Synthesis of Slow-release Urea Fertilizer Using Starch-based Polymer Nanocomposite Coating and Investigation of Its Effect on Tomato Growth

A significant part of the nitrogen fertilizers due to the high solubility in water, penetrates into the lower parts of the soil and become unavailable to the plant. To prevent nitrogen losses, various methods have been used, of which coatings is the most widely used methods to reduce the rate of dissolution in water. The objective of the current study was to produce novel slow release fertilizers (SRFs) using starch-based polymer nanocomposites (in terms of environmental compatibility and degradability) and to investigate the comparative efficiency of these samples on the growth and nutritional responses of tomatoes. Firstly, two formulations of urea fertilizer coated with starch-based polymer nanocomposite reinforced with biochar nanoparticles (A) and pristine polymer without nanoparticles (B) were synthesized. Then, the effects of two levels (180 and 420 kg/ha or 60 and 140 mg/kg) synthesized SRF samples (A and B) and un-coated urea granule fertilizer (as a control) on morphological characteristics of tomatoes were investigated. A factorial design based on the completely randomized blocks with three replications was performed at Agricultural Biotechnology Research Institute, Karaj. The results showed that the presence of nanoparticles increases the release time of urea from the coating layer, and it was prolonged with increasing the amount of NCNPs because of favorable interfacial polymer-filler interactions. So that, the nitrogen release rate from sample A, at pH= 2, 6 and 10, was respectively decreased 49.46, 18.52 and 45.13% as compared to sample B. Moreover, application of SRF samples increased nitrogen use efficiency, nitrogen agronomic efficiency and apparent nitrogen recovery. So that, the nitrogen use efficiency in fertilizer treatments A and B with usage of 420 kg/ha was respectively increased 7/85 and 14/68% compared to urea fertilizer.