A COMPARISON OF GROWTH RATES AND PHOSPHORUS DISTRIBUTION IN A RANGE OF PASTURE SPECIES

Relative growth rates (RGR) of nine annual pasture species and lucerne were compared in two experiments. During the first 4 weeks of growth the RGR of the clovers tended to be slower than that of the herbs and grasses, especially at low levels of applied phosphate. This situation was reversed towards maturity. Slow RGR of the tops of the clovers at low phosphorus levels was associated with the development of large root systems relative to tops; but at least in subterranean clover, the RGR of the roots was also slow. Other associated characteristics of the clovers, a month from emergence and at low phosphorus levels, were low phosphorus concentrations in the tops relative to nonlegumes, and a low proportion of their total phosphorus in the tops. The phosphorus content per unit weight of clover roots was low under these conditions. Differences between species in early growth rate were maintained on different soils, even though the soil solution contained widely different concentrations of phosphate. Establishment of species in the field, particularly during the seedling stage, is discussed in relation to growth rates at low and optimal levels of phosphorus. © 1969 CSIRO. All rights reserved.