PREFACE

The Symposium ran for five days from 27th to 31st May 1996. There were four days of plenary lectures, oral and poster sessions. One day was devoted to a field trip where the participants could visit a modern fruit tree farm and discuss, in situ, with agronomists and growers, about the local and general problems related to fruit production.

Plenary lectures took place at the Aula Dei Campus, located 13 km north of downtown Zaragoza. This City, founded over a two thousand years ago, is very much a modern site appreciated for an active cultural life, with many of its 685,000 inhabitants serving education, administration, industry and commerce. It is also the focus of an important fruit tree growing area.

The Aula Dei Campus was founded in 1944, after the setting up of the Estación Experimental de Aula Dei of the Consejo Superior de Investigaciones Científicas (CSIC), which was the starting point for the development of a series of facilities and operations to serve agriculture which comprise research, extension, application and advanced training: a) Office of CSIC in Aragón; b) Aula Dei Experimental Station (CSIC); c) Institute for Pyrenean Ecology (CSIC); d) Agricultural Research Service of the Autonomous Government of Aragón (SIA-DGA); e) Mediterranean Agronomic Institute of Zaragoza of the International Center for Advanced Mediterranean Agronomic Studies (IAMZ-CIHEAM).

The aim of this Symposium was to bring together scientists from a broad range of disciplines related to fruit tree nutrition, providing them opportunities to exchange new knowledges, ideas, experiences and techniques and also to promote the collaboration among scientists. These objectives were reached by the development of the following topics: Physiological and biochemical aspects of plant nutrition; Genetic, environmental and cultural factors affecting tree nutritional status; Plant and soil analyses and their interpretation; Soil conditions and management of growth media affecting tree nutritional status; Mineral element deficiencies or excesses: diagnosis and correction; Nutrient requirements and fertilizer recommendations in relation to crop quality and environmental protection.

A volume was elaborated containing all relevant information concerning the Symposium (location, climate, history, etc.) and 115 abstracts including communications and plenary lectures.

The interest and importance of the Symposium was endorsed by the most important regional authorities attending the Opening Ceremony.

Along the scientific sessions, 6 invited overview lectures, 35 oral communications and 52 posters were presented and discussed by 116 delegates from 23 countries. This Book of the Acta Horticulture Series is the result of the manuscripts received and accepted after evaluation by the Editorial Board. For the rest of contributions, only the abstracts have been included.

The productivity of fruit crops is conditioned by three major factors: plant material characteristics (rootstock and scion), nutrient supply (manuring, fertilizers and soil characteristics) and cultural practices (chemical treatments, thinning, pruning, water supply). All these factors are closely related as it has been demonstrated by the results presented in this Symposium. On the other hand, as was also reported, the objective of modern fruit production, is not only to achieve a maximum yield, but the highest fruit quality with the less environmental impact.

Genetical studies, are needed to direct tree breeding towards new plant materials, cultivars and rootstocks, allowing the grower to make profits from an orchard managed according to proper cultural practices, known only after long term observations of their effects. As a consequence, new varieties and rootstcks imply new nutrient requirements and therefore the recalculation of reference values for leaves or other organs, and also new sampling times should be explored. On the other hand, a recalibration of different soil testing methods could be recommendable taking into account the peculiar genetical characteristics of plant material and the environmental conditions of the different growing areas.

Mineral nutrients have functions as constituents of organic structures, as activators of enzyme reactions, or as charge carriers and osmoregulators; therefore, the nutritional status of plants will affect growth and development. In addition, considering the use of deciduous fruits as human foods, the intake of nutrients (minerals, sugars, proteins, and vitamins) throughout the fruits is of increasing significance to avoid malnutrition of people. Some studies were focused on the achievement of high yield and good quality by an adequate mineral nutrition of the plants.

It is obvious that in deciduous fruit production, the physiological and biochemical roles of the various mineral elements are often not well considered; in practice, there are uncertainties with the recommendations or they are not well defined. Thus, there is still a great necessity for applied research on optimal mineral nutrition of fruit trees (and as a consequence also on adequate fertilizer application) to make fruit production economically competitive. Under the same approach, biochemical diagnosis including enzymatic assays respond to the criteria of essentiallity for a single nutrient, because the activity or functional role of some metabolites can vary considerably for a small nutrient alteration.

Qualitative techniques as visual diagnosis are sometimes very helpful to detect individual problems, but when visual symptoms are noticed, some reduction in yield has been already caused. Quantitative methods are preferred, being foliar analysis the most widely used, since the main metabolic and photosynthetic processes take place in the leaf; consequently, its particular composition reflects the nutritional balance of the whole plant. However, the complexity of nutrient movement inside the tree and the plurality of supply sources cannot be reflected by the sole leaf analysis, which only provides a limited pattern of either nutrient needs or nutrient status. Improvement of the accuracy of tissue analysis as an approach to diagnose deficiencies or excesses will be aided by new technologies.

Increasing social concern regarding environmental issues in orchards is presently manifested mostly by the negative consequences of excessive N fertilization resulting in contamination of groundwater. Although concerns for P, Ca, B, and Zn applications are not so significant, it will be necessary in future to improve understanding of environmental consequences about the application of all fertilizer materials, for an efficient and economical use in intensive production systems.

As a consequence of the above considerations and findings presented to this Symposium we could propose the following alternative topics as future investigations which results could be discussed during the next International Symposium to be held in Summerland, Canada (August, 2000): 1.- Soil conditions and management practices in relation to fruit tree nutrition and fertilizer supply; 2.- Water supply and nutrition: fertigation norms adapted to the particular conditions of the fruit orchards; 3.- Rational fertilizer use to decrease economical inputs with the less environmental impact; 4.- Organic matter supply: wastes, sewage sludges, slurries, farm manures, and other organic residues. Effects and risks; 5.- Analysis of other organs as new plant materials for nutritional diagnosis; 6.- New proposals for nutritional indexes and their interpretation. Regional studies; 7.- New studies on the nutritional behaviour of scion/rootstock combinations, and new techniques of plant multiplication and nutrients supply; 8.- Biochemical and physiological aspects of mineral disorders: diagnosis and correction; 9.- Early diagnosis of nutritional status: preventive norms to avoid deficiencies and/or imbalances; 10.- Influence of mineral elements on fruit quality and postharvest behaviour; 11.- To take into consideration the inclusion of soft fruits, olive, nuts and perhaps forestry species, as a matter of interest for the next Symposium

The Organizing Committee thanks the authors for their contributions and appreciate the interest and scientific value of the presented works that made possible the success of the Symposium. We look forward to have the opportunity to continue sharing knowledges and discussing results in the next meeting to be held in Canada.

Zaragoza May, 1997

The Editors