Formulation and characterization of water retention and slow-release urea fertilizer based on Borassus aethiopum starch and Maesopsis eminii hydrogels

Abstract

Environmentally friendly slow-release fertilizers (SRF) based on Borassus aethiopum starch (BAS-SRF) and Maesopsis eminii (ME-SRF) hydrogels were formulated by encapsulating urea into biomaterials using borax as a binder. The SRFs were characterized by FT-IR, SEM and XRD techniques. The gel ratios of the hydrogels were found to be 71.27 ± 0.31 and 57.43 ± 2.27 for BAS-SRF and ME-SRF respectively. Swelling and water retention capacity of the SRFs in distilled water, NaCl, CaCl2, and FeCl3 solutions were evaluated. The water retention ratio at 4 days was similar 14.76% for both BAS-SRF and ME-SRF in soil and 4.67% for soil without the SRFs. The swelling ratio of the SRFs in solution, followed the order Water > NaCl > CaCl2>FeCl3. The swelling kinetics fitted with Scott's second order swelling kinetic model. The fertilizer release of the standard urea (un-capsulated) in distilled water revealed a cumulative release of about 97% within an hour. Whereas the formulated BAS-SRF and ME-SRF (encapsulated) had a cumulative release of 76% and 68% at 24 h and 96 h respectively. Interestingly, a sustained cumulative urea release was observed in soil; about 95% and 92% at 36 days for BAS-SRF and ME-SRF respectively.

Keywords

• Slow-release fertilizer
• Hydrogels
• Urea
• Biomaterial
• Water retention
• Swelling kinetics