Effect of Temperature and Coating Thickness on the Release of Urea from Resin‐Coated Granules¹

Abstract

Resin coatings are very effective in controlling the availability of N from applied urea in moist soil. In leaching studies, 94% of the noncoated urea was recovered in 1 day, compared to a 49% recovery of the N from coated urea (13.2% resin) in 4 weeks of intermittent leaching.Release rates are controlled by the thickness of the coating and the temperature of the medium. Coatings averaging 13.2% resin markedly decreased release of urea, compared to coatings of 9.0% resin. In the range beween 5 to 35C, increased release of urea accompanied increases in temperature. After 4 weeks of incubation and intermittent leaching totaling 20 inches of water, 25 and 67% of the added N were leached from soil at 5 and 35C, respectively. Increasing the temperature 10C was approximately equivalent to doubling the release time within a 16-week period. Increasing the temperature increases expansion of the capsule and the surface area through which diffusion must take place. This effect is probably supplemental to the effect of temperature on the diffusion phenomena per se. Approximately 99% of the capsules were recovered intact after incubation for 16 weeks at four temperatures between 5 and 35C.

Nitrogen Release from Environmentally Smart Nitrogen Fertilizer as Influenced by Soil Series, Temperature, Moisture, and Incubation Method

“…The authors concluded that only small differences of urea N were leached when temperatures ranged from 15 to 30 • C, but there were large differences in ammonium (NH 4 ) and nitrate (NO 3 ) N recovered. Brown, Luebs, and Pratt (1966) suggested that as temperature increased the rate of urea hydrolysis also increased, which explained the differences in NH 4 + recovery among the range of incubation temperatures. If the diffusion rate of urea out of ESN is increased with increasing temperature and urea hydrolysis increases with temperature, it is logical that the diffusion coefficient across the polymer coating also increased.…”

“…Although slight differences were observed along the N-release curve, the number of days for near total N release was very predictable with the buried-bag method. Other researchers have assessed N release by leaching columns filled with sand or soil containing polymer-coated fertilizer (Brown, Luebs, and Pratt 1966;Wang and Alva 1996) or by analysis of total N remaining as a percentage of total N applied (Allen, Hunt, and Terman 1971). The leachate methods have described the release of N from polymer-coated urea in fractions or forms of N leached from the columns.…”

“…These data suggest that a critical temperature may exist between 15 and 20 • C where N release becomes more rapid. When soil temperatures were ≥20 • C, 65 to 90% of the urea N in ESN was released within 30 d. Brown, Luebs, and Pratt (1966) reported that amounts of cumulative N leached from resin-coated urea incubated in sand at 25 and 35 • C for 4 weeks were 84.1 and 90.9%, respectively. The authors concluded that only small differences of urea N were leached when temperatures ranged from 15 to 30 • C, but there were large differences in ammonium (NH 4 ) and nitrate (NO 3 ) N recovered.…”

Inhibition of urease activity in soils

“…One problem, which has been overlooked in most investigations, is that significant hydrolysis of urea by soil urease can occur during extraction of soils for determination of urea (Keeney and Bremner, ISSf The colorimetric method of Watt and Chrisp (195^) has been used to determine urea in soil extracts (Broadbent et al, 1958;Soulldes and Clark, 1958;Simpson and Melsted, 1963;Brown et al, I966;Waid and Pugh, 1957) but this method does not have the sensitivity needed for studies of urea transformations in soils (it was designed for analysis of solutions containing 50-240 ppm of urea), and Keeney and Bremner (1967) and Wald and Pugh (I967) found that some soil extracts contain substances that Interfere with this method.…”

Factors Affecting Nutrient Availability, Placement, Rate, and Application Timing of Controlled-release Fertilizers for Florida Vegetable Production Using Seepage Irrigation

“…TEMPERATURE. The rate of nutrient release from CRF increases with increasing soil temperature, which shortens the release duration (Ahmed et al, 1963;Basu et al, 2010;Brown et al, 1966;Dai et al, 2008;Kochba et al, 1990). Gandeza et al (1991) showed that after 60 d of incubation in water, a polymer-coated fertilizer (PCF) released %20%, 48%, and 80% of the N at 10, 20, and 30°C, respectively.…”