Evapotranspiration, yield and water use efficiency of drip irrigated corn in the Bekaa Valley of Lebanon

We measured and compared evapotranspiration (ET) of a cor hybrid in 1998 and 1999 under full and deficit irrigation at Tal Amara Research Station in the Bekaa Valley of Lebanon, and studied differences in growth, yield and water use efficiency (WUE). In both years, corn was planted in May and harvested in September in two different fields of 2200 m(2) each, containing drainage lysimeters to directly measure ET. Irrigation differentiation was made upon crop evapotranspiration measured on the lysimeters, water was then applied at 100 and 60% of ET. Full irrigation treatment (I-100) was managed for high productivity, whereas deficit irrigation treatment (I-60) was maintained at 60% of field capacity. Water stress was applied continuously during the growing cycle. Seasonal ET reached on the lysimeter amounts of 952 and 920 mm, in 1998 and 1999, for total growing cycles of 128 and 120 days from sowing till harvest. Peak daily ET rates exceed at anthesis the evaporation of pan class "A" (some >14mm per day) and were not appreciably year-different when fully irrigated although seasonal ET was less in 1999. Leaf area index and dry matter decreased in the I-60 treatment. Leaf area index (LAI) was slightly higher than 7.0 in 1998 and nearly 6.0 in 1999 in the I-100 treatment. However, LAI decreased in both years by more than 25% in the I-60 treatment. Grain yield on a dry basis declined in 1998 from 1520 g m(-2) on the lysimeter to 1450 g m-2 on the full irrigated treatment to 1080 g m(-2) on the water deficit treatment. In 1999, these reductions ranged from 1340 g m(-2) on the lysimeter to 1280 and 1040 g m(-2) on I-100 and I-60, respectively. Total aboveground dry mater was also reduced by water stress. In 1998, a reduction of 130 g m(-2) was observed at harvest in I-100 in comparison with the lysimeter, while the reduction on I-60 exceeded 800 g m(-2) when compared to I-100. In 1999, these reductions were 100 and 400 g m(-2), respectively. Grain-related water use efficiency (WUEg) of lysimeter grown plants was 1.52kgm(-3) in 1998 and 1.34 kg m(-3) in 1999. However, fully irrigated corn had a WUEg of 1.68 kg m(-3) in 1998 and 1.54kg m(-3) in 1999. Higher WUEg values of 1.88 kg m(-3) and 1.87 kg m(-3) were obtained in 1998 and 1999, respectively, from the I-60 treatment. On a biomass basis, I-100 treatment had values of water use efficiency (WUEb) of 3.16 and 2.46 kg m(-3) in 1998 and 1999, respectively, while the I-60 treatment had values of 3.23 and 2.97 kg m(-3), respectively. On the lysimeter, these values were 3.0 and 2.34 kg m(-3), respectively. Finally, results revealed that cultivar Manuel maintained high levels of dry matter partitioning to reproduction organs under the high temperature/low humidity conditions of the Bekaa Valley, which makes it suitable for semi-arid environments. (C) 2003 Elsevier B.V. All rights reserved.