THE CALCIUM NUTRITION OF BAMBARA GROUNDNUT (VIGNA-SUBTERRANEA (L) VERDC)

It is known that the calcium (Ca) requirement of the pods of groundnut (Arachis hypogaea (L.)) will be met by direct uptake of this element by the subterrean pods from the soil. In bambara groundnut (Vigna subt erranea (L.) Verdc.), however, some plants have been found to develop some of their pods above-ground. This suggests that the Ca supply of b ambara groundnut pods deviates from that in groundnut. Therefore, to e lucidate the Ca nutrition of bambara groundnut, with particular emphas is on the supply and internal distribution of Ca within the pod, three experiments were conducted consecutively, in which Ca supply to the r oots and pods of bambara groundnut was varied independently using a '' double-pot technique''. It appeared that calcium supplied to the poddi ng medium was not taken up by the pods. Hence the pods are completely dependent on Ca taken up by the roots. The total Ca accumulated in hul l and seed was found to be related to the dry matter mass of each of t he two pod compartments. It was found that the amount of Ca accumulate d in the pods was low compared with that of leaves. Within the pods, t he calcium concentration in hulls was significantly higher than that o f the seed. In all cases calcium concentrations in the seed were extre mely low, even when external Ca supply was abundant. This suggests tha t in bambara groundnut, Ca transport from the hull to the seed is the most limiting step in the supply of Ca to the seed.