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Rainfall Timing and Ammonia Loss from Urea in a Loblolly Pine Plantation

Dep. of Crop and Soil Sci. and Agricultural and Environmental Services Lab. and School of Forest Resources, Univ. of Georgia, 2400 College Station Rd., Athens, GA 30602

View larger version (28K): [in a new window]   Fig. 1. (a) Cumulative loss of NH3 during the period of 14 Mar. to 12 Apr. 2002 following application of 200 kg ha–1 urea-N to midrotation pines as affected by application of 0, 4, and 11 mm of simulated rain on Day 4 following urea application. (b) Cumulative loss of NH3 during the period of 2 to 31 May 2002 following application of 200 kg ha–1 urea-N to midrotation pines as affected by application of 0 and 40 mm of simulated rain on Day 5 following urea application. (c) Cumulative loss of NH3 during the period of 9 Aug. to 7 Sept. 2002 following application of 200 kg ha–1 urea-N to midrotation pines as affected by application of 24 mm of simulated rain to either a bare soil or a normal forest floor the same day as the urea is applied or on Day 7 to a normal forest floor following urea application (bars are standard errors).

View larger version (30K): [in a new window]   Fig. 2. Cumulative loss of NH3 during the period of 16 Sept. to 14 Nov. 2002 following application of 200 kg ha–1 urea-N to midrotation pines as affected by application of 24 mm of simulated rain on Days 16 or 30 of the study (bars are standard errors).

View larger version (31K): [in a new window]   Fig. 3. Cumulative loss of NH3 during a 31-d laboratory study from 200 kg ha–1 urea N, in which 20 mm of simulated rain was applied to a forest floor (packed into acrylic plastic cylinders) at different times with respect to the urea application. Diurnal cycles of temperature (15 to 25°C) and relative humidity (40 to 95%) mimicked the natural cycle (bars are standard errors).

View larger version (24K): [in a new window]   Fig. 4. Urea-derived N found in O and A horizons at the end of a 31-d laboratory study in which 20 mm of simulated rain was applied to a forest floor (packed into acrylic plastic cylinders) at different times with respect to a urea application of 200 kg ha–1 urea N (bars are standard errors).