The effect of defoliation on the regrowth and leaf area index of lucerne

Abstract

In recent years, much agricultural research has been directed towards maximizing pasture and crop yields. The determination of yield through the growth and development of the forage crop plant is very complex. It involves the effects of a number of external factors on all the physiological processes of the plant, interactions among these processes, and their dependence on the internal factors governing the genotype of the plant. Therefore, to achieve maximum yields factors limiting growth must be identified and then overcome. The ability of a plant community to intercept light energy is of paramount importance in influencing its productivity under field conditions. In fact, light may be the factor governing the ultimate yield of any particular genotype or plant community. Since solar radiation must be intercepted by plants instantaneously, or it will be lost as a source of energy for photosynthesis, it is highly desirable to grow plants which are capable of utilizing light efficiently. Furthermore, it is desirable to devise management systems which will assist such plants to express their full growth potential under the conditions prevailing. Lucerne has become increasingly important as a forage crop in recent years as it has shown a potential for high yields of good quality feed under a wide range of conditions. The aim of the two field experiments described in this thesis was to add to our knowledge of the growth potential and growth pattern of defoliated lucerne and, if possible, to suggest how high production can be obtained under farm conditions. Measurements of light transmission and leaf distribution with height above the ground were made in an attempt to compare light utilization of lucerne with that of other agricultural crops. A summary of the results and the conclusions derived from them are given in the main part of this thesis. Tables of primary data and statistical analysis may be found in chronological order in the Appendices.