Growth and Nodulation Response in Guar at Different Soil Moisture Levels and Post-Deficit Recovery Potential upon Moisture Restoration.

Guar (Cyamopsis tetragonolobus L. Taub) is an annual legume that is highly tolerant of hot and dry conditions and is grown in semi-arid environments of world, primarily for the industrial value of galactomannan (guar gum) derived from its seed endosperm. As a legume, producers hope for soil N credits through biological N fixation, which requires formation of root nodules, but speculations are that the nodulation in guar is poor and sporadic under dry conditions. Two replicated, and repeated greenhouse pot studies were conducted to assess the impacts of various moisture regimes on root nodulation and growth characteristics of guar. The first study evaluated static moisture conditions (100, 75, 50, and 25% ET replacement) in two soils (sandy loam and clay loam), while dynamic moisture conditions (100, 75, and 50% ET replacement, and 75 and 50% ET replacement relieved to 100% after 20 and 30 DAP) were evaluated in the second study. There was a direct positive relationship of increasing moisture availability on plant height, biomass and nodule weight, but no effects on nodule number and reproductive plant nodes. Results followed the similar trend for biomass and nodule weight between soil types but were inconsistent for plant height, nodes and nodule number. Based on the 100% ET control, study-2 showed high overall recovery averages across the lower moisture regimes for plant height (107.5 to 110%), biomass (89.6 to 116%), and nodule weight (84.5 to 106%) upon relieving to 100 % ET; the recovery values differed very little among the treatments (both the moisture level and timings) and there was no impact on nodule numbers and reproductive nodes. The Findings indicate soil moisture as a key factor influencing guar root nodulation, which may limit the potential N-benefits under limited moisture, but guar exhibited an excellent recovery potential with the moisture restoration.