Deficit Irrigation on Guar Genotypes (Cyamopsis tetragonoloba (L.) Taub.): Effects on Seed Yield and Water Use Efficiency

For guar, a well-known drought and heat-tolerant industrial legume with a spring–summer cycle, limited research has been conducted into measuring the effects of drought on yield potential. A two-year field experiment was conducted to explore the effects of different irrigation regimes on yield, yield components and water use efficiency (WUE) on five cultivars of guar (Kinman, Lewis, Matador, Monument, and Santa Cruz) in a semi-arid Mediterranean environment. Three different water replenishment levels were used: fully irrigated (IH, 100% of the ET), and 50% (IM) and 25% (IL) irrigated. Seed yields ranged from 1.24 (IL) to 3.28 t ha−1 (IH) in 2011, and from 0.98 (IL) to 2.88 t ha−1 (IH) in 2012. Compared to IH, the two-year average seed yield reductions for IL and IM were 49% and 26%, respectively. Lewis and Santa Cruz showed significantly greater grain yields under fully-watered and water-limited conditions. The number of pods per plant achieved the highest positive direct effects on seed yield (r = 0.924***). The highest values of water use efficiency were observed in the IL water regime (1.44 kg m−3 with increments in improved water use efficiency of +34 and +95% when compared with IM and IH, respectively).