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Dew deposition is often overlooked in humid regions, such as the southeastern USA, but may play an important role in nutrient cycling for surface-applied fertilizers and broiler litter. The objectives of this study were to measure dew in a pasture and to evaluate the effect of simulated dew on NH3 volatilization in a laboratory study. A microlysimeter method was used to measure dew in a tall fescue (Festuca arundinacea Schreb.) and bermudagrass (Cynodon dactylon L.) pasture over 206 d. In the 206 d measured, 119 d received dew with an average dew fall of 0.19 mm and greater events observed in the cooler spring and fall months. dew accumulated during the measurement period accounted for 6% of the precipitation measured. Under lab conditions, the effect of simulated, daily dew (0.2 mm) on NH3 volatilization from surface-applied broiler litter to air-dry soil was evaluated under diurnal fluctuations of temperature (6-27°C) and relative humidity (26-91%) for 15 d. dew application significantly increased NH3 volatilization losses (31% of the applied NH4-N and 5% of the applied total nitrogen [TN]) when compared with NH3 losses in the absence of dew (15% of the applied NH4-N and 2.4% of the applied TN). These results suggest that dew may affect NH3 losses from surface-applied broiler litter under dry field conditions. [ABSTRACT FROM AUTHOR]

Broiler litter is commonly surface applied to grasslands as fertilizer in the southeastern United States. Surface application may lead to losses of P in surface runoff and to losses of N through NH3 volatilization. Adding gypsum to broiler litter can reduce water-soluble P and, therefore, the potential for surface water contamination, but no information is currently available on the effect of gypsum on NH3 volatilization when broiler litter is applied to soil. We conducted three laboratory studies to evaluate the effect of adding flue-gas desulfurization (FGD) gypsum to broiler litter or soil on NH3 volatilized and N mineralized. In two studies, soil with or without 0.01 g FGD gypsum g-1 soil was packed into acrylic columns and broiler litter with or without 0.25 g FGD gypsum g-1 litter was applied on the soil surface and incubated at 25°C for 15 d. In a third study, litter with or without 0.25 g FGD gypsum g-1 litter was mixed with soil and incubated at 25°C for 63 d. Our results showed that the addition of FGD gypsum to broiler litter or soil did not affect net N mineralized or NH3 volatilized when litter was surface applied. Similarly, the addition of FGD gypsum to broiler litter did not affect net N mineralized when broiler litter was incorporated into soil. Thus, the addition of FGD gypsum at these rates does not change NH3 loss or N mineralized from broiler litter. [ABSTRACT FROM AUTHOR]