Plant stimuli-responsive biodegradable polymers for the use in timed release fertilizer coatings

The use of nitrogen-based fertilizers continues to accelerate with human population growth and increases in global food requirements. Enhanced efficiency fertilizers (EEFs) have been developed to improve the synchronization between nutrient supply and crop nutrient demand. However, many of the current controlled release fertilizers are coated with non-degradable polymers that contribute to accumulation of microplastics within ecosystems. This thesis describes research towards the development of a new class of fertilizer coatings using a self-immolative polymer known as poly (ethyl glyoxylate) (PEtG). PEtG itself does not have suitable properties to produce a viable coating but once blended with another degradable polyester such as polycaprolactone its overall properties improve. I demonstrated that PEtG with a pH-sensitive carbamate end-cap degraded in response to the presence of plant roots, which suggests that fertilizer coatings could be developed with PEtG that may release nutrients more efficiently while degrading into innocuous by products

Application of biochar for the treatment of retting effluent and use as growth substrate

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Nitrogen transfer from cover crops to the subsequent grain crop and the influence of variability in winter conditions

Cover crops, which are used to provide ground cover after the harvest of the grain crop, can potentially improve the sustainability of agroecosystems by reducing nutrient losses. However, few data are available to document the extent to which cover crops improve both the retention of soil nitrogen (N) and the transfer of this N to the grain crop. The efficiency of this N transfer may be further influenced by variation in winter soil temperature; for example, reduced snow cover can increase the frequency and intensity of soil freezing, which can affect the survival of cover crops and the timing of the decomposition of their residues. I quantified N transfer from cover crops (legumes, non-legumes and mixtures) to the subsequent corn crop using 15N tracer. Residue swapping was used to isolate the individual contributions of the aboveground and belowground N components of the cover crops. N transfer responses to soil temperature variability over the winter were examined via snow removal and pulsed warming from overhead heaters. My results revealed that the belowground N pool contributed substantially more to N retention and N transfer than the aboveground N pool. However, less than 10% of the 15N added to the soil was transferred to the corn, while the majority remained in the soil. In addition, increased soil freezing reduced the effectiveness of the cover crops in transferring N to the corn, with legumes being more susceptible to N losses than non-legumes. Year-to-year variability in cover crop establishment and productivity also had strong effects on the effectiveness of the cover crops in retaining and transferring N. Overall, my results reveal that while the scavenging of N by cover crops after harvest of the main crop may not provide a substantial contribution of N to the grain crop the following year, this scavenging may be important for reducing N losses to the surrounding environment

Development of Fertilizer Coatings from Polyglyoxylate-Polyester Blends Responsive to Root-Driven pH Change

Copyright © 2019 American Chemical Society. Many current controlled-release fertilizers (CRFs) are coated with nonbiodegradable polymers that can contribute to microplastic pollution. Here, coatings of self-immolative poly(ethyl glyoxylate) (PEtG) capped with a carbamate and blended with polycaprolactone (PCL) or poly(l-lactic acid) (PLA) were evaluated. They were designed to depolymerize and release fertilizers in the vicinity of plant roots, where the pH is lower than that in the surrounding environment. PEtG/PCL coatings exhibited significant temperature and pH effects, requiring 18 days at pH 5 and 30 °C, compared to 77 days at pH 7 and 22 °C, to reach 15% mass loss. Plant roots were also effective in triggering coating degradation. Spray-coating and melt-coating were explored, with the latter being more effective in providing pellets that retained urea prior to polymer degradation. Finally, PEtG/PCL-coated pellets promoted plant growth to a similar degree or better than currently available CRFs

Photoinduced Degradation of Polymer Films Using Polyglyoxylate-Polyester Blends and Copolymers

© 2018 American Chemical Society. Polymeric coatings are commonly employed to alter surface properties. While some coatings are designed to remain stable over a prolonged period, in applications such as pharmaceuticals or fertilizers, the coating is designed to erode and reveal or release the underlying material. Self-immolative polymers (SIPs) undergo depolymerization following the cleavage of stimuli-responsive end-caps from their termini, enabling controlled depolymerization in the solid state and in solution. Poly(ethyl glyoxylate) (PEtG) is a promising SIP because of its depolymerization to benign products, but its amorphous structure and low glass-transition temperature make it unsuitable alone for coating applications. This study explored the blending of PEtG with polyesters including polycaprolactone (PCL), poly(l-lactic acid), and poly(R-3-hydroxybutyrate). Block copolymers of PEtG with PCL were also synthesized and studied. It was found that the phase separation behavior and consequently the thermal and mechanical properties of the materials could be tuned according to the composition of the blend, while the stimuli-responsive degradation of PEtG was retained in the blends. This work therefore provides a framework for the application of PEtG-based coatings in applications ranging from pharmaceuticals to agricultural products