Journal of Agricultural Science, Cambridge (1996), 126, 307-318. © 1996 Cambridge University Press 307 Growth, development and yield of bambara groundnut ( Vigna subterranea) in response to soil moisture S. T. COLLINSON, S. N. AZAM-ALI, K. M. CHAVULA AND D. A. HODSON Department of Agriculture and Horticulture, University of Nottingham, Sutton Bonington Campus, Leics LEI2 5RD, UK (Revised MS received 18 May 1995) SUMMARY Stands of bambara groundnut (Vigna subterranea (L.) Verde.) were grown in five controlled- environment glasshouses at the Tropical Crops Research Unit, University of Nottingham, Sutton Bonington Campus, in 1990. Five soil moisture regimes were imposed (one per house), from fully irrigated each week (treatment A), to no irrigation after crop establishment at 35 days after sowing (DAS) (treatment E). Decreasing the amount of water applied resulted in a decline in total dry matter production and harvest index, and a reduction in pod yield from 412 (treatment B) to 0041 ha" 1 (treatment E) at 125 DAS. A maximum leaf area index of 5-4 was achieved by treatments B and C at 90 DAS, resulting in a fractional interception of c. 0-8 of incoming radiation. Total accumulated radiation interception values were 749, 693, 688, 618 and 554 MJ m~ 2 for treatments A, B, C, D and E, respectively. The efficiency of conversion of the radiation intercepted into dry matter was reduced from 1-41 to 0-50 g MJ" 1 by drought. INTRODUCTION Although botanists estimate that there are > 350000 plant species, as few as 17 species provide 90% of mankind's food supply (Stoskopf 1985). Considerable effort has been devoted to improving the productivity of these major crop species but there remains a largely unexplored potential in many crop species which have been grown locally for centuries. Evaluating these under-utilized species by conventional methods of breeding and field trials is slow and manpower intensive, and scarce research funds are rarely directed towards long-term research on such crops of unknown potential. Furthermore, because many of these crops are grown by small-scale subsistence farmers, little effort has been devoted to assessing their nutritional and economic value. The problems of assessing the viability of any crop through routine field trials are compounded by the vagaries of local weather conditions and the variability of soils and climates from place to place. An alternative strategy, before advocating extensive field experiments, is to assess the salient physiological features of potentially useful species using controlled environments, in which principal factors such as daylength, temperature, and soil and atmospheric water can be adjusted across a pre-determined range. In this way, key physiological attributes can be identified to define the types of agricultural environ- ments and agronomic practices that are likely to be suitable for a given species. If these initial studies confirm that a particular species has promise, a more clearly focused series offieldexperiments can then be initiated. Bambara groundnut Bambara groundnut (Vigna subterranea (L.) Verde, syn. Voandzeia subterranea (L.) Thouars) is an indigenous African legume grown mainly by sub- sistence farmers in much of semi-arid Africa. In many of these regions, it ranks third in importance after groundnut (Arachis hypogaea L.) and cowpea (Vigna unguiculata (L.) Walp) (Sellschop 1962). Previous reports indicate that the mature seeds are a rich source of protein (16-25% DM) and carbohydrate (42-60% DM) but, in comparison with groundnut, the lipid content is low (5-6% DM) (Poulter & Caygill 1980; Aykroyd & Doughty 1982; Deshpande & Damodaran 1990; Brough & Azam-Ali 1992). Although bambara groundnut will often yield in environments which may be too hostile for more favoured legumes, such as groundnut, there are few reports of its productivity in relation to the capture and use of resources such as solar radiation and soil moisture. Nevertheless, the species is reported to possess many valuable traits such as promiscuous