📖 ABSTRACT/OVERVIEW
Nitrogen use efficiency in Nigerian smallholder agriculture rarely exceeds thirty percent due to volatilisation, leaching, and denitrification losses from conventional granular urea applied without precision, creating both food insecurity and nitrogen pollution externalities that nano-enabled controlled-release fertiliser technology can potentially address using Nigerian mineral resources as coating matrices. This study develops an original nano-enabled slow-release fertiliser system by coating urea granules with nanocomposite materials derived from Nigerian halloysite nanoclay from Ogun State and hydroxyapatite nanorods synthesised from Nigerian phosphate rock, functionalised with a biopolymer crosslinked network of hydroxypropyl methylcellulose and chitosan. Halloysite and hydroxyapatite are characterised by X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller analysis, and surface chemistry by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Coating formulation is optimised for film thickness, coating uniformity, and mechanical integrity using a fluidised bed coating system. Nitrogen release kinetics from coated urea granules are measured in water and soil at temperatures from 25 to 45 degrees Celsius and soil moisture levels from wilting point to field capacity, fitted to the Korsmeyer-Peppas power law model to identify Fickian and anomalous release mechanisms. Greenhouse and field evaluation experiments are conducted across three sites in Kano, Sokoto, and Jigawa States using pearl millet and sorghum as test crops, measuring agronomic nitrogen use efficiency, crop nitrogen uptake, grain yield, and soil mineral nitrogen dynamics. An original membrane permeability model governing nitrogen diffusion through the nanocomposite coating under semi-arid soil temperature and moisture regimes is developed. Life cycle assessment and techno-economic analysis evaluate the environmental and commercial viability. Keywords: slow-release fertiliser, halloysite nanoclay, nitrogen use efficiency, semi-arid agriculture, nanocomposite coating
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