THE GROWTH OF LUPINUS SPECIES ON ALKALINE SOILS

Lupinus angustifolius L. grows poorly on alkaline soils, particularly those that are fine-textured. This poor growth has been attributed to high concentrations of bicarbonate, high clay content and/or iron defi ciency. In field studies, we examined the growth of 13 lupin genotypes reliant on N-2 fixation, or receiving NH4NO3, at four sites with vari ous combinations of soil pH and texture.Plants grown on an alkaline cl ay and an alkaline sand showed iron chlorosis at early stages, and had a slower shoot growth than those grown on an acid loam or an acid san d. Species varied greatly in the severity of iron chlorosis and also i n growth and seed yield, with L. angustifolius, L. luteus and L. albus more affected than L. pilosus, L. atlanticus and L. cosentinii. Ranki ngs of growth and seed yield of the lupin genotypes on the alkaline cl ay correlated well with the rankings on the alkaline sand soil. Plants which had severe iron chlorosis in alkaline clay also had severe chlo rosis in alkaline sands. However, correlation between the severity of iron chlorosis and early shoot growth was poor. The results suggest th at high pH and/or high bicarbonate are more likely than soil texture t o be the primary factors restricting the growth of commercial lupins.