Sensing fruit and tree performance under deficit irrigation in 'September Bright' nectarine

In the face of increased demand for food combined with water scarcity under changing climate, improvements are required in irrigation management and orchard production systems to meet consumer expectations of high-quality fruit. This study examined fruit and tree performance of 'September Bright' nectarine under deficit irrigation in a modern high-density orchard. A deficit irrigation experiment was conducted over three consecutive seasons at Tatura, Australia. During fruit growth stage I, II and III, discrete irrigation levels were applied: 0, 20, 40 and 100% of crop evapotranspiration (ET_c). Trunk diameter, leaf photosynthetic performance (efficiency of photosystem II), leaf fluorescence, leaf chlorophyll concentration, leaf conductance, canopy light interception and harvested fruit yield and quality (size, colour, sweetness, maturity) of individual fruit were measured. Our findings showed that deficit irrigation had a significant effect on these fruit quality and tree parameters. Overall, at 40% ET_c regimes during stage II, yield and fruit quality were maintained, while yield and fruit size were reduced when the same regimes were applied in both stage I and III. More severe deficit levels penalised yield and fruit size, irrespective of fruit growth stage timing. Relationships between key fruit and tree metrics, physiological responses and utility of sensing instruments and platforms for precision orchard irrigation management are discussed.