mainly as a precautionary measure due to inorganic pollutants and pathogens. Thus, a large amount of SS has been accumulated in landfills, with no prospect of use, generating great concern for governments and society. Thermal treatment via pyrolysis has stood out as an option for SS recycling, transforming it into a carbon-rich product known as SS biochar (SSB). Biochar from SS showed good potential to be used for agricultural and environmental purposes. The present study aimed to evaluate the influence of pyrolysis at 300°C on the physical, chemical, morphological and mineralogical characteristics of SSB. In general, pyrolysis increased total carbon, total nitrogen, macro and micronutrient contents, except potassium. Pyrolysis also increased heavy metals (HMs) concentration in SSB. However, HMs values remained below the maximum limits allowed according to the legislation on SS agricultural use. X-ray analysis showed that both SS and SSB present silica (SiO2) as the main mineral. Pyrolysis also increased the SS surface area (SA) and porosity. In general, results of the present study prove showed that pyrolysis is a technological alternative to enable SS use as a sustainable input in agriculture.

A scoping review on biochar-based fertilizers: enrichment techniques and agro-environmental application.

Biochar is a carbonized biomass that can be used as a soil amendment. However, the exclusive use of biochar may present some limitations, such as the lack of nutrients. Thus, biochar enrichment techniques have made it possible to obtain biochar-based fertilizers (BCFs), with great potential to improve soil fertility. Nevertheless, there is still a lack of information about the description, advantages, and limitations of the methods used for biochar enrichment. This review provides a comprehensive overview of the production methods of enriched biochar and its performance in agriculture as a soil amendment. Studies demonstrate that the application of BCF is more effective in improving soil properties and crop yields than the exclusive application of pure biochar or other fertilizers. The post-pyrolysis method is the most used technique for enriching biochar. Future studies should focus on understanding the mechanisms of the long-term application of BCFs.

Novel K-enriched organomineral fertilizer from sewage sludge-biochar: Chemical, physical and mineralogical characterization.

Sewage sludge biochar (SSB) is a multi-nutrient fertilizer with very low K concentration. This study presents a novel K-enriched SSB fertilizer with the potential to increase K use efficiency by crops. The object of this work was therefore to evaluate the physical-chemical, morphological and mineralogical characteristics of a SSB organomineral fertilizer (OSSB) enriched with K. SSB was enriched with KCl and K2SO4 using three technological methods (granules, pellets and powders). The enrichment of SSB with K ensured a K2O content about 75 times higher than the pure SSB. Organominerals in powder form had higher levels of total nitrogen, calcium, sulfur, phosphorus and higher pH than granules and pellets. The morphology and physical characteristics of enriched OSSBs were more influenced by the form of the fertilizer than by the source of K. In general, the enriched OSSBs are influenced by the quantities of feedstocks and the enrichment technology.

Assessing the potential of sewage sludge-derived biochar as a novel phosphorus fertilizer: Influence of extractant solutions and pyrolysis temperatures.

Sewage sludge-derived biochar (SSB) is a phosphorus (P) source with potential to replace soluble P fertilizers. However, SSB presents a diversity of P compounds, mainly in mineral forms with different degrees of chemical stability. This hinders the prediction of P bioavailability. In the present study we evaluated P solubility and bioavailability using different chemical extractants. Additionally, the relationships between extractable P and physicochemical properties were evaluated for SSB obtained over a wide range of temperatures (200 °C; 300 °C; 500 °C and 600 °C). Available phosphorus content was extracted using 2% citric acid (P-CA), neutral ammonium citrate + water (P-NAC) and Mehlich 1 solution (0.0125 mol L-1 H2SO4 + 0.050 mol L-1 HCl). Physicochemical properties and extractable P were strongly affected by pyrolysis temperature. Higher pyrolysis temperature resulted in increased pH, BET surface area, pore volume, ash, fixed carbon, Ca, Mg and Zn contents, as well as formation of stable Ca minerals (calcite and oxalate). The total P content increased with pyrolysis temperature (≥300 °C). Nevertheless, the solubility of biochar-P in the extractants presented different trends with temperature. The P-NAC content reached a maximum (79% of TP) at 300 °C and then declined at higher temperatures. Only at 600 °C P-CA and available P were affected by the temperature, where the P-CA increased and available P decreased. Therefore, it is recommended that the P solubility in different extractants should be considered when using SSB as an alternative to inorganic P fertilizers.

Long-term effects of sewage sludge-derived biochar on the accumulation and availability of trace elements in a tropical soil.

Thermal treatment by pyrolysis has been proposed as a sustainable alternative to enable the agricultural use of sewage sludge. The solid product obtained via pyrolysis of sewage sludge is called sewage sludge biochar and presents several advantages for its use as a fertilizer or soil conditioner. However, there are concerns about the accumulation and dynamics of trace elements in soil amended with sewage sludge biochar over the years. This study examined the effect of sewage sludge biochar, under field conditions for 5 yr, on the accumulation and availability of trace elements in a tropical soil. For this, 15 t ha-1 of sewage sludge biochar produced at 300 and 500 °C were applied in the first two growing seasons. Application was interrupted from the third to the fifth seasons to assess the residual effect of sewage sludge biochar in the soil. The total and available trace element concentrations were determined. The total contents of trace elements showed the following variation in the soil over the 5 yr (mg kg-1): Cd (16.8-20.0), Co (19.5-21.5), Cr (98.2-125.7), Cu (8.1-17.1), Mn (62.9-85.7), Ni (20.3-35.0), Pb (27.0-52.4), and Zn (20.3-35.8). There was no change in the availability of Cd, Cr, Ni, and Pb over the years. Additionally, a residual effect of the sewage sludge biochar was the increase in availability of trace elements that are considered essential (Cu, Mn, and Zn) and beneficial elements (Co) for plants. Therefore, in relation to contamination by trace elements, the pyrolysis of sewage sludge of domestic origin proved to be an adequate strategy to enable the safe use of this residue in tropical agriculture.

The residual effect of sewage sludge biochar on soil availability and bioaccumulation of heavy metals: Evidence from a three-year field experiment.

Conversion of sewage sludge (SS) into biochar through pyrolysis is an alternative to make this residue useful for agricultural purposes. Despite advances in interpreting the functions of SS biochar (SSB) for improving soil quality, it is still necessary to understand its residual effect on the dynamics of heavy metals (HM), especially under field conditions in tropical soils. Therefore, the objective of this study was to evaluate the residual effect of the application of SSB obtained at different pyrolysis temperatures on the accumulation, availability and bioaccumulation of HMs by corn cultivated in a tropical soil. For this purpose, a field experiment was conducted for three years to assess the total and available levels of HMs in the soil and the leaf concentration after suspending the application of 30 t ha-1 of SSB produced at 300 °C (BC300) and 500 °C (BC500). In general, the HM contents were below the maximum allowed by environmental legislation in several countries. SSB, regardless of temperature, was effective in immobilizing non-essential HMs for plants, such as Cd, Co, Cr and Pb, in the soil. On the other hand, SSB was able to supply micronutrients to corn plants after amendment ceased. Thus, the lack of negative long-term effects confirms the feasibility and safety of using SSB in agricultural areas with regards to contamination by HM, and makes it an alternative for the disposal of domestic SS.

Sewage Sludge Biochar Effects on Phytopathogenic Fungi and Beneficial Microorganisms

Abstract Biochar (BCH) is a solid product, rich in carbon, obtained by heating biomass under controlled conditions of oxygenation, in a process known as pyrolysis. Its benefits are associated with improvements to the physical, chemical and biological properties of soil. Furthermore, BCH can affect the growth of phytopathogenic microorganisms. Despite research advances in this area, there is still a lack of information on the effect of BCH concentration on different soilborne microorganisms. This work evaluated the direct effect of sewage sludge biochar (SSB) on the in vitro growth of different soilborne fungi. Eight phytopathogens [Fusarium oxysporum, F. oxysporum f. sp. lycopersici (CEN 1456), Macrophomina phaseolina (429), Sclerotinia sclerotiorum, S. sclerotiorum (CEN 1147), Sclerotium rolfsii (CEN 216), Sclerotium cepivorum (CEN 1357), Rhizoctonia solani] were evaluated. Additionally, a biological control agent [Trichoderma afroharzianum (T-22)] was also studied. Microorganisms were subjected to growth in PDA (Potato-Dextrose-Agar) culture medium enriched with SSB. Biochars, produced at 300 and 500 ºC, were applied at different doses: 0.0 (control), 0.2, 0.4, 0.6, 0.8 and 1.0 (g of SSB/100 ml of PDA). Biochars showed inhibitory effects on the mycelial growth of the different fungi evaluated. It was observed that there is a certain specificity of biochar concentration that must be evaluated for the control of phytopathogens. In most cases, the 0.4 and 0.6% concentrations had a greater inhibitory effect on phytopathogens and did not affect the biological control agent. Therefore, SSB proved to be a promising product for the control of different soilborne phytopathogens.

Direct and residual effect of biochar derived from biosolids on soil phosphorus pools: A four-year field assessment.

Measures to improve the use of phosphorus (P), either by improved efficiency or reuse, are needed worldwide in order to preserve a finite resource and ensure that farmers have access to it. Currently, the rapidly growing global population has generated an increased demand for this mineral. Sustainably disposing for the massive amount of globally produced biosolids and alternative sources of P for agriculture are two major challenges to address. In this scenario, biosolids-derived biochar (BBC) has been presented as a win-win opportunity. However, the BBC-P dynamics in soil over consecutive cropping seasons remain unclear. Direct (first and second cropping season) and residual (third and fourth cropping season) effects of BBC on soil P fractions, P uptake and corn grain yield were assessed. Additionally, the relationships between soil P pools and grain yield were investigated by multivariate and multiple linear regression analysis. In a field experiment, BBC produced at 300 °C (BC 300) and 500 °C (BC 500) were applied to an Oxisol at a rate of 15 t ha-1. Soil total P and its fractions (organic P, inorganic P, and available P) were determined. Phosphorus uptake and corn grain yield were also evaluated. BBC, regardless of pyrolysis temperature, increased soil total P and all P fractions. Moreover, BBC maintained high soil P contents for at least two years after stopping its application. These results suggest that BBC may act as a slow-release P fertilizer. Surprisingly, soil P fractions were unaffected by different pyrolysis temperatures, but BC 300 promoted higher grain yield than BC 500 in the third and fourth cropping seasons. Overall, the results confirmed that under direct application both biochars can replace mineral fertilization for corn production; and when considering the residual effect, BC 300 showed a higher potential to be utilized as a soil amendment for P supply.

Biochar and Trichoderma harzianum for the Control of Macrophomina phaseolina

Abstract This study is based on the importance of biological control methods and the lack of information on the effect of biochar (BCH) from sewage sludge associated or not with Trichoderma harzianum on the control of Macrophomina phaseolina in the bean crop (Phaseolus vulgaris, cv. BRS Estilo). Biochar from sewage sludge, pyrolyzed at 500 ºC and used in low concentration (0.5%), has a direct effect on the in vitro control of M. phaseolina. However, higher BCH concentrations stimulated the growth of the pathogen. In culture medium with or without BCH, T. harzianum (strain 1306) inhibited the mycelial growth of M. phaseolina. The addition of BCH + T. harzianum reduced the deleterious effects caused by M. phaseolina on bean plants. This study demonstrated that joint application of BCH from sewage sludge + T. harzianum considerably increased the fresh and dry mass of bean plants, inoculated or not with M. phaseolina.

Soil microbial biomass and activity in wetlands located in preserved and disturbed environments in the cerrado biome / Biomassa e atividade microbiana do solo em veredas situadas em ambientes conservados e antropizados no bioma cerrado

The veredas (a type of wetlands) are wet ecosystems usually associated with the presence of hydromorphic soils, which often occur in the vicinity of springs and watercourses of the Cerrado region in Brazil. This study aimed to assess microbiological and biochemical soil properties in wetlands (veredas) located in preserved and disturbed environments (in farming and grazing areas) in the Cerrado biome. Soil samples were collected at depths of 0-10 cm and 10-20 cm, along reference lines arranged according to their position in the landscape, in the upper, middle and lower positions of one of the slopes. The total soil organic carbon, microbial biomass carbon and nitrogen (Cmic and Nmic), microbial biomass C:N ratio, microbial quotient, basal respiration, metabolic quotient and fluorescein diacetate (FDA) hydrolytic activities in soil (as total soil heterotrophic enzymatic activity) were determined. The soils of veredas adjacent to agricultural and livestock environments showed changes in their biological properties compared to preserved ecosystems. Increased microbial biomass (Cmic and Nmic) is reported in veredas located nearby grazing areas under intensive and technified management, on the soil surface layer (0-10 cm), especially in the lower slope position, while in agricultural environments, under the same conditions of relief and depth, there is a relative decrease in microbial biomass carbon.

As veredas são ecossistemas úmidos, normalmente associados à presença de solos hidromórficos, que ocorrem com frequência nas proximidades das nascentes e cursos d'água da região do Cerrado. O objetivo deste trabalho foi avaliar atributos microbiológicos e bioquímicos do solo em áreas úmidas (veredas) localizadas em ambientes conservados e antropizados (em áreas agrícolas e pastagens), no bioma Cerrado. Amostras de solo foram coletadas nas profundidades de 0-10 cm e 10-20 cm, ao longo de linhas de referência dispostas, segundo sua posição no relevo, nas posições superior, média e inferior de uma das vertentes. Foram determinados o carbono orgânico total do solo, carbono e nitrogênio da biomassa microbiana (Cmic e Nmic), relação C:N da biomassa microbiana, quociente microbiano, respiração basal, quociente metabólico e atividade enzimática total do solo. Os solos de veredas vizinhas a ambientes agropecuários apresentaram variações em seus atributos biológicos, comparativamente a ecossistemas conservados. Em veredas adjacentes a pastagens sob manejo intensivo tecnificado, na camada superficial do solo (0-10 cm), ocorreu o incremento da biomassa microbiana (Cmic e Nmic), notadamente na posição inferior do relevo, enquanto em ambientes agrícolas, nas mesmas condições de relevo e profundidade, observou-se uma diminuição relativa do carbono da biomassa microbiana.

Frações granulométricas da matéria orgânica em latossolo sob plantio direto com gramineas / Granulometric fractions of organic matter of a latosol under no-till with grasses

O estudo da matéria orgânica do solo e de seus compartimentos visa obter informações a cerca da sua estabilidade e localização na estrutura do solo, bem como sua quantidade e qualidade em sistemas de uso do solo. O objetivo deste trabalho foi avaliar as frações da matéria orgânica em solo sob manejo de plantio direto com gramíneas. O delineamento experimental foi em blocos ao acaso com três repetições e cinco tratamentos (sistemas de cultivos), com medidas repetidas no espaço. Os tratamentos constituíram-se de milho em monocultivo; Brachiaria humidicola; Panicum maximum cv Aruana; milho + Brachiaria humidicola e milho + Panicum maximum cv Aruana. Foram determinados os teores de carbono orgânico total, carbono orgânico particulado e carbono orgânico associado aos minerais do solo nas profundidades de 0-5, 5-10, 10-20 e 20-30 cm. Foram também analisados os acréscimos e reduções dos estoques de carbono nas diferentes frações utilizando-se a área de cerrado como referência. Os resultados demonstraram que os sistemas com consorciação de culturas e forragens ocasionaram efeitos nos diferentes compartimentos da matéria orgânica. Devido ao curto período de condução do plantio direto, as alterações promovidas pelas culturas nas frações da matéria orgânica foram mais expressivas nas camadas superficiais do solo. Sob plantio direto, o milho em monocultivo ou consorciado com Brachiaria humidicola promoveu aumento nos estoques de carbono orgânico total e nas frações COp e COam, tendo o cerrado nativo como referência. Nos demais sistemas, o uso do solo promoveu aumento dos estoques de COT e COam e redução na fração COp.

The study of soil organic matter and its compartments seeks to obtain information about their stability, localization in soil structure as well as their quantity and quality under land use systems. The objective of this study was to evaluate the organic matter fractions in soil under no-till management with grasses. The experimental design was a randomized block, with three replications and five treatments (cropping systems), with repeated measures in space. The treatments consisted of corn; Brachiaria humidicola; Panicum maximum cv Aruana; corn + Brachiaria humidicola, corn + Panicum maximum cv Aruana. The concentrations of total organic carbon, particulate organic carbon and organic carbon associated with minerals were analyzed in the soil at depths 0-5, 5-10, 10-20 and 20-30 cm. Increases and reductions of carbon stocks in organic matter fractions, using the Cerrado as a reference, were also analyzed. The results demonstrated that the systems with intercropping and fodder caused different effects on organic matter pools. Because of the short period of no-till the changes promoted by crops in organic matter fractions were more significant in the soil surface layers. Under no-till, maize only or intercropped with Brachiaria humidicola promoted an increase in total organic carbon and organic carbon fractions, when the native cerrado soil was used as reference. In other systems, land use increased stocks of OCam and TOC, but promoted reduction in POC stocks.

Recuperação de carbono obtida por três métodos em frações da matéria orgânica de latossolo, sob consórcio milho-forrageiras, no cerrado / Carbon recovery obtained by three methods in organic matter fractions of latosol under maize-grass intercropping in the cerrado

A dinâmica da matéria orgânica do solo (MOS) pode ser melhor compreendida após identificadas suas frações lábeis (> 53 µm) e estáveis (< 53 µm). Diante da importância crescente do uso de técnicas de fracionamento físico da MOS, torna-se necessário avaliar se a recuperação de carbono nessas frações é influenciada pelos métodos utilizados para sua determinação. O objetivo deste trabalho foi avaliar os teores de carbono, por três métodos, em diferentes frações da matéria orgânica, num Latossolo Vermelho-Amarelo distrófico sob consórcio milho-forrageiras e em sistema solteiro. Foram determinados os teores de carbono das frações: (i) particulada da matéria orgânica (COP) e naquela (ii) associada aos minerais da matéria orgânica (COM). Determinou-se ainda, o teor de (iii) carbono orgânico total do solo (COT) na matéria orgânica não fracionada. Três métodos de determinação do carbono orgânico do solo foram utilizados: (i) Walkley & Black modificado, (ii) Mebius modificado, e (iii) combustão via seca, em analisador elementar (CHN). Foram utilizadas amostras de solos de três sistemas de manejo dispostos em delineamento em blocos casualizados, com três repetições para determinação do carbono orgânico do solo: (i) milho solteiro; (ii) milho consorciado com capim colonião (Panicum maximum cv. Aruana); e (iii) milho consorciado com braquiária (Brachiaria humidicola). As amostras de solo foram coletadas na profundidade de 0 ­ 5 cm. O método Walkley & Black apresentou menores valores de COT em relação ao CHN nos sistemas de manejo milho/braquiária e milho solteiro, e mostrou valores de COP semelhantes àqueles obtidos pelo CHN nos sistemas de manejo milho solteiro e milho/braquiária. Valores de COT, COP e COM obtidos pela metodologia de Mebius modificado foram semelhantes àqueles obtidos pelo analisador elementar, para todos os sitemas de manejo. O COP, quando avaliado pelas metodologias de Mebius e CHN, mostrou-se significativamente mais sensível às alterações de manejo em relação ao COT e COM.

Soil organic matter alterations can be better understood when it is fractionated for the identification of its labile (> 53 µm) and stable (< 53 µm) fractions. Because of the increasing and important use of soil organic matter fractionation techniques, it becomes necessary to evaluate if the carbon recovery in these fractions is influenced by methods used for its determination. The aim of this work was to evaluate the content of organic carbon in soil organic matter fractions, by three different methods, under maize-grass intercropping and sole maize in a dystrophic Red-Yellow Latosol (Oxisol). The following carbon contents were determined from the fractions: (i) of the particulate soil organic matter (POM) and from that (ii) of mineral-associated soil organic matter (MOC). The content of total organic carbon (TOC) was also determined in the non-fractionated soil organic matter. Three methods for the determination of soil organic carbon were used: (i) Walkley & Black modified, (ii) Mebius modified, and (iii) dry combustion in a CHN elemental analyzer. The experimental design was a randomized block design with three replications. Soil samples were collected from three management systems: (i) sole corn; (ii) maize-Panicum maximum intercropping; and (iii) maize- Brachiaria humidicola intercropping. Soil samples were collected from the depth of 0 ­ 5 cm. Lower TOC were found in the Walkley & Black method in relation to the CHN elemental analyzer, under the management systems sole maize and maize-Panicum maximum intercropping. However, the Walkley & Black method showed similar POM in relation to CHN analyzer method, under the management systems sole maize and maize-Brachiaria humidicola intercropping. TOC, POM and MOC obtained from the Mebius modified method were similar to those obtained from the elemental analyzer, under the three management systems. The POM when evaluated by the Mebius and CHN methods, showed to be more sensible to soil management alterations.