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Introduction. The aim of this work was to study the effects of regulated deficit irrigation (RDI) on fruit yield, fruit weight and fruit quality parameters, as well as soil-plant water relations, in apple orchards under high-frequency subsurface drip irrigation in a region with a continental climate. Materials and methods. Four irrigation treatments were applied in 2010 and 2011 to apple trees cv. ‘Gala’: T1, no irrigation; T2, optimal irrigation except during summer; T3, optimal irrigation except during summer when RDI with a threshold for irrigation at –1.2 MPa midday stem water potential (Ψ stem) was utilised; T4, optimal irrigation. The soil water status and plant water status were followed over two growing seasons. Results and discussion. The irrigation treatments had no significant impact on fruit yield. However, compared with optimal irrigation (T4) and RDI (T3), the absence of irrigation in summer (T1, T2) induced low Ψ stem ( The RDI treatment saved 47% water compared with optimal irrigation without negative impacts on yield and fruit quality. In the temperate conditions of Switzerland, Ψ stem, as well as Ψ soil, are well adapted for scheduling RDI in apple orchards.

Four different regulated deficit irrigation treatments were applied in 8-year-old apple trees in field conditions, in Switzerland. Soil water and plant water status were followed in the different treatments, during about 100 days, from 40 to 140 days after full bloom and are reported. Our results show that in spite of clear differences in water status, there were no important differences in yields.

Inner and surface temperatures of several 'Golden Delicious' apples in orchard and air temperature were measured during more than 2 months. In addition to temperature measurements, the 3D canopy structure was measured to compute the light interception of each measured 'Golden Delicious' apple. From this we extracted quantitative information about fruit temperature dynamics and fruit temperature variability within a tree crown in relation to air temperature fluctuations and fruit sunniness. Especially, fruit temperature dynamics were analyzed at daily and monthly time scales and compared to the air temperature dynamics. Results showed that when an averaged fruit per tree and a daily time scale were considered, as it is commonly done in fruit or pest development models, fruit temperature was equal to air temperature. However, during daytime, large departure from air temperature and large inner temperature gradients which could have significant effect on fruit physiological processes were measured. Moreover, such departures were highly variable among fruits within a tree canopy. To explain such within tree variability, the light interception by fruits must be taken into account. From this experiment, useful relationships between fruit temperature, air temperature and fruit light interception for fruit physiological model were derived and explained from physical principles. (C) 2008 Elsevier B.V. All rights reserved.