P. Villagra’s research while affiliated with Instituto de Investigaciones Agropecuarias and other places

Crop evapotranspiration (ETc) is essential for irrigation scheduling. The amount of water consumed can be estimated by multiplying the reference evapotranspiration (ET0) by a crop coefficient (Kc); the value of Kc is usually obtained from FAO Paper nr 56. In table grapes (Vitis vinifera L.), Kc are obtained from experiments in vines trained on trellis systems; however in Chile, the most used is the overhead trellis system (parronal). Therefore, the objective was to determine water requirements and Kc values of a table grape orchard cv. Thompson Seedless trained on an overhead trellis system in Calle Larga (32 degrees 52 ' 40" S, 70 degrees 37 ' 45" W, 795 m a.s.l.), Aconcagua Valley, Chile, using the Eddy covariance method. During the 2008/2009 and 2009/2010 seasons, the instruments required for ET0 and ETc measurement were installed on a 4 m tower above the soil (2 m above vine canopy). The ET0 was estimated according to the FAO Penman-Monteith equation and ETc by the Eddy covariance method. The Kc was obtained by ratio between ETc and ET0. The maximum ETc was 7 mm d(-1) and total water consumption was 810 mm. The season maximum Kc value of 1.2 was obtained near harvest during the first season, and 20 d before veraison in the second season. The Kc increased linearly with the percentage of intercepted solar radiation (IRS) by the vine canopy at noon, suggesting that an equation to convert the IRS to Kc is more useful than Kc tabulated according to phenology. The equation obtained in this experiment was Kc = 0.012 IRS - 0.1029, R-2 = 0.85.

During the 2008/09 and 2009/10 seasons, net radiation (Rn), latent heat flux (LE), sensible heat flux (H), soil heat flux (G), and crop evapotranspiration (ETc =LE, where λ is latent heat of vaporization) were measured on a drip-irrigated Thompson Seedless vineyard trained on an overhead trellised system ("parronal español"). The experiment was located in Calle Larga, Aconcagua valley, Chile (32°52'40" S, 70°37'45" O, 795 m s.n.m.). LE and H were measured by an eddy correlation system, and reference evapotranspiration (ETo) was calculated using the FAO-Penman-Monteith method. Results indicated that the closure error (ratio of LE+H to Rn-G) decreased as canopy light interception increased (CLI). With 22% CLI closure error was around 20-30%. Over 74% CLI, closure error was around 10 to 20%. Higher closure error with low CLI can be attributed to errors on measurement of G. At 22% CLI the energy partition relative to Rn were 13, 45 and 13% for LE, H and G, respectively. With higher CLI ( 98%), LE, H and G were 81, 0.1 and 1% of Rn respectively. Derived crop coefficients (Kc = ETa/ETo) under an overhead trellised system are higher than those proposed by FAO 56 for table grapes, from near veraison to end of the season. Kc values from budbreak to harvest period increased linearly as CLI increased (Kc = 0.0137*CLI(%) -0.1492).

During the 2008-2009 season, net radiation (Rn) and soil heat flux (G), sensible heat flux (H) and latent heat flux (LE=Λ ETc where ETc is vine evapotranspiration and Λ is the latent heat of vaporization) were measured on a drip-irrigated 'Thompson Seedless' vineyard trained on an overhead trellised system ("parronal español"). The experiment was located in Calle Larga, Aconcagua valley, Chile (32°52'40" S, 70°37'45" O, 795 m a.s.l.). LE and H were obtained from an eddy covariance system. The reference evapotranspiration (ETo) was calculated using the FAO-Penman-Monteith model. Results indicated that the closure (ratio of LE+H to Rn-G) was 0.91 in November '08 and 0.82 in January '09. At flowering (74% solar interception), the mean ratios of LE, H and G to Rn were 0.53, 0.26 and 0.11, respectively. At veraison (98% solar interception) LE, H and G were 0.81, 0.01 and 0.1 of Rn respectively. Also, an increase of crop coefficient (Kc = ETc/ETo) values from October to mid-November was observed. Afterwards, it was almost stable until mid-January when an increase was again observed. A maximum Kc value of 1.3 was reached at veraison.