Processes that influence dissolved organic matter in the soil: a review

In tropical regions, climate conditions favor fast decomposition of soil organic matter (SOM), releasing into the soil organic composts in solid, liquid, and gaseous forms with variable compositions. Dissolved organic matter (DOM), a complex mixture of thousands of organic compounds, is only a small fraction of the decomposition products; however, it is highly mobile and reactive to the soil. Therefore, DOM play a key role in soil aggregation (formation of organometallic complexes), energy source for microorganisms, as well as C storage, cycling, and provision of plant-available nutrients. DOM multifunctionality to sustain soil functions and important ecosystem services have raised global scientific interest in studies on DOM fractions. However, previous studies were conducted predominantly under temperate soil conditions in natural ecosystems. Therefore, there is paucity of information on tropical soil conditions under agricultural systems, where DOM turnover is intensified by management practices. This review synthesized information in the literature to identify and discuss the main sources, transformations, and future of DOM in soils. We also discussed the importance of this fraction in C cycling and other soil properties and processes, emphasizing agricultural systems in tropical soils. Gaps and opportunities were identified to guide future studies on DOM in tropical soils

Conversão do cerrado em agricultura no sudoeste da Amazônia: estoques de carbono e fertilidade do solo

Land use change and land management practices can modify soil carbon (C) dynamics and soil fertility. This study evaluated the effect of tillage systems (no-tillage - NT and conventional tillage - CT) on soil C and nutrient stocks in an Oxisol from an Amazonian cerrado following land use change. The study also identified relationships between these stocks and other soil attributes. Carbon, P, K, Ca and Mg stocks, adjusted to the equivalent soil mass in the cerrado (CE), were higher under NT. After adoption of all but one of the NT treatments, C stocks were higher than they were in the other areas we considered. Correlations between C and nutrient stocks showed positive correlations with Ca and Mg under NT due to continuous liming, higher crop residue inputs and lack of soil disturbance, associated with positive correlations with cation exchange capacity (CEC), base saturation and pH. The positive correlation (r = 0.91, p < 0.05) between C stocks and CEC in the CE indicates the important contribution of soil organic matter (SOM) to CEC in tropical soils, although the exchange sites are - under natural conditions - mainly occupied by H and Al. Phosphorus and K stocks showed positive correlations (0.81 and 0.82, respectively) with C stocks in the CE, indicating the direct relationship of P and K with SOM in natural ecosystems. The high spatial variability of P and K fertilizer application may be obscuring these soil nutrient stocks. In this study, the main source of P and K was fertilizer rather than SOM.Mudanças de uso da terra e práticas de manejo modificam a dinâmica do C e a fertilidade do solo. Este estudo avaliou as implicações dos sistemas de cultivo (NT e CT) nos estoques de C e de nutrientes e identificou inter-relações entre estes estoques e outros atributos da fertilidade do solo em Latossolo após a mudança do uso da terra no cerrado amazônico. Os estoques de C e de nutrientes (P, K, Ca e Mg) ajustados pela massa equivalente do solo sob cerrado (CE), foram maiores principalmente sob NT. Após a adoção do NT, exceto em 2NT, os estoques de C foram maiores em relação às demais áreas avaliadas. Correlações entre estoques de C e de nutrientes revelaram algumas correlações positivas com Ca e Mg nas áreas sob NT, devido ao uso continuo de calcário, à maior quantidade de resíduos culturais e ao não revolvimento do solo, associado à correlações positivas com CTC, saturação por bases e pH. A correlação positiva (r = 0,91, p < 0,05) entre estoques de C e CTC em CE indica a importante contribuição da MOS na CTC de solos tropicais, embora os sítios de troca estejam ocupados principalmente por H + Al. Estoques de P e K mostraram correlações positivas com estoques de C em CE (0,81 e 0,82; respectivamente), indicando a alta relação de P e K com a MOS em ecossistemas naturais. A alta variabilidade espacial associada à aplicação de fertilizantes (P e K) no sulco de plantio pode ter mascarado os resultados dos estoques. A principal fonte destes nutrientes para o solo foi o fertilizante aplicado e não a MOS.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FAPES

Soil dissolved organic carbon responses to sugarcane straw removal

Global demand for bioenergy increases interest in biomass-derived fuels, as ethanol from sugarcane straw. However, straw is the main carbon source to soil and its removal reduces C input, affecting active fractions (dissolved organic carbon, DOC) and C storage. To quantify the effects of straw removal on DOC and C stocks, we built lysimeter system using soil (Rhodic Kandiudox) from sugarcane field. We evaluated four soil depths (1, 20, 50 and 100 cm) and four straw removal rates: no removal NR, medium MR, high HR and total TR, leaving 12, 6, 3 and 0 Mg/ha on the soil surface, respectively. After rainfall, drainage water was collected and analysed for DOC content. Soil C stocks were determined after the 17-month. Total DOC released at 1-cm depth amounted to 606, 500, 441 and 157 kg/ha in NR, MR, HR and TR, respectively. Net-DOC suggests straw as the main source of DOC. Most of DOC in NR (50%) was retained within the 1-20 cm layer, resulting in higher C stock (10 Mg/ha) in the topsoil. In HR and MR, DOC retention was higher within 20-50 cm, suggesting differences in DOC composition. DOC in TR was 40% higher at 20 cm than at 1 cm, indicating C losses from topsoil. Low concentrations of DOC were found at 100-cm depth, but representing 30% in TR. Straw removal for bioenergy production is sustainable, but we should leave at least 3 Mg/ha of straw to ensure DOC production and soil C storage, taking account the DOC contribution to key soil functions

Greenhouse Gas Assessment and Strategies to Achieve CO₂ Sequestration in the Brazilian Palm Oil Life Cycle

As the palm oil production is expanding in Brazilian Amazon region, this study aimed to determinate the greenhouse gas (GHG) emissions since the agricultural phase to transportation of crude palm oil (CPO) and then indicate strategies to achieve the CO2 sequestration. The scope of this study comprised since the stage of oil palm seedlings production until the transportation of CPO. Inventory data for the year of 2009 included the agricultural production of fresh fruit bunches (FFB) and the extraction and transportation of CPO. The management of palm oil mill effluent (POME), use of fertilizers, fuels, pesticides, and electricity contributed to 66.5, 17.9, 15.1, 0.4, and 0.1% of the total emissions, respectively. Agricultural phase, CPO extraction, and transportation emitted 32,131, 79,590, and 1,104 t CO2-eq, respectively. The carbon (C) footprint was 0.79 t CO2-eq / t CPO, and the highest GHG emissions were associated to the management of POME. On the other hand, the use of all residues from the mill as fertilizer substitute can minimize the GHG emissions and increase soil C stocks. In addition, the methane (CH4) from POME captured and used for steam or electricity is also a viable alternative to reduce the GHG emissions

Opções de mitigação de gases do efeito estufa na mudança do uso da terra, pecuária e agricultura no Brasil

National inventories of anthropogenic greenhouse gas (GHG) emissions (implementation of the National Communications) are organized according to five main sectors, namely: Energy, Industrial Processes, Agriculture, Land-Use Change and Forestry (LUCF) and Waste. The objective of this study was to review and calculate the potential of greenhouse gas mitigation strategies in Brazil for the Agricultural and LUCF. The first step consisted in an analysis of Brazilian official and unofficial documents related to climate change and mitigation policies. Secondly, business as usual (BAU) and mitigation scenarios were elaborated for the 2010-2020 timeframe, and calculations of the corresponding associated GHG emissions and removals were performed. Additionally, two complementary approaches were used to point out and quantify the main mitigation options: a) following the IPCC 1996 guidelines and b) based on EX-ACT. Brazilian authorities announced that the country will target a reduction in its GHG between 36.1 and 38.9% from projected 2020 levels. This is a positive stand that should also be adopted by other developing countries. To reach this government goal, agriculture and livestock sectors must contribute with an emission reduction of 133 to 166 Mt CO2-eq. This seems to be reachable when confronted to our mitigation option values, which are in between the range of 178.3 to 445 Mt CO2-eq. Government investments on agriculture are necessary to minimize the efforts from the sectors to reach their targets.Inventários nacionais acerca de emissões de gases do efeito estufa (GEE) (refinamentos das Comunicações Nacionais) são organizadas de acordo com cinco principais setores, a saber: Energia, Processos Industriais, Agropecuária, Mudanças do Uso da Terra e Florestas e Tratamento de Resíduos. O objetivo dessa revisão foi calcular o potencial das estratégias de mitigação de GEE no Brasil para agropecuária e mudança de uso da terra e florestas. A primeira etapa consistiu na análise de documentos oficiais e não-oficiais do Brasil relacionados a mudanças climáticas e políticas de mitigação. O cenário atual, sem adoção de ações mitigadoras (BAU), e os cenários de mitigação foram elaborados para o período 2010-2020. Efetuaram-se os cálculos associados às emissões e remoções de GEE. Adicionalmente, duas estratégias foram utilizadas para destacar e quantificar as principais opções de mitigação: a) seguindo metodologia do IPCC 1996 e b) baseando-se no EX-ACT. Autoridades brasileiras anunciaram que o país buscará reduzir sua taxa de emissão de GEE em 36.1 a 38.9% em relação a 2020. Este é um posicionamento positivo que deve ser adotado por outros países em desenvolvimento. Para alcançar essa meta governamental, os setores agricultura e pecuária devem contribuir reduzindo a emissão em 133 a 166 Mt CO2-eq. Tal redução parece ser atingível quando confrontada com os valores do presente trabalho sobre opções de mitigação os quais estão entre 178,3 e 445 Mt CO2-eq. Investimentos governamentais nos setores agrícola, pecuária e silvicultura são necessários para minimizar os esforços para atingir as metas de redução de emissão pelos outros setores do país.CNPqFAPESPCAPES - COFECU

Atributos químicos e qualidade da matéria orgânica do solo em sistemas de colheita de cana-de-açúcar com e sem queima

The objective of this work was to evaluate soil chemical attributes, to quantify soil contents and stocks of C and N, and to evaluate the chemical quality of soil organic matter in sugarcane harvest systems with or without burning. Cultivated sugarcane areas were evaluated with or without burning of the fields at 6 and 12 years after the last renovation of the sugarcane fields. In addition, a native vegetation area and another one cultivated for 19 years without burning were also evaluated. Soil C content in the unburnt areas was higher thanthat of the burnt ones and lower than that of the areas with native vegetation. Carbon stock at the 0.0–0.3-m soil depth in the burnt areas was 22% lower than in the 6-year unburnt area and 43% lower in the 12-year area. The highest humification degrees occurred in the 19-year unburnt area; and the lowest, in the native vegetation area. The cultivated soils showed higher concentration of phenolic and carboxylic groups in humic acids. Soil fertility increases in the unburnt sugarcane areas because of their more humified organic matter and of the higher quantity of carboxylic and phenolic groups.O objetivo deste trabalho foi avaliar atributos químicos do solo, quantificar os teores e os estoques de C e N, e avaliar a qualidade química da matéria orgânica do solo em sistemas de colheita de cana-de-açúcar com ou sem queima da palhada. Áreas cultivadas com cana-de-açúcar foram avaliadas com ou sem queima da palhada, aos 6 e aos 12 anos após a última reforma do canavial. Além disso, também foram avaliadas uma área de vegetação nativa e outra cultivada por 19 anos sem queima. O teor de C no solo das áreas sem queima foi superior ao daquelas queimadas e inferior ao da área com vegetação nativa. O estoque de C a 0,0–0,3 m deprofundidade, na área queimada, foi 22% menor do que o na área sem queima, aos 6 anos, e 43% menor, aos 12 anos. Os maiores graus de humificação ocorreram na área sem queima por 19 anos; e os menores, na área com vegetação nativa. Os solos cultivados apresentaram maior concentração de grupos fenólicos e carboxílicos nos ácidos húmicos. A fertilidade do solo aumenta em áreas de cana-de-açúcar sem queima, em razão da matéria orgânica do solo mais humificada e da maior quantidade de grupamentos carboxílicos e fenólicos

Estoques de carbono e nitrogênio no solo devido a mudança do uso da terra em áreas de cultivo de café em minas gerais

The type of previous land use to the coffee cultivation and the adopted management practices of coffee pruning may affect the dynamics of soil carbon (C) and nitrogen (N). Thus, the aim of this study was to quantify soil C and N stocks in the three main coffee production regions of Minas Gerais State, evaluating different management systems and coffee cultivation time compared to cultivated pastures. For the calculation of C and N stocks, soil samples were collected to determine the content of C and N, in addition to soil density at different depths. Evaluated situations included management of coffee areas with and without pruning, and the type of previous land use to the coffee crop currently in the areas (i.e. pasture or coffee). The results indicated that coffee cultivation under grazing areas along with the adoption of good agricultural practices such as proper management of pruning and good weed control led to the maintenance of soil C and N stocks over time. Through this fact, it is possible to state that coffee cultivation positively affects soil health.O tipo de uso da terra anterior ao plantio de café e o manejo de podas adotado no cafezal podem condicionar a dinâmica do carbono (C) e do nitrogênio (N) no solo. Desta forma, o objetivo neste trabalho foi quantificar os estoques de C e N do solo nas três principais regiões produtoras de café de Minas Gerais, avaliando diferentes sistemas de manejo e cultivo do café em comparação com pastos cultivados. Para o cálculo dos estoques foram coletadas amostras de solo para determinação dos teores de C e N, além da densidade em diferentes profundidades. As avaliações incluem manejo das áreas com e sem podas, e o tipo de uso da terra anterior ao cultivo do café. Os resultados indicam que o cultivo do café sobre áreas de pastagem, com adoção de boas práticas agrícolas como um manejo adequado de podas e bom controle do mato, propicia a manutenção dos estoques de carbono e nitrogênio do solo. Através deste fato pode-se mencionar que a cafeicultura reflete positivamente na saúde do solo

Soil Organic Matter Quality in Jatropha spp. Plantations in Different Edaphoclimatic Conditions

ABSTRACT: The substitution of native vegetation by agricultural ecosystems can change the quantity and quality of soil organic matter (SOM), and the intensity of these changes depends on the soil type, climate, and land use. The objective of this study was to evaluate the quality of organic matter in chronosequences of Jatropha cultivation in contrasting soil and climatic conditions. Soil samples were evaluated at depths of 0.00-0.10, 0.20-0.30, and 0.80-1.00 m in chronosequences located in Planaltina, Distrito Federal (Cerrado-Pasture-Jatropha), Dourados, Mato Grosso do Sul (Atlantic Forest-Corn-Jatropha), and Araripina, Pernambuco (Caatinga-Jatropha). To assess SOM quality, we determined C contents in the SOM fractions, C stocks, the carbon management index (CMI), the SOM humification index (H LIF ), and the C and N concentrations in the microbial biomass. The conversion of native vegetation to agropastoral systems changed the composition of SOM in the biomes evaluated, especially in the surface layers. The CMI and the C and N contents in the microbial biomass were the most responsive to land use changes in all the biomes studied. The pasture improved SOM quality by increasing the CMI (116) and the C content by 8, 21, and 6 % in the organic, mineral, and organomineral fractions, respectively, while maintaining the SOM humification index and the C and N contents in the microbial biomass in the 0-0.10 m layer. The lowest values of C in the SOM fractions, the CMI (52), and C microbial biomass (136 mg kg -1 ) were observed for annual crops. Jatropha cultivation increased C contents in the SOM fractions, C stocks, the CMI, and C and N in the microbial biomass with an increase in cultivation time, which demonstrates the potential of this long-term system for improving SOM quality