Appraisal by Numerical and Statistical Techniques of the Interaction of Moisture Stress and Phosphorus in the Development of the Tropical Legume Macroptilium atropurpureum (Dc.) Urb

Abstract

The interaction of two levels of soil moisture and four levels of phosphorus on the development of Macroptilium atropurpureurn was studied for 18 harvests at 2-day intervals beginning on day 29 after sowing. Variates studied were fresh weight. dry weight, nitrogen and phosphorus contents for the laminae. stem plus petioles, root and nodules. The responses to treatment of these variates were shown by preliminary analyses of variance to contain complex patterns of interaction. The important facets of these interactions were then appraised by an extension of the usual univariate methods and the overall pattern of the interaction was delineated by a classificatory analysis. On the basis of the 14 attributes studied, there were six groups of responses to treatment. The lowest of these groups corresponded to failure to grow at low levels of phosphorus. The next group represented the response of nodules to treatment. Subsequent groups represented higher growth potential following efficient functioning of the nodules. Effects on nodulation were thus primary to subsequent patterns of plant development. Water stress greatly impaired both plant and nodule development, particularly at the higher two levels of phosphorus, whereas active growth occurred in normally watered plants. At these two phosphorus levels the effect of water stress was on development rather than on chemical composition, there being large absolute but small relative effects on chemical data. The lower levels of phosphorus supply contrasted with the two higher levels in having much lower rates of growth and of water loss.