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

Nitrogen release from polymer-coated urea must be in synchrony with the period of rapid plant development where N is consumed in large amounts.  The objective was to characterize the N-release rate of Environmentally Smart N (ESN) as affected by soil series, temperature, soil moisture, and incubation method. Laboratory incubations to characterize ESN-N release evaluated temperature (Calhoun series at 15, 20, 25, and 30°C), soil moisture (Calhoun series at 125, 188, 250, and 380 g H₂O kg^-1), soil (Beulah, Dewitt, Hillemann, Perry, and Sharkey series), and incubation method (Henry series, rumen bag vs no bag) for 40 d. A rumen bag containing 38-44 mg ESN-N was buried in 400 g soil and incubated at 25°C and 250 g H₂O kg^-1 soil except in experiments where temperature, moisture, or method were varied.  The amount of N remaining in ESN was determined every 5 d by combustion. Within each experiment the amount of N remaining as affected by time was determined using regression analysis. Nitrogen release from ESN varied slightly among soils, and proceeded more rapidly in clayey soils between 5 and 35 d, but by 40 d the amount of N remaining was similar among all soils. Soil moisture had minimal influence on the N remaining in ESN. Soil temperature had the greatest effect on ESN-N content across time with N release occurring more rapidly as temperature increased.  The rate of ESN-N release proceeded slightly faster when ESN was distributed throughout the soil (no bag) rather than in a rumen bag, but the time for near complete release was similar between methods. Overall, when soil temperatures are ³20ºC, N release from ESN was >85% complete by 40 d, regardless of soil series and moisture. The rumen bag is an efficient method for characterizing the time needed for near complete release of ESN-N.