Agronomic and Economic Performance of Supplementary Irrigation for Winter Cereals and Legumes in the Beqaa Valley, Lebanon

Abstract

Climate variability and macroeconomic instability are placing unprecedented pressure on rainfed agriculture in the Eastern Mediterranean, where erratic precipitation, rising energy-driven irrigation costs, and volatile commodity prices threaten the viability of strategic winter crops. This thesis evaluates whether supplementary irrigation (SI) of winter cereals (barley, wheat, triticale) and food legumes (lentils, chickpeas) is both agronomically effective and economically defensible under the climatic and market conditions of Lebanon’s Beqaa Valley. Across two consecutive growing seasons (2021/2022 and 2022/2023), paired rainfed (control) and SI plots were managed under real-farm operational conditions on a clay-textured site, with cereals receiving 100 mm (1,000 m3/ha) and legumes 66 mm (660 m3/ha) of sprinkler-applied water during reproductive stages. Grain and hay yields, full input-cost accounting, and prevailing local prices were integrated to quantify gross revenues, net profits, and the Economic Irrigation Water Productivity (EIWP) — defined as the incremental net economic return per cubic meter of irrigation water beneficially applied. The two seasons differed sharply in both climate and market context: January 2023 received only 2.7 mm of rainfall compared with 110.1 mm in January 2022, and grain and hay prices declined by 32–53% between the two years, providing a natural sensitivity test of the SI strategy. Across all five crops, SI consistently increased grain and hay yields, with the largest gains observed for cereals (barley grain yield, for example, rose from 3.29 to 6.18 t/ha in 2022). However, the economic outcomes diverged sharply from the agronomic ones. In 2022, SI generated positive Net EIWP for all cereals (barley: +US$1.04/m3; wheat: +US$0.73/m3; triticale: +US$0.32/m3) and a marginal gain for lentils (+US$0.013/m3), while chickpeas already returned a negative Net EIWP (– US$0.13/m3). In 2023, the combined effect of an early-season drought and a market-wide price collapse pushed wheat into negative territory (–US$0.04/m3), deepened legume losses (lentils: –US$0.60/m3; chickpeas: –US$0.19/m3), and substantially eroded barley’s gain (+US$0.19/m3). Barley was the only crop to maintain a positive Net EIWP across both seasons. These findings reveal a structural decoupling between agronomic productivity and economic profitability: higher yields under SI do not automatically translate into higher farm incomes when output prices fall or when energy-driven water costs rise. Profitability under SI in the Beqaa Valley is therefore conditional on three simultaneous factors — crop type, inter-annual climate (especially early-season rainfall), and prevailing commodity prices — rather than on water supply alone. The thesis recommends prioritizing SI for resilient cereals (particularly barley), adopting deficit or partial irrigation strategies for sensitivity-prone crops, transitioning toward lower-cost energy sources such as solar-powered pumping to reduce the marginal cost of water, and pairing on-farm decisions with market-stabilization and pricing policies. These integrated measures are essential for sustaining smallholder profitability and food-security cropping in semi-arid Mediterranean systems facing intensifying climatic and economic stress.