Potential of Zeolite-Based Urea Formulations as Slow-Release Nitrogen Fertilizer

Rapid release of nitrogen (N) from urea fertilizer results in heavy N losses (40-70%) and low nutrient use efficiency. Structural channels and sorption of cations make zeolites attractive for NH4+ adsorption and delayed release. Zeolite-based slow-release fertilizers can be prepared by impregnating zeolite with molten urea. Locally mined natural zeolite was characterized and then zeolite impregnated urea formulations were incubated with soil. The treatments were i) No fertilizer, ii) Sole urea, iii) Zeolitic urea 1:3, iv) Zeolitic urea 1:2, v) Zeolitic urea 1:1, vi) Zeolitic urea 2:1, and vii) Zeolitic urea 3:1 applied at two moisture conditions (flooded and non-flooded). Sampling was carried out at regular intervals and analyzed for release of NH4-N, NO3N and NH3 volatilization. Results of X-Ray diffraction spectra and microscopic analysis confirmed the zeolite structure. The zeolitic urea 1:1 and formulations with higher zeolite ratios (zeolitic urea 2:1 and 3:1) delayed the release of NH4-N up to day 14. Whereas, sole urea and zeolitic urea 1:3 and 1:2 quickly released NH4-N by attaining peak at day 7 of incubation. Flooded condition released NH4-N earlier than non-flooded condition. Release of NO3-N was also delayed by zeolitic urea formulations as compared with urea alone by attaining peaks between 28 and 42 days of incubation and maintaining the highest nitrates with zeolitic urea 1:1 till the end of experiment. Ammonia volatilization was as high as 44% of applied N with urea alone while minimum loss of applied N i.e., 29% was recorded with zeolitic urea 1:1. Flooded conditions showed ammonia volatilization 2 to 3 days earlier than non-flooded condition. Results suggested that zeolitic urea 1:1 can be successfully used as slow-release N fertilizer both under flooded and non-flooded soil conditions.