Slow delivery of a nitrification inhibitor (dicyandiamide) to soil using a biodegradable hydrogel of chitosan

Abstract

h i g h l i g h t sDicyandiamide (DCD) was encapsulated in glyoxal-crosslinked chitosan hydrogel beads. Chitosan delayed the release of nitrification inhibitor DCD in water and soil. DCD release was controlled by glyoxal polymerisation inside chitosan. The higher glyoxal polymerisation the more delayed DCD release in water or in soil. The higher glyoxal polymerisation the less DCD encapsulated in the beads. a r t i c l e i n f o b s t r a c tUsing chemical inhibitors to reduce soil nitrification decreases emissions of environmental damaging nitrate and nitrous oxide and improves nitrogen use efficiency in agricultural systems. The efficacy of nitrification inhibitors such as dicyandiamide (DCD) is limited in soil due to biodegradation. This study investigated if the persistence of DCD could be sustained in soil by slow release from a chitosan hydrogel. DCD was encapsulated in glyoxal-crosslinked chitosan beads where excess glyoxal was (i) partly removed (C beads) or (ii) allowed to dry (CG beads). The beads were tested in water and in soil. The beads contained two fractions of DCD: one which was quickly released in water, and one which was not. A large DCD fraction within C beads was readily available: 84% of total DCD bead content was released after 9 h immersion in water, while between 74% and 98% was released after 7 d in soil under low to high moisture conditions. A lower percentage of encapsulated DCD was readily released from CG beads: 19% after 9 h in water, and 33% after 7 d in soil under high rainfall conditions. Kinetic analysis indicated that the release in water occurred by quasi-Fickian diffusion. The results also suggest that DCD release was controlled by bead erosion and the leaching of glyoxal derivatives, predominantly a glyoxal-DCD adduct whose release was positively correlated with that of DCD (R 2 = 0.99, p 6 0.0001). Therefore, novel chitosan/glyoxal composite beads show a promising slow-release potential in soil for agrochemicals like DCD.

Recent Advances in Designing Hydrogels from Chitin and Chitin-Derivatives and their Impact on Environment and Agriculture: A Review

“…The DCD encapsulated on hydrogel, made of Cs crosslinked by glyoxal, released the DCD slowly: 19% under 9 h as immersed in water; and only 33% after 7 days in soil even under high rainfall conditions. 130 Higher content of glyoxal leads to a more crosslinked matrix promoting a delay in the release of DCD in water and in soil, as well.…”

“…129, 130 Wu and Liu (2008) performed aspersion of hydrogel to encapsulate NPK fertilizer granules using a rotating reactor. 131 Spherical nanoparticles of Cs and polymethacrylic acid were prepared by Corradini et al 132 aiming the loading and further release of NPK fertilizers as potential use in agriculture.…”

Plant acquisition and metabolism of the synthetic nitrification inhibitor dicyandiamide and naturally-occurring guanidine from agricultural soils

“…A range of application routes for DCD have been investigated including introduction to urine patches by oral administration to cattle (O'Connor et al 2013;Welten et al 2013), infusion of DCD into the rumen or abomasum of sheep (Ledgard et al 2008), incorporation into fertiliser granules or addition of DCD in a biodegradable hydrogel to slow its release in soil (Minet et al 2013). However, the simplest, least controversial and consequently most widespread route is direct application to soil.…”

The effect of the nitrification inhibitor dicyandiamide (DCD) on spring and annual herbage production in urine patches when applied in late summer or early autumn

“…The risk of DCD degradation by high temperature must be reduced by perhaps developing a technology to allow for the slow release of DCD into the soil over a period of time. This is currently being investigated in Ireland (Minet et al ., ) but the technology requires considerably more development.…”