Biodegradable fertilizer nanocomposite hydrogel based on poly(vinyl alcohol)/kaolin/diammonium hydrogen phosphate (DAhP) for controlled release of phosphate

Ever-degrading environment due to the application of a large amount of agrochemicals, like fertilizers into the soil, has raised the concern for implementing such measures which would not only reduce the chemical incorporation into the soil, but will also benefit the crops by shooting up the fertilizer utilization by the same. Henceforth, biodegradable formulations for phosphate are essentially required to undergird the evolution of modern day agriculture. Naturally occurring phosphate could not suffice the demands of global agriculture, and so, it has to be applied synthetically in the form of agrochemical. Taking the very facts into consideration, the preparation of a novel biodegradable formulation of nanocomposite hydrogel using PVA as polymeric matrix, kaolin clay as mechanical binder and DAhP as phosphate fertilizer is attempted in the present study. The analysis of final formulation was done using techniques like FT-IR, XRD and SEM. The synthesized compound is named PDK. It shows 66.6 g/g equilibrium swelling; shows 10 times swelling its own weight in 1 h of immersion and attained equilibrium after 3 h. Factors affecting swelling behavior like content of kaolin, temperature and pH have also been investigated which revealed that 1–3 wt% kaolin, 35–40 °C temperature and 6–7 pH are the best optimum conditions for PDK hydrogel to show best results in release and swelling. The release study for phosphate was done by volumetric ammonium phosphomolybdate method by dispersing the sample in water and soil and checking the release at an interval of 3 days for 30 days which revealed 88.8% release in water and 76.3% release in soil. The formulation shows considerable controlled release of DAhP and also presents a scope for the development of biodegradable phosphate-based controlled release fertilizer.