EFFECT OF SOIL NITRATE ON THE GROWTH AND NODULATION OF LUPINS (LUPINUS-ANGUSTIFOLIUS AND L-ALBUS)

The effect of increasing external nitrate (NO3-) concentration on the nodulation of Lupinus albus and L. angustifolius lines was examined in 2 sand culture experiments. In the first experiment 4 lines, 3 L. albus and 1 L. angustifolius, were grown at NO3- concentrations of 0, 2, 8, 16, and 30 mmol/L for 49 days. Increasing the NO3- concentration reduced nodule weight in all varieties to a similar extent. In a second experiment, 18 L. angustifolius lines were grown at NO3- concentrations of 2 and 8 mmol/L for 49 days. The ratio of nodule weights at the 8 and 2 mmol/L NO3- treatments varied widely, from 23 to 71%, between the lines. There appears to be potential for selection of L. angustifolius varieties able to maintain N2 fixation at increased levels of soil N.