RELATIONSHIPS BETWEEN SHOOT AND ROOT CHARACTERISTICS OF WHITE CLOVER CULTIVARS DIFFERING IN RESPONSE TO PHOSPHORUS

Root dry weight and the relationship between shoot and root characteri stics for 119 white clover (Trifolium repens L.) cultivars and breedin g lines were examined at five (40, 120, 200, 400, and 500 mg P/kg soil ) phosphorus (P) levels. There were significant (P<0.01) differences a mong cultivars for root dry weight and root/shoot ratio. Instantaneous root/shoot ratio decreased with increasing P supply up to 200 mg P/kg , and then increased again from 400 to 500 mg P/kg soil. Allometric an alysis indicated that root growth relative to shoot growth increased w ith increasing P supply. There was a significant (P<0.01) cultivar x P level interaction such that for the cultivars, the root/shoot ratio w as either unaffected, increasing, or decreasing with increasing level of P supply. However, root/shoot ratio appeared to be unrelated to the functions used to describe the P response of the 119 cultivars studie d. Shoot characters such as dry weight, leaf number, and stolen length were most closely correlated with root dry weight at the moderately l ow P levels of 120 and 200 mg added P/kg, where average P response was 9 and 24% of yields at 500 mg P/kg soil, respectively, rather than at the higher P levels. Root/shoot ratio was significantly correlated (r >0.6) with root dry weight over all P levels but not with any of the m easured shoot characters (-0.2> r <0.3).