vapotranspiration over a camelina crop at Maricopa, rizona

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 ofwater depletion: 40, 55, 65, and 75%. Six supplemental plots evaluatedwater stress with 85% soil water depletion. A surface energy balancemodel, utilizingmeteorological and radiometric observations within the plots, was implemented to estimate latent heat fluxes from the camelina canopy at 15-min intervals duringmost 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 observationsof soilwater depletion, obtained fromsoil neutronprobeprofiles. 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 0.8mmd−1, R2 > 0.78, and bias <0.76mmd−1. Average yield for the camelina crop was 1000± 310kgha−1. Average total oil content was 41.4 ± 3.8% byweight. Oil content was predicted by yield with fair accuracy where R2 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 secondarywater 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 333–423mm. The ET results showed that the surface energy balance is a feasible and valuable technique formonitoring 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. requirements. Camelina seeds have about 40% oil content . Introduction amelina sativa (L.) Crantz is an oil seed crop with thousands f years of cultivation (Schultze-Motel, 1979; Henriksen and obinson, 1996) that is undergoing resurgent interest due to Mention of trade names or proprietary products in this article does n nd does not imply its approval to the exclusion of other products that ∗ Corresponding author. Tel.: +1 520 316 6371; fax: +1 520 316 6330. E-mail address: [email protected] (A.N. French). 926-6690/$ – see front matter. Published by Elsevier B.V. oi:10.1016/j.indcrop.2008.06.001 Published by Elsevier B.V. its attractive oil characteristics and relatively low agronomic ot constitute a guarantee or warranty of the product by the USDA may also be suitable. and are high in unsaturated oils such as Omega 3 fatty acids (Putnam et al., 1993; Budin et al., 1995; Bonjean and Goffic, 1999; Zubr, 2003), offering a variety of culinary and rod 290 industr ial crops and p industrial applications (Putnam et al., 1993; Shukla et al., 2002; Fröhlich and Rice, 2005; Vollmann et al., 2007). Camelina has a short growing season (∼80days to maturity), has lower nitrogen requirements than the competitor crops canola and sunflower (Putnam et al., 1993), and can be used in mixed cropping systems for weed management (Saucke and Ackermann, 2006; Paulsen, 2007). Geographic effects upon yield have been reported by (Zubr, 2003; Gugel and Falk, 2006). Budin et al. (1995), Angelini et al. (1997), and Vollmann et al. (2007) discuss camelina oil yield and content. Camelina also appears to be heat and drought tolerant (Putnam et al., 1993; Angelini et al., 1997), characteristics that have strong appeal for growers in arid lands. For the southwestern U.S.A. in particular, camelina may be a valuable alternative crop towheat or cotton in the face of long-standing drought, urbanization and strong competition for tight water supplies. However, camelina has been commonly grown in rain fed environments, and guidance for irrigation schedules is sparse. In the face of this lack of knowledge, arid-land growers would likely have to rely upon irrigation experience gained from related oilseed crops such as rapeseed or lesquerella (Hunsaker et al., 1998). Clearly, in order for camelina to become economically viable in irrigated semi-arid environments that reliance needs to be replaced with knowledge specific to camelina. One way to gain that knowledge is to grow camelina in experimental plots with variable irrigation levels and then to observe and estimate resulting evapotranspiration (ET) and yield values. Estimates for ET can be made from frequent observations of soil water throughout the growing season (Evett and Steiner, 1995; Hunsaker et al., 1998, 2005) and can establish irrigation needs for a specific location and soil type. By accounting for water depletions in the soil root zone, water losses from deep percolation, and water gains from irrigation and rainfall, ET over the crop can be estimated to better than 1mm over daily to weekly time intervals. With some loss of accuracy, it is also possible to estimate ET by using crop coefficient/ET models such as FAO-56 (Allen et al., 1998) or by monitoring temporal changes in vegetation canopy densities (Hunsaker et al., 2007). An alternative ET estimation approach that is generally applicable and has the potential to further reduce demanding field acquisition procedures is to estimate the surface energy balance using the equation: