A Joint Investigation of Evapotranspiration Depletion of Treated and Non-Treated Saltcedar at the Elephant Butte Delta, New Mexico

Saltcedar (Tamarix sp.) was introduced to the U.S. as an ornamental plant to control soil erosion. But now the control of saltcedar has become a major concern since studies in the past have shown that evapotranspiration (ET) of saltcedar has been reported to range between 3 ft-5 ft of water per year. To study the reduction of saltcedar ET by herbicide treatment, a large area of dense saltcedar was treated, and an adjacent area was left untreated in order to compare the effects of ET losses after herbicide treatment.

Evapotranspiration of saltcedar was measured using the eddy covariance method. A robust one-propeller eddy covariance (OPEC) system and a three- dimensional sonic eddy covariance (3D-SEC) system were used to measure the ET of saltcedar at both the non-treated and herbicide-treated sites. Latent heat flux was estimated as a residual from energy balance. Sensible and latent heat fluxes at both the sites were compared to each other and also with both systems of measurement (OPEC and 3D-SEC).

Evapotranspiration measurements from both sites indicated that the treated saltcedar stand during a comparison of 83 growing days was less than the non-treated site by about 57%. Total ET of 327 mm was measured at the non-treated site and 142 mm at the treated site. For the 149 days of data comparison, during the non-growing season, the treated site had higher ET than the non-treated site by 37%. Total ET of 161 mm at the non-treated site and 220 mm at the treated site was measured. Evapotranspiration of the non-treated site was estimated during the growing season of 2005 using crop coefficient as a function of cumulative GDD (growing degree days) developed based on ET measurements at Bosque del Apache National Wildlife Refuge. The estimated ET for non-treated saltcedar was 1002 mm when compared to measured ET of 386 mm at the treated site, a difference of 61% for 189 days. This was close to the 57% difference (non-treated ET of 327 mm and treated ET of 142 mm) for 83 days determined by direct measurements during the growing season from April 23 through May 11, 2005.

Soil salinity data were also collected from the treated and non-treated sites. The data were collected from October 9, 2004 through July 21, 2005. Soils at the study site were slightly alkaline. The salinity at the treated site was lower than the non-treated site by an average of 33%.