“Smart” Fertilizer with Temperature- and pH-Responsive Behavior via Surface-Initiated Polymerization for Controlled Release of Nutrients

With the fast development of sustainable modern agriculture, there has been a shift toward the development of controlled/slow release fertilizers (CSRFs) that can overcome current limitations of conventional fertilizers. Ideally, CSRFs would release nutrient matching plants demands, even when environmental conditions fluctuate. However, no current CSRFs meet this ideal, especially as nutrient release is affected by temperature and pH. In this study, a “smart” fertilizer with polymer brushes of poly(N,N-dimethylaminoethyl methacrylate) grafting from polydopamine-coated ammonium zinc phosphate via surface-initiated atom-transfer radical polymerization is reported. The structure and morphology of the fertilizer were measured by transmission electron microscopy (TEM); the composition of the product was determined with Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and inductively coupled plasma (ICP) emission spectrometer. Dual-responsive controlled-release behaviors were characterized in water by spectrophotometry and ICP, and results demonstrate the “smart” fertilizer shows excellent temperature- and pH-responsive behavior to release nutrients according to the ambient environment. The nutrients release rate can be obviously accelerated in an acidic pH (below pKₐ) medium at a definite temperature. In addition, low temperature (below LCST) can accelerate the nutrients release rate in a basic medium (above pKₐ), which is contrasting to the reduction of nutrients release rate at high temperature (above LCST) in the same medium. The pH- and temperature-responsive “smart” fertilizer will improve nutrients availability and avoid excessive release of nutrients causing damage to plant roots at high temperature, which indicating that the stimuli-responsive system has potential application in sustainable modern agriculture.