EFFECTS OF SOIL NUTRIENTS AND MOSITURE ON ROOT/SHOOT RATIOS IN LOLIUM PERENNE L AND TRIFOLIUM REPENS L

The dry weights of foliage and roots (excluding stembases) were compared in a 33×22 factorial experiment with Lolium perenne L. and Trifolium repens L. grown in pots with three nitrogen (0-300 ppm N), phosphorus (0-300 ppm P), and soil moisture (pF 3.2, pF 2.4, and waterlogged) treatments, each duplicated.Root/shoot ratios were influenced significantly (P < 0.001) by N, P, and W (soil moisture), but these main effects were qualified by highly significant first-order interactions and second-order interactions which included N and P. The lowest R/S ratios occurred where N, P, and W were all non-limiting, and the highest where there was an imbalance of these factors.The explanation suggested is that a decrease in the availability of N, P, or W causes an increase in the relative weight of roots, but in the presence of N, P, or W deficiency an increase in any one of these factors causes a further increase in the R/S ratio by increasing the relative efficiency of the foliage. © 1969 OXFORD UNIVERSITY PRESS.