Field studies on nodulation and growth of Centrosema pubescens Benth.

Abstract

Field growth and nodulation of Centrosema pubescens in northern and southern Queensland have been studied. Plant growth has been considered in terms of yield, growth rates, net assimilation rates, and leaf area indices. The yields followed a sigmoid curve. Growth rate and net assimilation rate increased to a maximum at the time of stolon production. While the growth rate was maintained at this level until winter retardation and recession of growth, net assimilation rate continually declined following stolon production. Net assimilation rates in northern and southern Queensland were similar. Winter retardation of growth occurred when minimum screen temperatures were below 55 deg. F. and maximum screen temperatures below 78 deg. F. A periodicity in nodulation was observed. Nodulation continued throughout growth. Following stolon formation nodulation occurred on stoloniferous roots, while there was a progressive elimination of older nodules on the tap-root system. There was no indication of a progressive elimination of smaller nodules. Nodulation and nodule senescence are considered to be governed by vegetative growth of the plant rather than other plant factors such as flower production. Nitrogen analyses showed that only a small proportion of the plant nitrogen is contained in the nodules and only 4-20 per cent. in the underground parts. Cutting to simulate heavy grazing resulted in a loss of two-thirds of the plant roots by weight and inactivation and sloughing of a major proportion of the nodules.