Nitrogen Release from Slow-Release Fertilizers as Affected by Soil Type and Temperature

Loss of N from fertilized agricultural soils is a serious problem that can negatively affect environmental quality. Nitrogen loss can be moderated by using slow-release fertilizer (SRF) products (e.g., those created through condensation of urea and formaldehyde) in place of 100% water-soluble N. Release of N from SRFs is affected by the soil environment. To evaluate soil effects on N release, we conducted an incubation study in which temperature and soil type were varied. Four SRFs were studied: liquid Nitamin 30L (L30), liquid Nitamin RUAG 521G30 (G30), granular Nitamin 42G (N42) (all from Georgia Pacific Chemicals, Decatur, GA), and granular Nitroform (NF) (Agrium Advanced Technologies, Loveland, CO). The fertilizers were incubated for 78 d at 20, 25, and 30 degrees C in a sandy soil and at 25 degrees C in a loamy soil. Differential N release kinetics of the N sources were determined by measuring NH4-N and NO3-N concentrations throughout the incubation. Net N released as a percentage of total N in the fertilizer was significantly affected by N source, temperature, time, and soil type. Increasing temperature increased net N release. The N release rate decreased in the order N42 > G30 > L30 > NF in the sandy soil and G30 > N42 > L30 > NF in the loamy soil. Overall, the release rates of these fertilizers were greater in the loamy soil. The N release characteristics determined in this study can help in the selection of the appropriate SRF source for crops grown under different soil and climatic conditions to improve N use efficiency and minimize N loss to the environment.