ABSTRACT. This study aimed to evaluate the nutrition of commercial soybean crops in an agricultural frontier region using the diagnosis and recommendation integrated system (DRIS) and compositional nutrient diagnosis (CND) methods, as well as identify sufficiency ranges. The study was performed by collecting leaf samples (third trifoliate leaf without petiole) at flowering from commercial soybean crops in the states of Piauí and Maranhão, Brazil, and evaluating the crop yield by analyzing macro- and micronutrients in the plant tissue of 98 samples. The DRIS and CND methods were applied based on the cataloged data, followed by the generation of norms, analysis of relationships between yield and nutrients (selecting high-yield crops by the cumulative function of the data), generation of sufficiency ranges, and comparison of methods. The relationships obtained by the DRIS and CND indices with the yield and nutrients were significant, indicating that both methods can be employed for the evaluation of leaf nutrients in soybean. The sufficiency ranges from the DRIS and CND methods presented superior nutrient ranges in relation to the values proposed in the literature for macronutrients, except for nitrogen, and greater range amplitudes for micronutrients.

ABSTRACT Agrosilvopastoral systems have been used as sustainable production models that can promote soil organic carbon (SOC) storage. However, there are no simulation studies with the Century model to estimate the SOC accumulation capacity in the long term, analyzing the effects of management and climate change in integrated crop-livestock-forest (ICLF) systems. This study aimed to simulate soil C dynamics in two chronosequences of land-use composed of native vegetation (NV), degraded pasture (DPA) and ICLF system in the Cerrado of Minas Gerais, in addition to designing future scenarios to verify the potential of SOC accumulation through climate change. The results showed that the Century model reliably simulated the SOC stocks in the two chronosequences evaluated. The model predicted an increase in SOC stocks at two sites by converting the DPA system (46.04 and 42.38 Mg ha-1) into ICLF systems (54.94 and 51.71 Mg ha-1). The Century also predicted that a 20 mm decrease in rainfall and a 2 °C increase in temperature in the tropical regions studied could reduce the SOC stocks more expressively in degraded pastures, while agroforestry systems could show a smaller reduction in SOC stocks. In addition, the results showed that replacing degraded pastures into agrosilvopastoral systems, especially in clayey soils, contributes to increasing SOC stocks. Thus, agroforestry systems are potentially viable to maintain the sustainability of agriculture in the face of climate change.

RESUMO Os solos leves possuem maior suscetibilidade ao processo de degradação e necessitam ser explorados de forma conservacionista, evitando assim sua rápida degradação. Objetivou-se com o estudo avaliar as propriedades físico-hídricas de um Argissolo sob plantio direto e integração lavoura-pecuária no Cerrado da região leste do estado do Maranhão. Os manejos avaliados foram uma área sob sistema de plantio direto há quatorze anos (soja/milheto) e três áreas com diferentes históricos de adoção do sistema de integração lavoura-pecuária (ILP) sob plantio direto (soja/milheto), sendo a diferença os tempos de entrada com ILP (2, 4 e 8 anos), além de uma área de cerrado nativo, considerado testemunha. A coleta do solo foi realizada em junho de 2018 nas profundidades de 0,00-0,10; 0,10-0,20; 0,20-0,30; 0,30-0,50 m. Foram coletadas amostras deformadas e indeformadas, para determinação das variáveis: densidade do solo, porosidade, resistência à penetração, curva de retenção e capacidade de água disponível. Os dados foram submetidos ao cálculo das médias e de intervalo de confiança (95 %). A área com histórico recente de integração lavoura-pecuária apresentou melhor densidade, porosidade, resistência a penetração e capacidade de armazenamento e água disponível. O plantio direto há quatorze anos apresenta alta resistência a penetração, menor porosidade e baixa capacidade de armazenamento de água. O sistema integrado (ILP) melhora a qualidade das propriedades físico - hídricas, sendo o sistema com maior capacidade de água disponível para as plantas.

ABSTRACT Light soils are more susceptible to degradation and need to be exploited in a conservational manner, thus avoiding rapid degradation. The objective of this study was to evaluate the physical-hydraulic properties of an Ultisol under no-tillage and crop-livestock integration in the Cerrado of eastern Maranhão state, Brazil. The evaluated managements were one area under no-tillage system for fourteen years (soybean/ millet) and three areas with different histories of adoption of the crop-livestock integration (CLI) system under no-tillage (soybean/millet), with the difference being: times of entry with CLI (2, 4 and 8 years), as well as a native Cerrado area, considered a control. Soil collection was carried out in June 2018 at depths of 0.00-0.10, 0.10-0.20, 0.20-0.30 and 0.30-0.50 m. Disturbed and undisturbed samples were collected to determine the following variables: bulk density, porosity, resistance to penetration, retention curve and available water capacity. Data were subjected to the calculation of means and confidence intervals (95%). The area with a recent history of crop-livestock integration showed better density, porosity, resistance to penetration, water storage capacity and available water. No-tillage for fourteen years leads to high resistance to penetration, less porosity and low water storage capacity. The integrated system (CLI) improves the quality of the physical- hydraulic properties and the values found are similar to those observed in an area under native vegetation.

RESUMO: Os sistemas integrados de produção agropecuária possuem potencial de incrementar a matéria orgânica, com reflexos nas concentrações de carbono e de nitrogênio no solo. O objetivo do trabalho foi avaliar estoques de carbono e nitrogênio e seus compartimentos em um Argissolo Amarelo Distrocoeso típico sob plantio direto e integração lavoura-pecuária no Leste maranhense. Os manejos avaliados foram: sistema de plantio direto em sucessão há 14 anos (soja/milheto), três áreas com diferentes históricos de sucessão com a adoção do sistema integração lavoura-pecuária (ILP), sendo dois, quatro e oito anos, além de uma área de Cerrado nativo. Foram coletadas amostras de solo nas profundidades de 0,00-0,10; 0,10-0,20; 0,20-0,30; 0,30-0,50 metros para análise de teores e estoques totais de carbono (C) e de seus compartimentos (físico e químico), nitrogênio (N) e da biomassa microbiana do solo e respiração basal. Os resultados revelam maior teor e estoque de C e N nas áreas com ILP. A substância húmica predominante foi a humina e maiores concentrações do carbono associado a minerais estiveram presentes na área sob ILP mais recente (dois e quatro anos). A adoção da ILP, mesmo que recente, proporciona incrementos imediatos nas concentrações de C e suas frações em função do emprego de forrageiras. O plantio direto há 14anos e ILP há oito anos são sistemas com maior índice de manejo do C, como, também, apresentam maior atividade biológica do solo, devido à maiores estabilidade destes sistemas.

ABSTRACT: Integrated agricultural production systems have the potential to increase organic matter content, which is reflected in the soil carbon (C) and nitrogen (N) concentrations. Here, we evaluated the C and N stocks and its compartments in a typical distro cohesive yellow Ultisol under the no-till (NT) and crop-livestock integration (CLI) systems, in eastern Maranhão. Five areas with different management strategies were evaluated, more specifically, one area was managed under the NT system in succession for 14 years (soybean/millet), three areas had different CLI system adoption histories (i.e., CLI was adopted 2, 4, or 8 years prior to sample collection); and finally, one area consisted of native Cerrado (savannah) vegetation. Soil samples were collected at depths of 0-0.10, 0.10-0.20, 0.20-0.30, and 0.30-0.50 m,to analyze the content and total stocks of carbon (C) and its compartments (physical and chemical), N content, soil microbial biomass, and basal respiration. Results revealed higher content and stock of C and N in areas with CLI. The principal humic substance reported was humin, and higher concentrations of C associated with minerals were present in areas under more recent CLI adoption (2 and 4 years). We demonstrated that the adoption of CLI, even if recent, leads to immediate increases in the concentrations of C and its fractions as a result of using forage crops. NT for 14 years and CLI for 8 years exhibited higher levels of C management and higher soil biological activity due to the greater stability of these systems.

RESUMO O objetivo deste trabalho foi avaliar a variação no carbono orgânico total e particulado, relação de estratificação de C, e índice de sensibilidade dessas frações da MOS sob resíduos orgânicos em aléias em um sistema agroflorestal, com e sem uso do fogo na Caatinga. Por meio de experimento em parcelas subdivididas com quatro repetições, onde nas parcelas foi avaliado o fator fogo, e nas subparcelas foi avaliado o fator resíduos orgânicos nas aléias, com as variações de gliricídia isolada, gliricídia com bagana de carnaúba, gliricídia com biocomposto e gliricídia, bagana de carnaúba e biocomposto, sob três profundidades. Nas aléias com uso combinado dos resíduos da bagana de carnaúba, gliricídia e biocomposto houve maior conservação tanto do conteúdo de C orgânico particulado quanto do C associado aos minerais. Assim, o manejo agroflorestal em aléias utilizando a combinação dos três resíduos foi eficiente na conservação de uma matéria orgânica lábil e mais estável. Verificou-se também que o carbono orgânico particulado em todas as aléias foi mais sensível às modificações realizadas no manejo do solo em relação ao conteúdo total da MOS, no qual observou-se maiores índices de sensibilidade dessa fração.

ABSTRACT The objective of this work was to evaluate the variation in total and particulate organic carbon contents, carbon vertical stratification, and sensitivity index of organic matter fractions in soils with organic residues arranged in alleys in an agroforestry system, with and without use of fire, in the Caatinga biome, in Brazil. The experiment was conducted in a split-plot arrangement with four replications, with the factor fire in the plots, and the factor organic residues in the subplots. The organic residues used consisted of Gliricidia sepium plants; G. sepium plants and carnauba processing residue; G. sepium plants and bio-compost; and G. sepium plants, carnauba processing residue, and bio-compost, which were evaluated in three soil layers. The alleys with carnauba processing residue, G. sepium plants, and bio-compost presented a better maintenance of particulate, and mineral-associated organic carbon contents. Thus, the agroforestry management in alleys using these three residues was efficient for the maintenance of labile and recalcitrant organic matter compartments. Particulate organic carbon was more sensitive to changes in soil management than total organic matter content, in all alleys, presenting higher sensitivity indexes.

ABSTRACT The implementation of integrated agricultural production systems is considered a promising strategy for sustainable agricultural intensification in Brazil. This study aimed to evaluate the effects of different monoculture and integrated production systems on the microbiological attributes and organic carbon of soil from the Cerrado region in Piauí, Brazil. Soil samples were collected from the 0.0-0.10-m layer in the following systems: no-tillage (PD), pasture (PAS), exclusive eucalyptus cultivation (CEE), integrated livestock-forest system (IPF) and a native Cerrado (CN) area, which was used as reference. Total organic carbon (TOC) and nitrogen (NT) contents, microbial biomass carbon (CMIC), microbial respiration (MR), microbial quotient (qMIC), metabolic quotient (qCO2), as well as the activities of the hydrolysis of fluorescein diacetate (FDA), acid phosphatase, β-glucosidase and urease enzymes were evaluated. High TOC contents were found in the CEE, IPF and PAS systems, and high CMIC and qMIC values were found in the CN and CEE systems. The variables MR, qCO2 and enzymatic activity varied as a function of the management systems. The IPF and CEE systems caused improvements in the soil attributes, with increases in organic carbon and microbial biomass. The IPF integrated production system promoted improvements in the microbiological indicators of soil quality and was considered an environmentally sustainable agricultural production system. The transition from CN to agricultural areas caused changes in the soil microbiological indicators, which were perceived several years after anthropogenic intervention, indicating that even with the adoption of conservation systems, it was not possible to reestablish the soil microbial biomass.

ABSTRACT Establishing sufficiency ranges and critical levels of nutrients are important for a correct evaluation of plant nutrition through leaf diagnosis. This study aimed to propose critical levels and sufficiency ranges of macro and micronutrients based on leaf diagnosis of soybean plants. The database used was generated from 86 samples of the third trifoliate leaf without petiole, collected during the flowering stage from soybean plants of the main cultivars used in the states of Piauí and Maranhão, Northeast region of Brazil. The results of macro and micronutrients and grain yield were used to calculate the critical level by the reduced normal distribution and boundary line methods, the latter was also used to generate the sufficiency ranges. Nutrient levels for 90 % maximum grain yield were considered for the critical level by the reduced normal distribution, and nutrient levels at the upper line of a dispersion diagram were considered for the boundary line method, using the relation between grain yield and nutrient concentration to generate sufficiency ranges for 95 and 99 % maximum grain yields. The critical levels generated by the boundary line method presented a larger number of deficient samples than the reduced normal distribution method, except for boron. The sufficiency ranges generated by the boundary line with 95 % of the maximum grain yield could not diagnose nutrient deficiency, except for copper. The critical levels by the reduced normal distribution and boundary line methods for leaf diagnosis of soybean were 40.2 and 42.1 g kg-1, 3.2 and 3.4 g kg-1, 17.6 and 19.5 g kg-1, 8.7 and 10.3 g kg-1, 4.7 and 4.9 g kg-1, 2.1 and 2.4 g kg-1, 44 and 44 mg kg-1, 5 and 12 mg kg-1, 125 and 145 mg kg-1, 33 and 34 mg kg-1, and 48 and 63 mg kg-1 for N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn, respectively. The critical levels by boundary line showed better distribution for leaf diagnosis for excess, deficiency, and adequate nutrient levels. The sufficiency ranges by the boundary line method for N, P, K, Ca, Mg, S, B, Cu, Fe, Mn, and Zn were 38.6-45.7 g kg-1, 3.1-3.7 g kg-1, 18.3-20.7 g kg-1, 9.4-11.3 g kg-1, 4.4-5.3 g kg-1, 2.1-2.7 g kg-1, 35-53 mg kg-1, 10-14 mg kg-1, 131-159 mg kg-1, 23-46 mg kg-1, and 58-68 mg kg-1, respectively. The reduced normal distribution and boundary line methods allowed the generation of critical levels and sufficiency ranges for leaf diagnosis of soybean. The sufficiency range generated by the boundary line with 95 % maximum grain yield showed no prevalence of diagnosis of nutrient deficiency, except for copper.

A modelagem de agroecossistemas pode contribuir na definição de programas de pesquisa em regiões tropicais e subtropicais, antecipando o processo de obtenção de resultados de pesquisa e auxilar na tomada de decisão, potencializando o desenvolvimento regional e reduzindo os impactos negativos das atividades agropecuárias nas mudanças climáticas globais. Assim, este trabalho tem como propósito o de apresentar uma revisão bibliográfica sobre esse tema analizando as principais tendências e oportunidades de pesquisa em regiões tropicais relacionadas com o uso de modelos de simulação como ferramentas para a avaliação de sistemas de produção agropecuária.

Agricultural systems modeling can contribute to define research programs in both tropical and subtropical regions (as Brazil), and it can accelerate research process and it can be an ancillary to decision making process, potentializing regional development as well reducing negative agricultural systems production impact on climate change. This study aims to present a review of the literature on this topic analyzing the major research challenges and opportunities in tropical regions related with the use of simulation models as tool to evaluate agricultural systems production.

ABSTRACT The aim of this study was to investigate the short- and medium-term effect of biochar on soil microbial properties, organic carbon and nitrogen in an Oxisol from Brazil. The experiment was conducted in a randomized block design consisting of five levels of biochar (0, 2, 4, 8 and 16 Mg∙ha–1) with and without of synthetic fertilizer: 0 and 200 kg.ha–1 of synthetic fertilizer N-P-K (00-20-20). The following soil properties were determined: microbial biomass carbon (MBC) and nitrogen (MBN), microbial respiration (MR), metabolic quotient (qCO2) and microbial quotient (qMIC), total organic carbon (TOC) and nitrogen (TN). The MBC, qCO2 and carbon management index (CMI) were not altered by doses of fertilizer and biochar. The presence of biochar reduced the MBN by 11% and 5% with the application of16 Mg∙ha–1 compared to control in the third and sixth year, respectively. The qMIC was reduced exponentially with the application of biochar, but was within normal limits as a proportion of total organic carbon. There was an increase in TOC and TN with the application of biochar. The use of biochar did not cause significant negative changes in soil microbial properties or contribute to carbon sequestration in the soil.

Os organismos que constituem a fauna do solo são de grande relevância para os compartimentos serapilheira-solo, por atuarem em importantes processos, como fragmentação do material vegetal, decomposição e ciclagem de nutrientes. Este estudo objetivou avaliar a comunidade da fauna invertebrada do solo sob o cultivo de cana-de-açúcar colhida sem queima, considerando-se a deposição de diferentes quantidades de palhada sobre o solo. Os tratamentos consistiram de diferentes quantidades de palhada de cana-de-açúcar: T0% (0 Mg ha-1); T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">25% (2,2 Mg ha-1); T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">50% (5,1 Mg ha-1); T <img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">75% (7,8 Mg ha-1); e T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">100% (12,0 Mg ha-1). A amostragem aconteceu no período seco e final do período chuvoso, com armadinhas "Pitfall". O número de indivíduos por armadilha ao dia, no período seco, variou entre 11,1 (T0%) e 14,7 (T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">25%) e, no período chuvoso, de 15,11 (T0%) a 33,15 (T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">75%). Os maiores valores de Shannon foram observados no período chuvoso, e os menores valores de diversidade e equitabilidade resultaram da maior incidência dos grupos Araneae e Formicidae. A quantidade de palhada sobre o solo não proporcionou grande influência nos índices ecológicos e riquezas total e média. A época da coleta influenciou na variação do número de indivíduos, riqueza de espécies, índice de Shannon e de Pielou. Amanutenção da palhada promoveu benefícios para a fauna do solo, em relação ao manejo tradicional.

The organisms that constitute the soil fauna are highly relevant to the litter-soil compartments, because they act in important processes, such as fragmentation of the plant material, decomposition and nutrients cycling. This study aimed to evaluate the invertebrate fauna community in soil cultivated with sugarcane harvested without burning, considering the maintenance of different straw levels on the soil surface. Treatments consisted of different amounts of sugarcane straw: T0% (0 Mg ha-1); T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">25% (2.2 Mg ha-1); T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">50% (5.1 Mg ha-1); T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">75% (7.8 Mg ha-1); and T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">100% (12.0 Mg ha-1). Samples were collected in the dry season and late wet season, with "Pitfall" traps. The number of individuals per trap per day during the dry period ranged from 11.1 (T0%) to 14.7 (T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">25%) and, in the rainy season, from 15.11 (T0%) to 33.15 (T<img border=0 width=32 height=32 src="../../../../../../img/revistas/pat/v44n4/a02car01.jpg">75%). The highest Shannon values were observed during the rainy season, and the lowest values for diversity and equitability resulted in a higher incidence of Araneae and Formicidae groups. The amount of straw on soil showed no significant influence on ecological indices and total and average wealth. The harvest time affected the number of individuals, species wealth and Shannon and Pielou's indices. The maintenance of straw on the soil surface benefitted the soil fauna, concerning the conventional crop management.

Este estudo teve como objetivo quantificar os estoques de carbono orgânico total e de suas frações em um argissolo sob sistemas agroflorestais com 6 (SAF6) e 13 anos de idade (SAF13), agricultura de corte-e-queima (ACQ) e floresta nativa de Cerrado (FNC) no Nordeste do Brasil. As amostras de solo foram coletadas nas estações seca e chuvosa, nas camadas de 0-0,05 m; 0,05-0,10 m; 0,10-0,20 m; e 0,20-0,40 m, para avaliar os estoques de carbono orgânico total (COT) e os teores de carbono lábil (CL), fração ácido fúlvico (C-FAF), fração ácido húmico (C-FAH) e humina (C-FH) e carbono da biomassa microbiana (Cmic). Além disso, o índice de manejo de carbono (IMC) foi determinado. Maiores estoques de COT (97,7 e 81,8 Mg ha-1 para 0-0,40 m de profundidade, nas estações seca e chuvosa, respectivamente) e teores de CL, substâncias húmicas e Cmic foram observados no SAF13 em todas as camadas. O IMC também foi maior no SAF13 (0-0,5 m: 158 e 86, 0,05-0,10 m: 171 e 67, respectivamente, nas estações seca e chuvosa), especialmente quando comparado com ACQ (0-0,05 m: 5,6 e 5,4; 0,05 -0,10 m: 5,3 e 5,8, respectivamente, nas estações seca e chuvosa). Os sistemas agroflorestais aumentam a qualidade do solo por meio da conservação da matéria orgânica e podem ser considerados como excelente estratégia para a garantia da sustentabilidade em solo tropical do Nordeste brasileiro.

This study aimed at quantifying total organic carbon stocks and its pools in Acrisol under agroforestry systems with six (AFS6) and thirteen years old (AFS13), slash-and-burn agriculture (SBA) and savanna native forest (SNF) in northeastern Brazil. Soil samples were collected at 0-0.05 m, 0.05-0.10 m, 0.10-0.20 m and 0.20-0.40 m depths in the dry and rainy seasons to evaluate total organic carbon (TOC) stocks and labile carbon (LC), fulvic acid fraction (C-FAF), humic acid fraction (C-HAF), humin (C-HF) and microbial biomass carbon (Cmic) contents. Additionally, carbon management index (CMI) was determined. Higher TOC stocks (97.7 and 81.8 Mg ha-1 for the 0-0.40 m depth in the dry and rainy seasons, respectively) and LC, humic substances and Cmic contents were observed in the AFS13 in all the depths. CMI also was higher in the AFS13 (0-0. 05 m: 158 and 86; 0.05-0.10 m: 171 and 67, respectively for the dry and rainy seasons) especially when compared to the SBA (0-0.05 m: 5.6 and 5.4; 0.05-0.10 m: 5.3 and 5.8, respectively for dry and rainy seasons). The agroforestry systems increased soil quality through the conservation of organic matter and can be considered an excellent strategy to assurance sustainability in tropical soil of Northeastern Brazil

O objetivo deste trabalho foi determinar os efeitos de sistemas de manejo do solo sobre os estoques e as frações de carbono orgânico de um Latossolo Amarelo, no cerrado do Piauí. Foram avaliados os sistemas: plantio convencional por três anos; plantio direto por três e cinco anos, com uso de milheto como cultivo de cobertura; e plantio direto por nove anos, dos quais sete com uso de milheto e dois com forrageira (Urochloa brizantha). Utilizou-se área de cerrado nativo como referência. Amostras de solo foram coletadas nos períodos chuvoso e seco, das camadas de 0,00-0,05, 0,05-0,10, 0,10-0,20 e 0,20-0,40 m, para determinação de: estoques e totais de carbono orgânico e nitrogênio; teores de substâncias húmicas; e índice de humificação. Na camada de 0,00-0,05 m, em ambos os períodos, foram observados os maiores teores de carbono no solo sob cerrado. No entanto, nos dois períodos e nas quatro profundidades, verificaram-se os maiores estoques de carbono e nitrogênio bem como os maiores teores de substâncias húmicas nos solos sob plantio direto por cinco e nove anos. Os maiores índices de humificação também foram observados nesses solos, no período seco. O plantio direto, associado ao uso de cultivos de cobertura, diminui a mineralização da matéria orgânica do solo, estoca carbono no solo em profundidade e favorece o sequestro de carbono em áreas do cerrado do Piauí.

The objective of this work was to determine the effects of soil management systems on the stocks and fractions of organic carbon of an Oxisol (Xantic Ferralsol), in the cerrado of the state of Piauí, Brazil. The following systems were evaluated: a three‑year‑old conventional tillage; a three‑ and a five‑year‑old no‑tillage system, using millet as cover crop; and a nine‑year‑old no‑tillage, using millet as cover crop for seven and forage (Urochloa brizantha) for two years. A native cerrado area was used as a reference. Soil samples were collected in the wet and dry seasons from 0.00-0.05, 0.05-0.10, 0.10-0.20, and 0.20-0.40 m depths for determining: total organic carbon and nitrogen contents and stocks; humic substances content; and humification index. The highest carbon contents were observed in the soil under cerrado, at 0.00-0.05 m depth, in both seasons. However, the highest stocks of carbon and nitrogen as well as the highest contents of humic substances were verified in the soil with no‑tillage system for five and nine years, in both seasons, at all evaluated depths. The highest humification index was also observed in these soils, in the dry season. No‑tillage associated with cover crops decreases soil organic matter mineralization, increases soil carbon stocks in depth, and favors carbon sequestration in cerrado areas of Piauí state.

Insight of nutrient release patterns associated with the decomposition of plant residues is important for their effective use as a green manure in food production systems. Thus, this study aimed to evaluate the ability of the Century, APSIM and NDICEA simulation models for predicting the decomposition and N mineralization of crop residues in the tropical Atlantic forest biome, Brazil. The simulation models were calibrated based on actual decomposition and N mineralization rates of three types of crop residues with different chemical and biochemical composition. The models were also validated for different pedo-climatic conditions and crop residues conditions. In general, the accuracy of decomposition and N mineralization improved after calibration. Overall RMSE values for the decomposition and N mineralization of the crop materials varied from 7.4 to 64.6% before models calibration compared to 3.7 to 16.3 % after calibration. Therefore, adequate calibration of the models is indispensable for use them under humid tropical conditions. The NDICEA model generally outperformed the other models. However, the decomposition and N mineralization was not very accurate during the first 30 days of incubation, especially for easily decomposable crop residues. An additional model variable may be required to capture initial microbiological growth as affected by the moisture dynamics of the residues, as is the case in surface residues decomposition models.

O objetivo desse trabalho foi avaliar a distribuição da fauna em função da umidade do solo em diferentes sistemas de manejo para a produção de forragens com capim-Tifton 85 (Cynodon dactylon Pers. x C. niemfuensis Vanderys), capim-Tanzânia (Panicum maximum Jacq. cv. Tanzânia), capim-Andropogon (Andropogon gayanus Kunth), Leucena (Leucaena leucocephala (Lam.) R. de Wit.) tendo como controle uma Mata dos Cocais. A coleta da fauna foi feita utilizando-se armadilhas do tipo Pitfall em duas épocas do ano: setembro de 2007 e março de 2008, período seco e chuvoso, respectivamente. Os sistemas com capim-Tifton, capim-Tanzânia e Leucena mostraram maior número de indivíduos nos dois períodos avaliados. A queimada ocorrida no capim-Andropogon antes da primeira coleta resultou em uma redução na abundância e diversidade da fauna edáfica. Os maiores valores em riqueza, diversidade e uniformidade de fauna foram obtidos na amostragem realizada no período úmido. A mata mostrou maior diversidade e equitabilidade nos dois períodos avaliados. Em situação de estresse hídrico alguns grupos como Formicidae e Collembola predominaram nos sistemas de manejo diminuindo a uniformidade, enquanto no período úmido vários grupos mostraram boa representatividade o que favoreceu a uniformidade. A análise multivariada de componentes principais evidenciou que os sistemas com mata, capim-Tifton e capim-Tanzania e Leucena mostraram associação com vários grupos da fauna edáfica nos dois períodos avaliados enquanto que o sistema com capim-Andropogon, que sofreu queimada, apresentou afinidade apenas com o grupo Heteroptera, no período seco.

The objective of this study was to evaluate the distribution of fauna as a function of soil moisture in different fodder-production management systems of Tifton 85 grass (Cynodon dactylon Pers. x C. niemfuensis Vanderys), Tanzania grass (Panicum maximum Jacq. cv. Tanzânia), Andropogon Grass (Andropogon gayanus Kunth) and Leucena plants (Leucaena leucocephala (Lam.) R. de Wit.), with a coca-crop forest used as control. Sampling of the fauna was accomplished using "pitfall" traps in two periods of the year: September 2007 and March 2008, the dry and wet seasons respectively. Those systems with Tifton grass, Tanzania grass and Leucaena plants showed a higher number of individuals in both periods. The fire which occurred in the Andropogon grass before the first harvest resulted in a reduction in the amount and diversity of the soil fauna. The highest values for wealth, diversity and uniformity of fauna, were obtained from samples collected during the wet season. The forest presented a greater diversity and balance for both periods assessed. In a situation of water-stress, some groups, such as Collembola and Formicidae, predominated in the management systems, decreasing uniformity, while in the wet season, several groups were well represented, favouring uniformity. Principal-component multivariate analysis showed that systems of forest, Tifton grass, Tanzania grass and Leucaena plants were associated with several groups of soil fauna in the two periods evaluated, while the system of Andropogon grass, which suffered a fire, showed an affinity only with the Hepteroptera group during the dry season.

O objetivo deste trabalho foi avaliar os atributos químicos de um Latossolo Amarelo sob diferentes sistemas de manejo do solo, no cerrado piauiense. Foram avaliados quatro sistemas de manejo: plantio convencional por três anos; plantio direto por três anos (PD3) e cinco anos (PD5), com uso de milheto como cultivo de cobertura; e plantio direto por nove anos (PD9), dos quais sete com uso de milheto e dois com forrageira. Utilizou-se área de cerrado nativo como referência. As amostras do solo foram coletadas em períodos chuvosos e secos, nas camadas 0,00-0,05, 0,05-0,10, 0,10-0,20 e 0,20-0,40 m, para determinação de pH, Al3+, H+Al, Ca2+, Mg2+, K+, P disponível, carbono orgânico total (COT), soma de bases (SB), capacidade de troca de cátions efetiva (t) e potencial (T), e saturação por bases (V) e por alumínio (m%). O sistema PD9 apresentou maiores valores de pH e menores de Al3+, H+Al e m%. Observaram-se maiores valores de Ca2+, K+, SB, t, T, V e P sob PD5 e PD9, até 0,20 m. Os maiores valores de COT foram verificados sob PD5 e PD9, exceto na camada de 0,00-0,05 m. O acúmulo de material orgânico associado ao uso de forrageira em PD favorece o aumento dos teores de COT nas camadas mais profundas do solo, no período seco.

The objective of this work was to evaluate the chemical attributes in a Xanthic Ferralsol under different tillage systems in the cerrado of Piauí State, Brazil. Four tillage systems were evaluated: three-year-old conventional tillage; no-tillage with three (NT3) and five years old (NT5), using millet as cover crop; and no-tillage with nine years old (NT9), of which seven years used millet as cover crop and two used forage. A native cerrado area was taken as reference. Soil samples were collected in wet and dry seasons at soil depths, 0.00-0.05, 0.05-0.10, 0.10-0.20 and 0.20-0.40 m, and analyzed for pH, Al3 +, H + Al, Ca2 +, Mg2+, K+, sum of bases (SB), effective (t) and potential (T) cation exchangeable capacity, base (BS) and Al3+ saturation (m%), available P and total organic carbon (TOC). The system NT9 showed the highest values of pH and lowest of Al3+, H+Al, and m%. The highest values for Ca2+, K, SB, t, T, V% and P, were observed under NT5 and NT9, until 0.20 m depth. The highest TOC contents were verified also under NT5 and NT9, except for 0.00-0.05 m soil depth. Organic matter accumulation associated with pasture under no-till increases TOC content at deeper soil layers in the dry period.