Crop coefficients (Kc) developed from canopy shaded area in California vineyards
Larry E. Williams, Alexander D. Levin, Matthew W. Fidelibus
Abstract
Seasonal grapevine crop coefficients (K c ) were estimated from the shaded area (SA) beneath grapevine canopies at solar noon in vineyards with different trellises and row spacings. The trellises included the vertical shoot positioning (VSP) trellis, Lyre trellis, single and double curtains, cross-arms of varying lengths, and sprawl systems (shoots not positioned). Measurements were taken throughout the grape growing regions of California. The percent shaded area (PSA) was multiplied by 0.017, slope of the relationship between PSA and K c , to calculate the K c . Vines used to measure SA were not stressed for water as midday leaf water potential was ≥ −1.0 MPa. The seasonal increase in SA was significantly correlated with the accumulation of degree-days (DDs; base 10°C from the approximate date of budbreak) across locations and years. The PSA was a significant function of trellis – wider trellises spread the canopy and increased SA more than narrower trellises, thus having greater K c values. The mid-season K c (K c mid ) for the Lyre and VSP trellises on a 2.74 m row spacing were 0.96 and 0.49, respectively. In addition, K c mid was inversely correlated with vineyard row spacing – the closer the row spacing for a particular trellis, the greater the K c mid . The K c mid for a VSP trellis on 1.83 and 3.05 m row spacings were 0.87 and 0.52, respectively. In contrast, the effects of vineyard row direction and location were minor. The seasonal K c values developed here do not decrease from mid-season, even after harvest, with a few exceptions. Equations given herein express the seasonal K c as a function of degree-days, trellis type, and row spacing, thus providing useful estimates of seasonal K c values for use in California or elsewhere in vineyards with trellises like those in this study. • Vineyard crop coefficients were developed by measuring the shade beneath the canopy. • The K c values were predominantly a function of trellis and row spacing. • The values of K c could be derived from degree-day accumulation across locations. • The K c values would provide ET c estimates to objectively deficit irrigate.