1. Relative humidity controls ammonia loss from urea applied to loblolly pine
- Author
-
Cabrera, M.L., Kissel, D.E., Craig, J.R., Qafoku, N.P., Vaio, N., Rema, J.A., and Morris, L.A.
- Subjects
Humidity -- Research ,Soil moisture -- Research ,Soil chemistry -- Research ,Earth sciences - Abstract
In the United States, approximately 600,000 ha of pine trees are fertilized with urea each year, with N[H.sub.3] volatilization losses ranging from < 1% to >50% depending on environmental conditions. Previous work showed that the timing of rainfall after urea application plays a significant role in controlling N[H.sub.3] loss, but the effect of other environmental variables is not well understood. We conducted 10 29-d studies under different environmental conditions during 2 yr to identify important variables controlling N[H.sub.3] loss from urea applied to loblolly pine (Pinus taeda L.) at 200 kg N [ha.sup.-1]. Ammonia loss was measured with dynamic chambers that adjusted the rate of air flow through the system based on wind speed at 1 cm above the soil surface. Regression analysis indicated that a variable related to the initial water content of the forest floor and a variable related to the relative humidity (RH) during the study explained 85 to 94% of the observed variability in N[H.sub.3] loss. Relatively high initial water content followed by consistently high RH led to large N[H.sub.3] losses. In contrast, low initial water contents resulted in slow rates of N[H.sub.3] loss, which increased when elevated RH led to an increase in the water content of the forest floor. These results indicate that RH can play a significant role in N[H.sub.3] loss by accelerating urea dissolution and by increasing or decreasing the water content of the forest floor, which in turn can affect the rate of urea hydrolysis. Abbreviations: CRH, critical relative humidity of urea; RH, relative humidity; RH-days, relative humidity-days. doi:10.2136/ssaj2009.0220
- Published
- 2010