New Urea Controlled-Release Fertilizers Based on Bentonite and Carnauba Wax

Abstract

Controlled-release fertilizers are interesting alternatives to current commercial chemical fertilizers, which present a higher nutrient release rate, and can negatively impact the ecosystem. In this work, two urea controlled-release fertilizer types were manufactured from carnauba wax (CW), commercial granulated urea (U), and natural and sodium bentonite (Bent-R and Bent-Na, respectively). In the first type, the mechanochemical method produced fertilizers in bars, from a mixture containing different proportions of U, Bent-R, and Bent-Na. In the second type, the dip-coating method was used to coat urea bars with coatings containing different proportions of the Bent-R, Bent-Na, and CW. The cumulative urea release was evaluated over the 30-day incubation period, through soil columns tests and UV/visible spectroscopy. Overall, both fertilizers developed in this work presented lower cumulative urea release than standard fertilizers. On the other hand, the new fertilizers produced from the dip-coating method, provided cumulative urea release lower than that obtained by the mechanochemical method. In summary, carnauba wax and bentonite (raw and sodium modified) are promising materials for developing new urea controlled-release fertilizers. Furthermore, both carnauba wax and bentonite are non-toxic, biodegradable, relatively inexpensive, and created from materials that are easily purchased in Brazil, indicating that the new fertilizers developed in this work have the potential to be produced on a large scale.