| For irrigation design and scheduling, water use of crops is commonly estimated from calculated grass reference evapotranspiration (ETo) multiplied by published crop coefficients (kc). This method is assumed to adjust crop values in different climates.; However, the simple application of kc may not be accurate in cool, humid climate, especially for tall crops well coupled to bulk air. The aim of this work was to measure actual water use in an apple orchard and vineyard in New York, and to test the values against published kc values. Measurements of water use in dwarf apple trees and vines were made with heat pulse and heat balance sap flow gauges calibrated with whole-canopy gas exchange chambers (to check or correct potentials errors related to the velocity-to-flow assumptions).; Daily ETo was estimated from meteorological data acquired nearby. Results suggest the inadequacy of using kc values directly from arid climates in cool and humid climates since published kc values generally overestimated the measured water use rates. Also, the crop coefficient concept implies that grass, orchards and vineyards behave the same in all climates; this does not seem to be true in cool humid climates. Grass-to-tree/vine differences in advective flows, boundary layer conditions and stomatal regulation appear to result in varying ET ratios. Modifications that take into account the specific characteristics of apple tree and vine canopy, such as light interception and stomata regulation by environmental factors, were used to adapt a general formulation of Penman-Montieth equation to the orchard and vineyard case. Results are in good agreement with field measures, although overestimations can arise during periods when internal plant factors or other stresses may reduce stomata conductance. |
