FOREWORD

It was decided to start the symposium with papers and discussion on the economics of high density planting. A unique feature of tree-crop system studies is the importance of the time factor and the need to make practical comparisons on a discounted cash-flow basis. It is only by economic analysis that the relative importance of planting costs, the number of years taken to reach a given level of yield, yield at maturity and costs of management (especially of controlling tree vigour) can be evaluated and systems differing in all these respects compared. Economic studies therefore not only show which systems are currently the most profitable but also how any given technological advance would alter the balance and which constraints must be overcome before the most productive systems can become the most efficient economically.

Having set the economic scene the next session dealt with biological and physical limits to system productivity: the effects of density of planting on the use of resources of sunlight, soil moisture and soil nutrients and on growth and yield per hectare.

In the third session research on methods of controlling tree growth and cropping so as to maximize the economic returns and utilize natural resources most effectively were considered. These methods include the use of dwarfing rootstocks and chemical treatments to induce early cropping and control vigour as well as methods of pruning, including mechanical pruning.

This was followed by a discussion of a number of integrated systems of high density planting, involving different combinations of plant material, chemical treatments and machinery, including the Long Ashton meadow orchard, the East Malling bed system and the New Zealand horizontal canopy orchard which is specifically designed for mechanical harvesting.

The main conclusions from the four sessions were reviewed in a final general discussion in which the potential contributions of plant breeding and engineering to high density systems for the future were also considered.

The papers are presented in this volume either as full length invited papers, which, considered together, were thought to outline the main areas of work on high density planting, or as abstracts of contributed papers which serve primarily to indicate which other important and relevant work is being carried out. The arrangement follows that of presentation in the symposium.

Perhaps the dominant feature of the symposium was the success of the multidisciplinary approach by which the range of expertise available from an international membership of horticultural scientists, economists, engineers and fruit growers was brought to bear on this central problem of fruit production. This integrated approach is clearly the key to devising relevant research programmes and applying the results in commercial practice. Visits to modern intensive commercial orchards in England and the Netherlands during the symposium confirmed the close relationship between research and practice in this area with many of the research findings of the last five years, eg the use of auxin paints to help control regrowth after pruning, being generally applied in English orchards.

A second distinctive feature of the symposium was its mobility. On-going work at East Malling, Long Ashton and Wilhelminadorp was seen by kind permission of their Directors and grateful thanks are due to them and to the fruit growers whose farms were visited. This mobility involved accommodation at Wye College, Churchill Hall, Bristol, Christchurch College, Canterbury, and near Wilhelminadorp. Special thanks are due to Dr. Cutting of Long Ashton for making the arrangements at Bristol and to Dr. Wertheim for the arrangements in Holland. My assistant, Miss Mary Schroeder, carried out much of the work relating to the main part of the meeting, the preparation and circulation of papers and the arrangements for transport and accommodation for which I am very grateful.

John E. Jackson