Phosphorus levels in shoots of bambara groundnut in Botswana soils

The critical phosphorus (P) concentration and range of bambara groundnut (Vigna subterranea) plants were determined from a sand culture experiment at Botswana College of Agriculture. Twelve P levels (0.207-159 mg P pot(-1)) were used for growing the plants for 78 days (early podding stage) and the shoot P concentrations determined. The critical P concentration was used for assessing the P nutritional status of bambara groundnut plants grown in farmers fields in Botswana. Plants from 10 farmers' fields were sampled at 78 days after sowing and analyzed for P. The critical shoot P concentration and range for bambara groundnut determined visually from graphs were 0.15% and 0.15-0.20%, respectively. In 80% of the farms, plants showed shoot P concentrations between 0.10% and 0.13% which correspond with moderate to severe P deficiency. Therefore, most of bambara groundnut farmers in Botswana grow the crop under limiting P conditions.