ISHS Acta Horticulturae 664: IV International Symposium on Irrigation of Horticultural Crops
SOURCES OF UNCERTAINTY IN IRRIGATION SCHEDULING, AND PRACTICAL WAYS TO RESOLVE SOME OF THEM |
| Author: | A. Naor |
| Keywords: | irrigation scheduling, deciduous trees, water stress indicators |
| Abstract:
There are gaps between the scientific understandings of the factors affecting irrigation scheduling of deciduous trees and the day-to-day practice in commercial orchards. Growers are able to account for the day-to-day variations in evaporative demand by the use of the daily potential evapotranspiration (ETp) of a reference crop. In addition, there are sets of crop coefficients – the ratio between the evapotranspiration of a non-stressed crop and ETp – which reflect the seasonal dynamics of the amount of light intercepted by the canopy and of leaf conductance in a specific crop. Growers should be aware of uncertainties inherent in the evaluation of the following site-specific parameters: irrigation efficiency, which is affected by the combination of soil type, soil depth, irrigation equipment and irrigation regime; light interception by the canopy, which may change with variety, rootstock, training system, and with sub-optimal soil and climatic conditions; tree water consumption as affected by crop level; the effect of crop load (a measure of the ability of the canopy to support a certain crop level) on the threshold of water stress. The basic irrigation levels should be adjusted empirically to account for these uncertainties, by reference to water-stress indicators. The sensitivity of a few water-stress indicators to changes in moisture availability, and their inherent variability are discussed. A procedure for comparing water use efficiency (WUE) between plots within an orchard involves plotting the average fruit size in each plot, against the annual irrigation level per unit of yield weight in excess of the threshold level for producing any commercial yield. The potential use of decision support systems for irrigation scheduling is discussed. | |
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