Transpiration of Grapevines in the Humid Northeastern United States

Abstract

For irrigation design and scheduling, water use of crops is commonly estimated from grass reference evapotranspiration (ET₀) estimates multiplied by published crop coefficients (k_c). This method is assumed to stabilize k_c across climates because of the response of ET₀ to meteorological variables. However, the simple application of reference grass-based k_c models may not be accurate in a cool, humid climate, especially for sparse and tall crops where stomatal regulation is well-coupled to bulk air and sensible and latent heat exchanges may have a different dynamic than in grass. The aim of this work was to measure actual transpiration in a vineyard in the humid climate of New York and compare the results with the estimates obtained using the reference grass-based crop coefficient model. Measurements of water use in Concord grapevines (Vitis labruscana Bailey) were made with heat-balance sap-flow gauges calibrated against canopy gas exchange chambers. Daily ET₀ was estimated from meteorological data acquired by a nearby weather station. Daily transpiration rates per single vine ranged between 15 and 40 L day⁻¹, with hourly rate peaks of 4 L hr⁻¹. Water use declined during the hottest and driest part of the season, probably due to either water or heat stress. Results suggest that even in humid climates, grapevines might require irrigation occasionally. The reference grass-based k_c was inadequate to quantify the degree of coupling between stomatal regulation of transpiration and bulk air conditions, specifically vapor pressure deficit. Overall, results suggest the necessity of developing crop-specific models for water management.