O objetivo deste trabalho foi avaliar o estoque de carbono orgânico total (COT) e nitrogênio total (NT), C e N nas frações lábeis e recalcitrantes da matéria orgânica do solo (MOS) e o índice de manejo de C, em solos sob sistema de integração lavoura-pecuária (ILP), após quatro (ILP4) e oito anos (ILP8) de implantação. Para comparação, foram utilizados outros sistemas de manejo: pastagem e lavoura em plantio direto (PD), além de vegetação nativa. O experimento foi realizado em delineamento inteiramente casualizado, com cinco repetições. A integração lavoura-pecuária, estabelecida num período de oito anos, é capaz de alcançar um novo estado estável equivalente ao sistema sob plantio direto com 23 anos de implantação. Houve acúmulo no estoque de C total de 101,0 (ILP8) e 104,2 Mg ha-1 (PD) e N total de 5,5 (ILP8) e 5,8 Mg ha-1 (PD), na camada 0-30 cm, bem como aumento no estoque de C e N nas frações lábeis e recalcitrantes da MOS. Para o ILP com oito anos, o índice de manejo de C de 88 foi superior ao dos demais sistemas de manejo e não diferiu da vegetação nativa na camada 0-10 cm, todavia, foi similar ao PD na análise de todo o perfil (0-30 cm).

This work summarizes information about organic nitrogen (N) in the agricultural system. The organic N forms in soils have been studied by identifying and quantifying the released organic compounds when soils are acid treated at high temperature, in which the following organic N fractions are obtained: hydrolyzable total N, subdivided into hydrolyzable NH4+-N, amino sugars-N, amino acids-N, and unidentified-N and acid insoluble N, a fraction that remains associated with soil minerals after acid hydrolysis. Nitrogen mineralization and immobilization are biochemical processes in nature. This chapter summarizes how these processes occur in the agricultural system. Then, soluble organic nitrogen (SON), volatilization and denitrification processes, and biological nitrogen fixation (BNF) as a key component of the nitrogen cycle and how it makes N available to plants are also discussed. Finally, we discuss the use of organic fertilizers as N source to satisfy the worldwide demand for organic foods produced without synthetic inputs.

Mineralogical studies are incipient and necessary in the Apodi Plateau, Brazil. This study aimed to evaluate the interrelationship between the mineralogy of the clay fraction and its structural and chemical attributes and to differentiate two important pedo-environments in the semi-arid region of northeastern Brazil (Ferralsol and Cambisols of the Apodi Plateau-RN) using the multivariate technique. We evaluated the interrelationships between mineralogy and the structural and chemical attributes of the soil and differentiated between agroenvironments. We collected soil samples from six profiles in diagnostic horizons of the Ferralsols and Cambisols. In the mineralogical analysis of the clay fraction, X-Ray Diffraction was used to identify mineral peaks of clay and iron oxides. The physical and chemical properties of the soils were determined. The multivariate statistical technique was applied to process the data. The clay minerals identified were hematite, goethite, kaolinite, and illite. The principal component analysis allowed for the separation of environments according to soil density, Fed and Mg²⁺ for developed soils, and potassium, weighted average diameter, microporosity, total organic carbon, sodium, the sum of bases, calcium, total porosity, aeration, potential acidity, and Feo discriminated developing soils. This study revealed that the clay fraction influenced the structural attributes of the soil according to the degree of soil development. Two profiles presented atypical situations: High contents of crystallized iron in Cambisols and illite peaks in Ferralsolos. These mineralogical results are not commonly found in the literature, highlighting the potential for further studies. The answers concerning the mineralogy of semiarid soils in Brazil and the world show similarity.

Aim i) is there a difference in the level of contamination in the different parts of the basin in the water, sediment and aquatic macrophytes compartments? and ii) do the three compartments respond similarly to metal contamination? Methods Samples of water, sediment and aquatic macrophytes (Salvinia auriculata Aubl., Pistia stratiotes L., Ludwigia helminthorrhiza (Mart.) H. Hara and Eichhornia crassipes (Mart.) Solms) were collected at 10 sampling sites in different stretches of a tropical hydrographic basin. We determined the metal concentrations of Fe, Pb, Ni, Zn, Mn, Cr, Cu and Cd, and to the results we applied Principal Component Analysis (PCA), separately for each compartment, to order the sampling sites. Results Fe and Mn had higher concentrations than other metals in plants and sediment. With the exception of Mn, the order of metals was similar between water and sediment. However, the PCAs ordered the sampling sites differently. Our results demonstrated that the ordering of sampling sites by metal concentrations differs among water, sediment and macrophytes. Conclusions We conclude that to evaluate the contamination of aquatic environments by metals and the effects of contamination on the food chain, it is not enough to evaluate them only in water or sediment, but also in an aquatic community.

The deposition of organic residues through mechanical harvesting of cane sugar is a growing practice in sugarcane production system. The maintenance of these residues on the soil surface depends mainly on environmental conditions. Nitrogen fertilization on dry residues tend to retard decomposition of these, providing benefits such as increased SOM. Thus, the object of this research was to evaluate the effect of different doses of nitrogen on sugar cane crop residues, as its decomposition and contribution to carbon sequestration in soil. The experiment was conducted in Dourados-MS and consisted of a randomized complete block design. Dried residues were placed in litter bags and the treatments were arranged in a split plot, being the four nitrogen rates (0, 50, 100 and 150 kg ha-1 N) the plots, and the seven sampling times (0, 30, 60, 90, 120, 150 and 180) the spit plots. Decomposition rates of residues, total organic carbon and labile carbon on soil were analysed. The application of increasing N doses resulted in an increase in their decomposition rates. Despite this, note also the mineral N application as a strategy to get higher levels of labile carbon in soil.A deposição de resíduos orgânicos através da colheita mecanizada da cana-de-açúcar é uma prática crescente no sistema de produção canavieiro. A manutenção desses resíduos na superfície do solo depende principalmente das condições ambientais. A adubação nitrogenada sobre os resíduos secos tendem a retardar a decomposição desses, proporcionando benefícios como o aumento da MOS. Diante disto, o objetivo da pesquisa foi avaliar o efeito da aplicação de diferentes doses de nitrogênio sobre os resíduos culturais de cana-de-açúcar, quanto a sua decomposição e contribuição para o sequestro de carbono no solo. O experimento foi realizado em Dourados-MS e consistiu de um delineamento experimental em blocos casualizados. Os resíduos secos foram colocados em litter bags e os tratamentos foram arranjados em parcelas subdivididas, sendo as quatro doses de nitrogênio (0,50, 100 e 150 kg ha-1 N) as parcelas, e as sete épocas de coleta (0, 30, 60, 90, 120, 150 e 180 dias) as subparcelas. Foram analisados a taxa de decomposição dos resíduos, carbono orgânico total e carbono lábil no solo. A aplicação de doses crescente de N proporcionou aumento nas suas taxas de decomposição. Apesar disso, destaca-se a aplicação de N-mineral como uma estratégia de manejo para obter maiores teores de carbono lábil no solo

Modern times have required studies that take into account the main soil features, aligning the use of land with the protection of more sensitive environments. From this perspective, this study aimed to perform a morphological description and determine the physical and chemical attributes for soil classification in the community of Poção, located in the municipality of Martins/RN, by highlighting the more sensitive attributes in the differentiation of environments through multivariate analysis. Nine soil profiles were identified to perform the morphological description and collect samples for physical and chemical analyses. The study updates the soil classes found in the study area: Acrisols, Planosols, and Cambisols, with the relief being the main factor responsible for the difference between soil attributes. The influence of organic matter on the soil attributes highlights the importance of its maintenance. Aluminum and the clay fraction are responsible for the distinction of the Acrisol class, whereas silt, potassium sodium, total organic carbon, the electrical conductivity of the saturation extract, and the cation exchange capacity allow the differentiation of Fluvisols.