FOREWORD AND PREFACE

The Fourth International Symposium on Irrigation of Horticultural Crops was held at the University of California, Davis in Davis, California (USA) from 1-6 September 2003 under the auspices of the International Society for Horticultural Science (ISHS). It was planned by members of the working groups (1) Water Supply and Irrigation, (2) Water Relations of Woody Crops and (3) Water Relations of Grapevines from Vegetable, Vine and Berryfruit Sections of ISHS. The UC Davis Symposium was organized by researchers from several Departments of the College of Agriculture and Environmental Science (CAES) and by scientists involved in earlier Symposia from France, Italy and Portugal. The convenor of the Symposium was Dr. Richard L. Snyder, Biometeorology Specialist for the University of California Division of Agriculture and Natural Resources. There were approximately 128 participants from twenty countries represented at the Symposium.

A Scientific Committee, which was composed of researchers from workgroups and other experts from several countries, selected 135 submitted abstracts for presentation. The presentation topics included (1) crop water requirements (measurements, modelling, soil-plant-atmosphere processes, and scaling transpiration) (2) plant water relations (ecophysiological interactions), (3) irrigation scheduling (scaling effects, applicability of methods), (4) water quality and environmental impact of irrigation (environmental impact of irrigation on water quality and vice versa), (5) irrigation systems, water management and productivity and (6) economics of irrigation (water transfers, economic optimization).

After the welcoming address from the convenor and the Vice Chair for the UCD Department of Land, Air and Water Resources Professor Kyaw Tha Paw U, Dr. Melvin Tyree from the USDA Forest Service presented the first keynote speech entitled -Drought Resistance: A concept without a measure! Where do we go from here to understand drought performance of ecosystems to crops?- Then, a second keynote speech entitled -FAO activities to develop agro-climatic datasets and tools for the needs of irrigation management- was presented by Dr. Michele Bernardi from the United Nations Food and Agriculture Organization in Rome. Each day of the Symposium there were one or two keynote presentations including: Dr. Theodore Hsiao -Selected aspects of crop water relations and evapotranspiration – What is known and what is not known?-, Dr. Richard Howitt -Economics of Water use in Agriculture-, Dr. Ramon Aragues -Challenges of conducting salt tolerance studies under field conditions-, Dr. Amos Naor -Practical implications in scheduling irrigation of deciduous trees- and Dr. Kyaw Tha Paw U -Evapotranspiration: Measuring and Modeling-. In addition, there were 84 submitted oral papers and 51 submitted posters, which are summarized in the following paragraphs. Several sessions emphasized the differential sensitivity of leaf and root growth to water stress, the underlying mechanisms to the responses and its importance for adaptation, the role of stomata in controlling canopy transpiration, coupling of the canopy and atmosphere, and photosynthetic water use efficiency in relation to variations in intercellular CO2 concentration and recent evidence on the importance of changes in CO2 concentration with humidity gradient in determining crop coefficients. These presentations provided a broad background on the current status of water relations research. However, they also showed the need for further research on partial root-zone drying/deficit irrigation (PRD), regulated deficit irrigation (RDI) and plant-based measurements to characterize water status. Generally, RDI studies investigated withholding irrigation water from crops to determine if the water stress can reduce water use while maintaining and improving marketable production. Many of the presentations discussed the use of leaf and stem water potential, trunk diameter fluctuations, etc. to quantify water stress and to improve marketable crop production. Presentations on PRD irrigation of apples, pears and grapevines generally emphasized the importance of accurate water status monitoring in conjunction with both RDI and PRD. Some papers indicated potential water savings with few adverse yield effects from using PRD, while others found little or no benefit from using the technique.

The evapotranspiration sessions showed that significant advances have been achieved in the ability to monitor and estimate ET using a variety of techniques. ET estimates were often related to crop canopy conditions, which provide useful information for those trying to improve irrigation scheduling and water resource planning. There were also oral presentations and posters on use of ET and/or soil monitoring for irrigation scheduling.

Another topic of the Symposium pertained to field response of crops to salinity. Precise determination of soil salinity and designing experiments for tolerance trials, using geo-referencing and salt-tolerance response models, were presented. Salinity effects on production of various crops were reported, showing that new findings may differ from earlier recommendations. For example, olive tree sensitivity to salts was found to increase with time of exposure to salty conditions, but pistachios were relatively insensitive to increasing salinity. In another experiment, most grass species were little affected by salty water.

In California, a shift towards planting higher value horticultural crops with a resulting increase in profits and more efficient use of the water was reported. Additional water needs are likely to come from trades and transfers that are mutually beneficial to buyers and sellers. However, restrictions on transfers might be needed to protect regional economies. Also, water quality is becoming a big issue due to the high cost for leaching of salts. In the future, horticultural production will likely change to improve the efficiency of water use.

During Friday afternoon, a business meeting was held to elect new chairs for two workgroups. Adriano Battilani, CER, Bologna, Italy was elected the new Chair for the Water Supply and Irrigation Workgroup (Vegetable Crops Section) and Ian Goodwin, Institute Tuchura, Victoria State, Australia was elected Chair of the Water Relations in Woody Crops Workgroup (Pome and Stone Fruit Section). A technical tour was held on Saturday, September 6, 2003. First, there was a visit to the UCD lysimeters, which were used in the development of ET equations, crop coefficients and many irrigation and water relations studies. The group then visited the CIMIS (California Irrigation Management Information System) weather station near the lysimeters. Then the tour continued to the Hines nursery near Winters, California to see a state-of-the-art irrigation system for a large nursery, designed to have minimal losses of drainage water. Following the visit to the Hines Nursery, the tour group went to the Wolfskill Pomology research farm near Winters, California to see the germplasm research plots and to have lunch. In the afternoon, the group visited an RH Phillips vineyard where an experiment to study air temperature cooling effects on wine grape quality was being conducted. Following the vineyard visit, the tour continued to the Nickels Ranch, where considerable research is conducted on irrigation management and water relations of tree crops. At the Nickels Ranch, W. Krueger, K.A. Shackel and L. Schwankl led discussions and demonstration on their research. All the participants contributed to the success of the Symposium. It was an important opportunity to exchange information and start new cooperation in the pleasant atmosphere of UC Davis Campus. The Fifth International Symposium is scheduled for 2007 near Melbourne, Australia (Convenor: Ian Goodwin) and the Sixth International Symposium is tentatively scheduled for 2011 in Talca, Chile (Convenor: Samuel Ortega Farias).

A link to a webpage summarizing the Irrigation Symposium can be found on the webpage: http://biomet.ucdavis.edu. Click on Symposium Summary under ISHS Irrigation Symposium to access the summary webpage.

Richard L. Snyder, Convenor

PREFACE The papers contained in this volume of Acta Horticulturae report the Proceedings of the IVth International Symposium on Irrigation of Horticultural Crops. Keynote speakers and authors of selected contributed oral and poster presentations were given the opportunity to submit a manuscript for publication. These manuscripts were reviewed by the symposium Editor and members of the Editorial Board. Only those papers judged suitable for publication following the authors consideration of reviewer suggestions appear in this volume of Acta Horticulturae. All papers were reviewed by two experts.

The ISHS acknowledges and appreciates the contribution of all editors and reviewers. They have made a significant contribution to improving the quality of this publication.

The ISHS Board of Directors