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).

No abstract

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