A study of growth in lucerne in response to defoliation

In many areas lucerne has become increasingly important as a forage crop. In the past lucerne was used largely as a hay or silage crop. The result is that research has been concentrated mainly on aspects of management which would give maximum yields or high-quality feed, e.g. the stage at which the crop should be cut for hay on the basis of stage of flowering, the appearance of basal shoots, or accumulation of root reserves. With the increase in acreages established to lucerne, especially in areas which cannot support more mesic leguminous species, its uses have now been extended. No longer considered merely a hay crop, it is being used to an increasing extent to provide pasturage. Practical problems which have arisen are the necessity to assess the effects of grazing and haying and combinations thereof, and to determine how grazing can be incorporated with the management of the stand for hay to greatest advantage. In this series of experiments, therefore, grazing and haying have been simulated in an attempt to assess the yield of lucerne in response to heights and frequencies in various combinations. In recent years studies on the growth of pasture plants have reflected an increasing tendency to turn away from exclusively empirical experimentation towards more basic research. In this way it has become possible to explain the causes as well as to establish the effects brought about by certain treatments. The value of this approach is obvious, for once the factors governing the expression of a treatment effect are known, it should be possible to reproduce within limits any desired effect. In fodder crops, the growth analysis technique is well suited to such investigations. Precise measurement of growth in response to defoliation may be expected to provide information on the reaction of the plant to treatment under different environmental conditions and thus suggest how maximum production might be obtained. The aim of the series of experiments reported within was, therefore, to determine the effects of defoliation treatments on the growth of lucerne, and if possible the reasons for these effects. The investigations took the form of two pot experiments which served as a basis for a field experiment. An experiment in the growth cabinet followed in order to clarify some details which had arisen. The results indicated the importance of both frequency and height of cut in determining yields, while an analysis of the growth of lucerne suggested reasons for its success as a high-producing fodder crop. In this dissertation, all tables of basic experimental data and analysis of variance tables may be found in chronological order in the Appendices, and will not be referred to in the text.