The interactive effects of phosphorus, potassium, lime and molybdenum on the growth and morphology of white clover (Trifolium repens L.) at establishment

The effects of simultaneously varying P, K, lime and Mo supplies on the gro wth and shoot morphology of white clover (Trifolium repens) at establishmen t were investigated in a factorially designed glasshouse experiment. Phosph orus and lime applications had almost identical, additive, effects on dry-m atter (DM) production, and if was clear that the benefit of both treatments lay in the resultant improvements in plant available P. The adverse effect s of P deficiency on young plants resulted, immediately, in a large decreas e in stolen branch numbers, but only when the deficiency became acute did s imilar declines in the dimensions of leaves and petioles occur. It was sugg ested that this preferential maintenance of leaf and petiole expansion proc esses under moderate P deficiency, by enabling white clover to retain favou rable upper canopy positions, could be an ecological adaptation to maximize its chances of survival in mixed grass-clover swards. Unlike P, It had lit tle effect on clover growth or shoot morphology. However, there was some ev idence that plants suffering from acute K deficiency preferentially partiti oned resources to organs associated with exploratory growth, i.e. to stolon s, at the expense of the plant's photosynthetic capability. Molybdenum appl ication had no effect on DM production or shoot morphology, but did improve the N status of shoots, presumably by enhancing N-2 fixation. It was concl uded that the survival of white clover in swards at establishment is critic ally dependent on P supply, and that one of the main benefits of liming is the resultant improvement in P availability.