Bobby Golden1, Nathan Slaton2, Colin G. Massey1, Elliot T. Maschmann1, and Richard J. Norman1. (1) Crop, Soil, and Environmental Sciences, University of Arkansas, 1366 W. Altheimer Dr., Fayetteville, AR 72704, (2) Crop, Soil, and Environmental Sciences Department, University of Arkansas, 115 Plant Science Building, Fayetteville, AR 72701
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.