PUB - Publikationen an der Universität Bielefeld

Human societies are facing rapid population growth, yet many people in the world are still food insecure. Fertilizers are widely used in agriculture in order to increase land production. However, improper fertilizers have negative effects on the soil as well as on the crops. The rapid release of nutrients from fertilizers not only prevents crops from properly absorbing them, but also destroys the quality of the soil, while unabsorbed nutrients damage our environment through the hydrological cycle. Slow-release fertilizers have become the answer to this problem. This thesis focuses on the formulation of degradable polymeric matrixes as carriers for slow release fertilizers. For this purpose, hydrogels were synthesized by Schiff base reaction based on different cellulose substrates for investigating the release kinetics of different ions from them. The optimized Peleg model was used here to fit the concentration of ions released at different time points to derive the law of release kinetics of ions from cellulose based hydrogels. The SAXS technique was used to analyze the network structure and correlation lengths of the hydrogels. It was shown that different side chains of cellulose affect the correlation length of the hydrogels, leading to changes in the release kinetics. At the same time, the ions themselves also have an effect on the release kinetics, with the valance of the ions being the main factor. In addition, the variation of pH also changes the network structure in the hydrogel. Thus, the effect of different pH on the release kinetics is also considered as one of the factors controlling release. By analysis of the effects of these factors on the release kinetics, the release rate can be controlled in order to achieve a slow release of them. In parallel, cellulose-based slow-release fertilizers were also applied to the cultivation of blueberry plants and their slow-release properties were analyzed in land trials. The contribution of cellulose to the slow release of nutrients was also verified by the experimental results. Moreover, studies of the degradation of hydrogels also proved that cellulose-based slow-release fertilizers can ensure the stability during the release of nutrients, while achieving the ultimate degradation in the natural environment, thus preventing the deposition of chemical substance in the soil which leads to the destruction of them.