Effects of Soil Nutrients and Moisture on Root/Shoot Ratios in Lolium perenne L. and Trifolium repens L

The dry weights of foliage and roots (excluding stembases) werecompared in a 3³x2² factorial experiment with Lolium perenneL. and Trifolium repens L. grown in pots with three nitrogen(0–300 ppm N), phosphorus (0–300 ppm P), and soilmoisture (pF 3.2, pF 2.4, and waterlogged) treatments, eachduplicated. Root/shoot ratios were influenced significantly (P < 0.001)by N, P, and W (soil moisture), but these main effects werequalified by highly significant first-order interactions andsecond-order interactions which included N and P. The lowestR/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 availabilityof 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 inany one of these factors causes a further increase in the R/Sratio by increasing the relative efficiency of the foliage.