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Crop load and irrigation interactions - a new dimension of RDI

Naor, A.
Acta horticulturae 2014 no.1038 pp. 113-119
apples, buds, canopy, crop yield, deficit irrigation, fruit quality, fruit trees, industry, irrigation rates, irrigation scheduling, olives, shoots, soil profiles, starch, stomatal conductance, water conservation, water potential, water stress, water use efficiency
Regulated Deficit Irrigation (RDI) was introduced to the fruit tree industry and improved the water use efficiency significantly. The rationale behind RDI is that the optimal tree water status is not necessarily a minimum water stress throughout the entire irrigation season. It allows saving water at certain phenological stages while maintaining canopy size and improving fruit quality. In addition, it may also optimize next season productivity by enhancing flower bud development. A new dimension of RDI, namely applying deficit irrigation when low crop load (the number of fruit per tree) is apparent will be presented in the following. The focus will be on demonstrating the importance of crop load in irrigation scheduling rather than reviewing the literature. Low crop load requires lower irrigation rates than high crop load in order to maximize commercial crop yield in apple and olive, but it seems as a general response in fruit trees. Crop load determines the demand for assimilates on a tree level (sink capacity) and irrigation affects the assimilation rate (source capacity). The combined effect of both of them determines the availability of assimilates which is reflected by shoot starch content in apple. Crop load alters the relationships between stem water potential and stomatal conductance which is more anisohydric at high crop load. This suggests that trees with high crop load may extract more water from the soil profile compared with those with low crop load. In spite of the adjustment of tree water relations by the crop load, higher water potentials should be maintained in order to maximize commercial crop yield from trees with high crop load.