EFFECTS OF SOIL-MOISTURE DEFICITS ON THE WATER RELATIONS OF BAMBARA GROUNDNUT (VIGNA-SUBTERRANEA L VERDC)

The components of leaf water potential (Psi(1)) and relative water con tent (RWC) were measured for stands of bambara groundnut (Vigna subter ranea) exposed to three soil moisture regimes in controlled-environmen t glasshouses at the Tropical Crops Research Unit, Sutton Bonington Ca mpus, Treatments ranged from fully irrigated (wet) to no irrigation fr om 35 days after sowing (DAS) (dry). RWC values varied between 92-96% for the wet treatment, but declined from 93% to 83% in the dry treatme nt as the season progressed, Psi(1) at midday decreased in both the we t and dry treatments, but the seasonal decline was more pronounced in the latter: seasonal minimum values were -1.19 and -2.08 MPa, respecti vely, Plants in the wet treatment maintained turgor (Psi(p)) at about 0.5 MPa throughout the season, whereas values in the dry treatment app roached zero towards the end of the season, There was a linear relatio nship between Psi(p) and Psi(1), with Psi(p) approaching zero at a Psi (1) of -2.0 MPa. Mean daily leaf conductance was consistently higher i n the wet treatment (0.46-0.79 cm s(-1)) than in the intermediate and dry treatments (0.13-0.48 cm s(-1)). Conductances in the intermediate and dry treatments were similar, and the lower evapotranspirational wa ter losses in the latter were attributable to its consistently lower l eaf area indices (L): L at final harvest was 3.3, 3.3 and 1.9 for the wet, intermediate and dry treatments, Bambara groundnut was apparently able to maintain turgor through a combination of osmotic adjustment, reductions in leaf area index and effective stomatal regulation of wat er loss.