The present study describes the preparation and characterization of a novel urea slow-release nanocomposite, based on urea intercalation into montmorillonite clay by an extrusion process at room temperature. Nanocomposites with urea contents ranging from 50 to 80 wt % were successfully produced and characterized. Analyses by XRD, DTA, and SEM-EDX confirmed the effectiveness of this simple process to exfoliate the clay lamellae into the urea matrix, forming a product that can be classified as a nanocomposite, due to the exfoliation degree attained. Diametral compression tests showed that the samples were very deformable, and the release rate of active components in water showed that the nanocomposite showed a slow release behavior for urea dissolution, even in low montmorillonite amounts (20% in weight).

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Knowledge of the spatial variability of soil properties and of forage yield is needed for informed use of soil inputs such as variable rate technology (VRT) for lime and fertilizers. The objective of this research was to map and evaluate the spatial variability of soil properties, yield, lime and fertilizer needs and economic return of an alfalfa pasture. The study was conducted in a 5.3 ha irrigated alfalfa pasture in Sao Carlos, SP, Brazil that was directly grazed and intensively managed in a 270-paddock rotational system. Alfalfa shoot dry matter yield was evaluated before grazing. Soil samples were collected at 0-0.2 m depth, and each sample represented a group of 2 or 3 paddocks. Apparent soil electrical conductivity (ECa) was measured with a contact sensor. The cost of producing 1 ha of alfalfa was estimated from the amount of lime and fertilizer needed and was then used to estimate the total cost of production for the dairy system. The alfalfa dry matter yield was used to simulate the pasture stocking rate, milk yield, gross revenue and net profit. The spatial variability of soil properties and site-specific liming and fertilizer needs were modeled using semi-variograms with VESPER software, the soil fertility information and economic return were modeled with SPRING software. The results showed that geostatistics and GIS were effective tools for revealing soil and pasture spatial variability and supporting management strategies. Soil nutrients were used to classify the soil spatial distribution map and design site-specific lime and fertilizer application maps. Spatial variation in forage and spatial estimates of stocking and milk yield are adequate pasture management tools. Spatial analyses of needs, forage availability and economic return are management tools for avoiding economic problems, as well as potential environmental problems, caused by unbalanced nutrient supplies and over-or under-grazing.

The rapid hydrolysis of urea applied to the soil surface causes high rates of NH3 volatilization, leading to adverse environmental impacts and decreased uptake of N by crops. One approach that can be used to improve the efficiency of urea use involves strategies to control its release, such as the coating of granules with polymers. However, the effectiveness of this method can be limited by poor interaction between the coating and the granule surface. We, therefore, propose a novel class of nanocomposite fertilizers, based on clay exfoliation in urea matrices, with or without polymerization using formaldehyde as a strategy to increase the interaction between urea and the additives. A comparative study was performed using various slow-release fertilizers, determining the amounts of volatilized ammonia, dry matter production, and efficiency of urea-N uptake by ryegrass, in a trial carried out in a greenhouse. Interaction, such as solubility, thickness, and chemical composition of the composites revealed aspects of the interaction that affected the slow-release behavior of urea in soil and the availability of N for plants. It could be concluded that the controlled release of urea from the nanocomposites decreased NH3 volatilization, resulting in a more constant N availability in the soil and better synchronization with the nutritional demands of the plants. The new fertilizers offer a practical option for increasing urea-N efficiency, reducing environmental impacts caused by NH3 loss and improving the quality of forage grown on low fertility soils, such as oxisols.

RESUMO SUMMARY: ESTIMATION OF POTENTIAL ACIDITY BY pH SMP IN SOILS FROM NORTHEASTERN BRAZIL In this study the relationship between the pH SMP and H + Al concentrations was evaluated, in order to establish an equation for estimating the potential acidity of soils from

RESUMOO presente trabalho objetivou aplicar os conceitos de geoestatística e geoprocessamento para a obtenção de zonas de manejo de uma área de pastagem de capim Tanzânia, em São Carlos -SP, e delimitação de unidades de manejo para aplicação de calagem e adubação, com base no melhor método de interpolação. Com os resultados de análise de solo foram realizadas análises geoestatísticas para avaliação da dependência espacial dos atributos químicos. Os mapas foram obtidos pelo método de interpolação por Krigagem Ordinária e a definição das zonas de manejo foi realizada por meio de lógica fuzzy. A partir dos mapas dos parâmetros químico do solo gerou-se o mapa de zonas de manejo resultando em cinco zonas sendo: 0,02ha (1,2% da área total) consideradas como "muito baixa" fertilidade; 0,3ha (18%) "baixa" fertilidade; 0,75ha (44%) como "média" fertilidade; 0,55ha (32%) como "alta" fertilidade e, 0,08ha (4,8%) como "muita alta" fertilidade. A comparação dos métodos de interpolação demonstrou que a Krigagem Ordinária foi a melhor metodologia para o estudo. A geoestatística e o geoprocessamento demonstraram ser técnicas que auxiliam nas decisões estratégicas e complexas em relação ao gerenciamento do sistema de produção agrícola. Palavras-chave: agricultura de precisão, zonas de manejo, métodos de interpolação GEOSTATISTICS AND GIS IN THE DECISION MAKING OF THE USE OF INPUTS IN A PASTURE ABSTRACTThe present study aimed to apply the concepts of geostatistics and GIS to obtain management zones of a pasture Tanzania grass in São Carlos -SP/Brazil, and delimitation of management units for the application of liming and fertilization, based on the best interpolation method. Geostatistical analysis were performed based on results of soil analysis in order to evaluate the spatial dependence of the chemical attributes. The maps were obtained by Ordinary Kriging interpolation method and the definition of management zones was performed by fuzzy logic. From the maps of chemical parameters of the soil has resulted from the management zone map, resulting in five areas being: 0.02 ha (1.2% of total area) regarded as "very low" fertility; and 0.3 ha (18%) "low" fertility; 0.75 ha (44%) as "average" fertility; 0.55 ha (32%) * karoline.eduarda@usp.br

RESUMO:Arroz e feijão foram cultivados em soluções nutritivas em presença de três níveis de N, P e K. O método da bioavaliação do estado nutricional em que raízes destacadas absorvem elementos marcados, no caso presente 15 N e 32 P, foi comparado com o de diagnose foliar. Foram tiradas duas conclusões principais: 1) os bioensaios mostraram ser um procedimento rápido e útil para o diagnóstico do estado nutricional das duas espécies, visto haver correlação significativa negativa entre absorção e produção de matéria seca; 2) a absorção de dois isótopos pelas raízes da planta previamente submetida a níveis diferentes de N e de P na solução foi inversamente proporcional aos teores foliares desses elementos. Descritores: estado nutricional, bioavaliação, arroz, feijão, P, was compared with foliar analysis. Two main conclusions were drawn: 1) the bioevaluation proved to be an useful and rapid procedure for the diagnosis of the nutricional status of both species, since there was a significant negative correlation between absorption of N and P and dry matter yield; 2) the uptake of the tagged ions with either element by the roots of plants grown under deficient levels of N and P in the nutrient solution was inversely proportional to the leaf concentration of both nutrients. Key Words: nutricional status, bioevaluation, rice, bean, 15 N, 32 P. INTRODUÇÃOAvaliar o estado nutricional de uma planta significa comparar a amostra (aspecto ou composição) com um padrão. Padrão, por sua vez, quer dizer planta ou parte dela em que todos os macro e micronutrientes aparecem em concentrações e proporções associadas com alta produtividade (MALAVOLTA et al., 1989).Os dois métodos mais utilizados para esse tipo de comparação são a diagnose visual e a diagnose foliar. A bioavaliação do estado nutricional se baseia no princípio de que, as plantas tem uma capacidade limitada de absorver elementos do meio em que estão suas raízes. Por esse motivo, plantas bem nutridas que já absorveram um dado elemento, quando colocados na sua presença absorverão quantidades menores que os indivíduos desnutridos e com concentrações mais baixas do elemento nos seus tecidos. Em outras palavras, dentro de limites e num período determinado, há uma relação inversa entre estado iônico interno e absorção. O ensinamento tem quase 60 anos: HOAGLAND & BROYER (1936) usavam raízes das plantas "low salt, high carbohydrate" em seus estudos de absorção iônica, visto que elas eram capazes de absorver quantidades maiores do elemento em estudo durante o período experimental.

Knowledge on spatial variability of soil properties is useful for the rational use of inputs, as in the site specific application of lime and fertilizer. Crop-livestock-forest integrated systems (CLFIS) provide a strategy of sustainable agricultural production which integrates annual crops, trees and livestock activities on a same area and in the same season. Since the lime and fertilizer are key factors for the intensification of agricultural systems in acid-soil in the tropics, precision agriculture (PA) is the tool to improve the efficiency of use of these issues. The objective of this research was to map and evaluate the spatial variability of soil properties, liming and fertilizer need of a CLFIS. The field study was carried out in a 30 ha area at Embrapa Pecuária Sudeste in São Carlos, SP, Brazil. Soil samples were collected at 0–0.2 m depth, and each sample represented a paddock. The spatial variability of soil properties and site-specific liming and fertilizer needs were modeled using semi-variograms, the soil fertility information were modeled. Spatial variability soil properties and site specific liming and fertilizer need were modeled by kriging and inverse distance weighting (IDW) techniques. Another approach used was based on lime and fertilizer recommendation considering the paddocks as the minimum management unit. The results showed that geostatistics and GIS were useful tools for revealing soil spatial variability and supporting management strategies. Soil nutrients were used to classify the soil spatial distribution map and design site-specific lime and fertilizer application zones. Spatial analyses of crop needs and requirement can provide management tools for avoiding potential environmental problems, caused by unbalanced nutrient supplies.