The promotion of winter growth in pastures through growth substances and photoperiod

Abstract

The effects of growth substances and extended photoperiod on the growth rate of phalaris-annual grasses-subterranean clover pastures were studied at Canberra in the winter of 1964. Responses to applications of 4 and 20 g gibberellic acid (GA) per acre differed for June and July applications. All available data on GA responses on this pasture type were collated. Responses to GA increased with decreased growth rate of normal pasture. Thus a sixfold increase in growth rate was obtained when the normal growth rate was 2 lb dry matter/acre/day. Responses were independent of dose rate (from 1 to 105 g GA per acre) or time of application. Responses to GA were obtained subsequent to the first harvest. The length of time during which cumulative growth on GA-treated pastures exceeded that on normal pastures was related to the growth rate of the normal pastures. The response in growth to 4 g GA could be increased to the level of that obtained with 20 g GA by the addition of either 4 g naphthylacetic acid or 4 g kinetin. Phalaris showed greater response to GA than did annual grasses or subterranean clover. Extending the photoperiod to 16 hr gave a 40% increase in growth rate in winter. This was associated with earlier floral initiation whereas increases in growth rate induced by growth substances were not. These results are discussed in relation to increasing plant and animal productivity in year-round grazing systems.