Development of urea adsorbed activated carbon-bentonite composite as a green controlled-release fertilizer and its effect on growth productivity of purslane, Portulaca oleracea L. / Pravin Vejan

Pravin , Vejan (2024) Development of urea adsorbed activated carbon-bentonite composite as a green controlled-release fertilizer and its effect on growth productivity of purslane, Portulaca oleracea L. / Pravin Vejan. PhD thesis, Universiti Malaya.

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Abstract

Urea fertilizer is widely used to increase crop production yield. However, low use efficiency of urea fertilizer could lead to its excessive usage, cause groundwater contamination, eutrophication, and the increased emission of global greenhouse gases. Controlled-release urea fertilizers (CRUF) can effectively reduce the amount of urea fertilizer used, and improve the availability of urea fertilizer, which is conducive to the plant growth, and at the same time overcome the environmental issues associated with urea fertilizers. Therefore, it is imperative to develop CRUF as an alternative to conventional urea fertilizer. Basically, CRUF consist of internal urea fertilizer and outer coating materials of polymers which delays the release of urea. However, most of the polymers used are not only increase the cost of CRUF, but also non-biodegradability, toxicity, and often causes pollution and ecological damage to the soul. With the increasing awareness of environmental protection, more and more attention has been paid to the usage of biodegradable materials such as natural polymers and porous inorganic materials such as biochar, activated carbon, bentonite, perlite, zeolite and so on. As the first objective of this study, the urea adsorption capacity of oil palm kernel shell biochar (OPKS-B) and oil palm kernel shell activated carbon (OPKS-AC) was evaluated. The second objective of this study was then designed to evaluate the physicochemical characteristics of CRUF produced using thermal infusion of urea fertilizer into activated carbon in existing of bentonite. The third objective was achieved with the investigation of the controlled-release properties of CRUF and its impact on growth performance of Portulaca oleracea L. The OPKS-AC with high surface area and well-developed porous structure is used in this study. Bentonite, a naturally available mineral silicate, would be ideal for CRUF production due to its swelling capacity and good water retention properties. In this study, urea was thermally infused into the OPKS-activated carbon-bentonite composite biomaterial to produce a novel activated carbon composite-based urea fertilizer (CRUF) as potential green controlled release urea fertilizer. The CRUF was subjected to characterization studies such as ultimate analysis, thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (FESEM-EDX) and nitrogen release in water and soil studies. The CRUF has molten urea evenly infused on the pores of the composite with superior characterization properties and nitrogen release study compared to urea, urea/OPKS-AC thermally infused and commercial CRUF. The CRUF has been applied in glasshouse studies with a test crop, purslane (Portulaca oleracea L.), as an environmentally friendly fertilizer. The CRUF synthesized showed significant effectiveness regarding soil properties, plant nutrient uptake, non-enzymatic antioxidants, and growth parameters of purslane. CRUF significantly improved the (p<0.5) height (12.80cm), biomass (31.38g) and total plant nitrogen (6.67%) of purslane while indicating decreasing trends for non-enzymatic antioxidants. Therefore, CRUF as a green fertilizer showed promising attributes for the uplifting of current unsustainable agricultural practices to a more economically and environmentally safer.

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