Some Results of Evapotranspiration Measured by Three Weighing Lysimeters in La Mancha, Spain

In semiarid environments with a shortage of water resources and a risk of overexplotation, it is essential to improve the accuracy of the estimation of crop water requirements to reduce water use and increase water productivity. For this reason, in 1999 three weighing lysimeters were installed in the experimental farm "Las Tiesas" located in Albacete (Central Spain). The facility has a lysimeter for measuring the grass reference evapotranspiration (ET_o), a second for rotating annual crops and third installed in a perennial vineyard for measuring grape water use. Each of lysimeter is surrounded by a one hectare square buffer plot planted to the lysimeter crop. The lysimeters are weighed with a balance beam and load cell configuration, with most of the weight being eliminated using counterweight. The overall resolution of the systems are 250 g or 0.04 mm of water. The measurement frequency is one second, and a reading is registered by a datalogger every 15 min. During the period 2002–2003 the FAO-56 Penman-Monteith (FAO-56 PM) and the ASCE "standardized" version of Penman-Monteith (ASCE PM) hourly equations were evaluated by comparing them with reference lysimeter measurements. In 2003 we measured the water use (ETc) of broccoli as a double crop. Records of grapevine ET were collected from 2002 to 2008 and detailed canopy development information was obtained from 2004 to 2008 growing seasons. In this paper, we present results of grapevine ET measured by a weighing lysimeter during 2008 growing season.