The preparation and characterization of a controlled-release multicomponent (NPK) fertilizer with the coating layer consisting of a biodegradable copolymer of poly(butylene succinate) and a butylene ester of dilinoleic acid (PBS/DLA) is reported. The morphology and structure of the resulting polymer-coated materials and the thickness of the covering layers were examined using X-ray diffraction and scanning electron microscopy coupled with energy dispersive X-ray analysis. The mechanical properties of these materials were determined with a strength-testing machine. Nutrient release was measured in water using spectrophotometry, potentiometry, and conductivity methods. The results of the nutrient release experiments from these polymer-coated materials were compared with the requirements for controlled-release fertilizers. A conceptual model is presented describing the mechanism of nutrient release from the materials prepared in this study. This model is based on the concentrations of mineral components inside the water-penetrated fertilizer granules, the diffusion properties of the nutrients in water, and a diffusion coefficient through the polymer layer. The experimental kinetic data on nutrient release were interpreted using the sigmoidal model equation developed in this study.

Calcination process was investigated on the laboratory scale with the use of hydrated titanium dioxide containing rutile nuclei from the industrial installation (sulfate process). The influence of temperature (750−900 °C) on the anatase−rutile phase transformation and on the crystallites' growth variation was determined. Phosphate, potassium, lithium, and aluminum were introduced into calcination suspension. It was found that whereas an introduction of lithium, in phosphate presence, either increased or stabilized the anatase−rutile transformation degree, the introduction of potassium significantly decreased it. The intensity of these changes depended on both the temperature of the process and on phosphate content. The introduction of aluminum, in constant phosphate presence, had an intermediate influence on the rutilization of anatase between that of either potassium and phosphate on the one hand and lithium and phosphate on the other. Similarly to potassium, aluminum intensified the influence of phosphate but to a smaller degree and only a lower temperature. The introduction of lithium, regardless of whether or not phosphate and potassium were present, increased rutilization degree. This dependence was more clearly seen at lower temperatures of the process. Aluminum, either in constant phosphate and potassium or phosphate and lithium presence, increased the anatase−rutile transformation. The degree of these changes depended on both the presence of modifying agents in their mixture and on the temperature of the process. It was found that the introduction to hydrated titanium dioxide of additives causing an increase in the surface area of TiO2, as a result of limitations of crystallite growth in the calcination process, results in elevation of temperature of the anatase−rutile phase transformation (phosphates, potassium) whereas the introduction of additives that decrease the surface area (crystallite growth) enhances the degree of transformation of anatase to rutile (lithium).

Biodegradable chitosan was used to cover fertilizer granules with an inert, impermeable layer in order to obtain a material with controlled release properties. The process was performed in a laboratory drum granulator. Prepared materials were characterized with available analytical methods (XRD, optical microscopy). The layer thickness of the obtained materials was in the range of 0.047 -0.5425 mm. The degree of nutrients' release (0.64-0.965 within five hours) were determined with standardized method. Exponential, sigmoidal and power equations were used to describe the kinetics of nutrients' release.

This paper presents the most important issues relating to the infl uence of mineral fertilizers on both the natural environment and human and animal health. The physiological, environmental and economic impact of fertilizer production and application, resulted from a low assimilation of mineral components by crops, has been described. The research on the development and production of a large and diverse group of materials with slow-release properties that can increase the effectiveness of nutrient uptake, alleviate the negative infl uence of fertilizers on the environment and reduce labor and energy consumption associated with the use of conventional fertilizers, has been reviewed.

Controlled release fertilizersThe efficiency of nitrogen assimilation by plants is rather low and this is a serious problem in view of environmental protection. Improvement of nitrogen absorption can be carried out through the developing, producing and applying the controlled release fertilizers. Biodegradable chitosan has been proposed as an alternative material in the production of controlled release fertilizers.