|Evett, Steven - Steve|
Submitted to: American Society of Agricultural Engineers Meetings Papers
Publication Type: Other
Publication Acceptance Date: 7/12/1998
Publication Date: N/A
Technical Abstract: The Bowen ratio-energy balance (BREB) method is used to estimate latent heat flux to quantify crop water use, evaluate water use models, or investigate aspects of plant-water relations. Few studies have tested the BREB method in an environment where significant sensible heat advection occurs. We compared and contrasted daily and half-hourly BREB estimates of firrigated alfalfa latent heat flux with precision weighing lysimeters measurements in a semi-arid, advective environment. The research was conducted near Bushland, TX, between the third and fourth cutting of alfalfa in 1997 and before the first cutting in 1998. The BREB method used vertically exchanged temperature and humidity sensors to measure gradients. Net radiation and soil heat flux were measured with instruments installed at two 3- x 3- x 2.3-m, monolithic, continuously weighed lysimeters located in the centers of adjacent 4.7 ha fields. Latent heat flux often exceeded the sum of net radiation and soil heat flux, and there was significant sensible heat advection on 14 out of 22 days. Daily ET estimated by the BREB method agreed within 3% of lysimeter ET in 1997, but overestimated ET in 1998, especially when rates were greater than 6 mm d-1. The BREB method also tended to overestimate half-hourly measurements of ET. The BREB method overestimated diurnal latent heat flux during the morning hours regardless of whether there was sensible heat advection, agreed within 10% during mid-day, and either overestimated (in 1998) or underestimated (in 1997) latent heat flux during the afternoon when sensible heat advection was most likely to occur.