Biodegradable maleic–itaconic polymer-coated phosphatic fertilizer improved phosphorous recovery in calcareous soil

Background: The poor nutrient recovery of phosphatic (P) fertilizers in calcareous soils is a serious worldwide problem resulting in sub-optimal P use efficiency. This is mainly attributed to P fixation with calcium (Ca) and magnesium (Mg) ions in the soil solution. As a result, most of the applied P (in the form of fertilizer) becomes insoluble or immobilized in soil due to complex edaphic processes, making it unavailable to plants. Polymer-coated fertilizers are relatively new approaches to minimizing P-fixation. However, concerns have been recently raised on the environmental effects of synthetic polymers and microplastic loads in agroecosystems. Aim: Here we developed and investigated the effectiveness of biodegradable polymer-coating on commercial diammonium phosphate (DAP) fertilizer to improve P availability in the soil, hence making P more accessible for plant uptake. Methods: The polymers were coated on DAP fertilizer granules, and two products based on increasing polymer concentration (namely, C-1 and C-2, respectively) were achieved. The coated and uncoated DAP granules were characterized for surface properties to confirm the appropriate coating of polymers using scanning electron microscopy (SEM) and crushing strength by a universal telson machine. The biodegradable polymer-coated C-1 and C-2 fertilizers were tested for P availability compared to commercial DAP using spinach as a test plant. Results: The SEM micrographs indicated a uniform coating of biodegradable polymers on DAP granules. Application of C-1 increased the plant's fresh and dry biomass (+10.71% and +18.09%) over commercial DAP, respectively. The C-1 application increased the N, P, and K uptake by +24.9%, +66.7%, and +11% over commercial DAP. In contrast, C-2 produced less biomass than C-1 due to relatively less nutrient uptake and different concentrations of ingredients in C-2. Conclusion: Together, our results showed that the novel biodegradable polymer approach has demonstrated the potential to improve P recovery and agronomic yield in alkaline soils.