Guar resilience in water-restricted production

Guar [Cyamopsis tetragonoloba (L.) Taub] is an alternative crop in the Southern High Plains that thrives in semi-arid regions, due to its low water input requirements. Field experiments were conducted in 2017 and 2018 at New Deal, TX, to evaluate the response of guar (`Matador') to four levels of deficit irrigation (DI; extreme, 51 mm; severe, 127 mm; moderate, 203 mm; and mild, 279 mm). Soilmoisture extraction patterns, plant height, leaf area index, yield components, seed yield, harvest index (HI), agronomic water use efficiency (AWUE), and irrigation WUE (IWUE) were measured among the irrigation levels. In both years, guar grown under extreme and severe DI extracted a major portion of the water from the 50-to-100-cm soil depth. Water deficit reduced plant height, leaf area index, and number of pods per plant in both years. However, the IWUE and 1,000-seed weight increased with reduced irrigation. There were no significant differences in seed yield, HI, and AWUE among treatments as a result of a tradeoff between increased seed weight with low pod production under lower DI treatments and increased pod production with low seed weight under higher DI treatments. Guar extracted water deeper in the soil and produced adequate numbers of pods per plant in balance with the source organ capacity to allocate resources toward optimal seed development. Our research offers valuable information about root exploration and development of larger seeds as compensatory mechanisms that can be further explored to improve the adaptability of guar under water-restricted production conditions.