Synthesis of Poly(vinyl alcohol) and Liquid Paraffin-Based Controlled Release Nitrogen-Phosphorus Formulations for Improving Phosphorus Use Efficiency in Wheat

Polymer coating of water soluble fertilizers to curb excess solubilization of nutrients is well-acknowledged fact. Lack of information on phosphorus (P) release from controlled release nitrogen-phosphorus (NP) formulation and its impact on nutrient use indices has driven us to conduct this experiment. We developed NP formulations by reacting liquid ammonia and orthophosphoric acid in laboratory. Resulting NP formulations were characterized by solubility fractions, microscopy, spectroscopy, and X-ray diffraction. After coating with poly(vinyl alcohol) (PVA) and liquid paraffin (LP) at 2 and 3 w/w% concentration, P release kinetics and temperature sensitivity (Q10) of the formulations were compared with diammonium phosphate (DAP) at 20 and 30 °C temperature in a P-deficient soil for 120 h of incubation. Finally, nutrient use efficiency and relative efficiency indices were determined from a greenhouse experiment in potted soil to assess the effect of polymer-coated formulations and of DAP at two application rates in comparison with a non-P amended control. Laboratory synthesized NP formulations were alkaline in reaction, definite cubical to hexagonal crystalline structure with smooth surface generating peaks related to P and N in fingerprinting region of Fourier transform infrared spectroscopy. Polymer coating of NP formulations delayed the P release compared with DAP, while LP-coated formulations showing slower P release than PVA-based coatings. Despite LP-coated formulations showed greater temperature sensitivity (Q10), the PVA-based formulation significantly increased yield and biomass accumulation of wheat, with concomitant increase in crop P uptake and P use efficiency. Both LP and PVA-coated formulations showed a significant residual P accumulation in post-harvest soils. The findings underline the potential of polymer coating technology for enhancing P use efficiencies, thereby reducing environmental P footprints.