Developing efficient crop fertilization practices has become more and more important due to the ever-increasing global demand for food production. One approach to improving the efficiency of phosphate and urea fertilization is to improve their interaction through nanocomposites that are able to control the release of urea and P in the soil. Nanocomposites were produced from urea (Ur) or extruded thermoplastic starch/urea (TPSUr) blends as a matrix in which hydroxyapatite particles (Hap) were dispersed at ratios 50% and 20% Hap. Release tests and two incubation experiments were conducted in order to evaluate the role played by nanocomposites in controlling the availability of nitrogen and phosphate in the soil. Tests revealed an interaction between the fertilizer components and the morphological changes in the nanocomposites. TPSUr nanocomposites provided a controlled release of urea and increased the release of phosphorus from Hap in citric acid solution. The TPSUr nanocomposites also had lower NH3 volatilization compared to a control. The interaction resulting from dispersion of Hap within a urea matrix reduced the phosphorus adsorption and provided higher sustained P availability after 4 weeks of incubation in the soil.
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.
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