Evapotranspiration over a camelina crop at Maricopa, Arizona

Evapotranspiration (ET) over an oilseed crop, Camelina sativa, was evaluated for an experimental plot in,Maricopa, Arizona between December 2006 and April 2007. Camelina (cv. Robinson) was grown in a 1.3-ha field in a randomized design containing 32 plots replicated for four levels of water depletion: 40, 55, 65, and 75%. Six supplemental plots evaluated water stress with 85% soil water depletion. A surface energy balance model, utilizing meteorological and radiometric observations within the plots, was implemented to estimate latent heat fluxes from the camelina. canopy at 15-min intervals during most of the growing season. The latent heat fluxes were then summed to produce daily estimates of ET. A distinct aspect of the model was the incorporation of canopy thermal infrared observations at 15 different locations, which allow plant water stress detection. The resulting ET values were compared with independent observations of soil water depletion, obtained from soil neutron probe profiles. Agreement on a plot-by-plot basis between modeled and observed ET values was very good, where root mean squared errors (RMSE) were usually less than 0.8 mm d(-1), R-2 > 0.78, and bias <0.76 mm d(-1). Average yield for the camelina crop was 1000 +/- 310 kg ha(-1). Average total oil content was 41.4 +/- 3.8% by weight. Oil content was predicted by yield with fair accuracy where R-2 was 0.425 and RMSE was 2.36%. Correlation between resultant camelina yield and total ET was weak; the four main water depletion treatment plots showed no dependence of yield upon cumulative ET. The secondary water stress treatment plots, however, did show dependence, where a 20% reduction in cumulative ET resulted in a corresponding 24% reduction in yield. Hence seasonal camelina water minimally required 333-423 mm. The ET results showed that the surface energy balance is a feasible and valuable technique for monitoring crop water requirement over this potential oil seed crop. Further work is needed to characterize the relation between camelina. yield and ET, including tests of different varieties and levels of fertilization. Published by Elsevier B.V.