Controlled release fertilizer encapsulated by a κ-carrageenan hydrogel

Rozo, Gladys; Bohorques, Laura; Santamaría, Johanna

doi:10.1590/0104-1428.02719

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ORIGINAL ARTICLE • Polímeros 29 (3) • 2019 • https://doi.org/10.1590/0104-1428.02719 copy

Controlled release fertilizer encapsulated by a κ-carrageenan hydrogel

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

The release kinetics of nitrogen and phosphorous of a granulated fertilizer, encapsulated in a κ-carrageenan-based hydrogel (CBH), was evaluated in order to determine its release mechanism given the potential this hydrogel has as coating material for controlled release fertilizers (CFRs). The effect of pH on the release properties was also investigated. The relationship between the NH₄⁺, NO₃^-, and PO₄^3- release of encapsulated fertilizers and time was determined by short- and long-term laboratory incubations. The mechanism of the release of nutrient ions was determined by comparing the release data with the zero-order, first-order, Higuchi, Hixon-Crowell and Korsmeyer-Peppas kinetic models. The findings showed that the Korsmeyer-Peppas model could be used to describe the release characteristics of the nutrients in the encapsulated fertilizers and that non-Fickian diffusion is the main release mechanism. The experimental hydrogel showed a high water retention capacity able to absorb 300 times its weight water.

Keywords:
carrageenan; controlled release fertilizers; hydropolymers; release behavior

Nutrient	pH	Kinetic Models
		Zero Order		First Order		Higuchi		Hixson		Korsmeyer-Peppas
		$Q_{t} = Q_{o} + K_{o} t$		$l n Q = l n Q_{o} + K_{1} t$		$Q_{t} = K_{H} \sqrt t$		$Q_{o}^{1 / 3} - Q_{t}^{1 / 3} = K_{s} t$		$Q_{t} / Q_{\infty} = K_{k} t^{n}$
		K	R²	K	R²	K	R²	K	R²	n	K	R²
NO₃^-	4.5	8.99	0.95	0.93	0.53	5.09	0.97	0.19	0.55	0.61	0.35	0.99
	5.5	7.70	0.71	0.84	0.44	3.32	0.91	0.12	0.74	0.44	0.65	0.95
	6.3	18.11	0.58	1.02	0.84	9.55	0.77	0.32	0.63	0.54	0.38	0.92
NH₄⁺	4.5	5.95	0.92	0.75	0.61	6.00	0.96	0.15	0.49	0.64	0.11	0.98
	5.5	4.93	0.95	0.70	0.73	2.51	0.95	0.07	0.94	0.55	0.33	0.99
	6.3	11.21	0.82	0.84	0.52	1.07	0.96	0.18	0.87	0.62	0.21	0.98
PO₄^-3	4.5	2.00	0.92	0.71	0.77	11.18	0.86	0.01	0.94	0.56	0.31	0.82
PO₄^-3	5.5	6.38	0.73	0.26	0.38	0.97	0.94	0.10	0.78	0.67	0.40	0.97

Release exponent (n)	Nutrient transport mechanism	Rates as a function of time
0.45	Fickian diffusion	t-^0.5
>0.45 -0.89	Non Fickian transport	t^n-1
0.89	Case II transport	Zero order release
>0.89	Super case II transport	t^n-1

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[1] * gladys.rozo@utadeo.edu.co