Vineyard Irrigation Scheduling

Kc peaks at 0.7 during bloom/canopy development because that's when the vine is putting on its most leaf area and drawing the most water relative to reference evapotranspiration — a young, small canopy at budbreak (Kc 0.3) simply can't transpire as much water as a fully leafed-out vine, and the canopy's demand tapers again toward veraison and harvest as growth slows and deficit irrigation is intentionally applied. These Kc values follow the FAO-56 crop-coefficient framework (FAO Irrigation and Drainage Paper No. 56, Allen et al., 1998), the internationally standard method for translating reference evapotranspiration into a specific crop's actual water use at a given growth stage.

Regulated deficit irrigation is a deliberate viticultural technique, not an oversight — reducing water at harvest/post-harvest concentrates sugars and flavor compounds in the remaining berries and helps control excessive vine vigor. The calculator applies each stage's own deficit multiplier (as low as 0.4 at harvest) to the full-replacement gallons figure to produce a "Deficit Irrigation Target" output that reflects this intentional underwatering rather than treating full ET replacement as always the goal.

The calculator assumes vine-spacing-squared as the ground area 'served' by a vine, but the actual leaf canopy doesn't shade that whole footprint — it uses 0.5 for the higher-Kc stages (bloom/canopy development and veraison, Kc ≥ 0.5) where canopy is fuller, and 0.3 for budbreak and harvest where canopy coverage is smaller. This scales the water-use estimate down to reflect how much of the vine's row-and-vine footprint is actually intercepting sunlight and transpiring at that point in the season.

The engine squares the vine spacing value as a simplified stand-in for the true row-spacing-times-vine-spacing footprint, since only one spacing input is collected here. This is a known simplification — real vineyard rows are rarely square-spaced — so the gallons-per-vine figures should be treated as a scheduling starting point, and cross-checked against the Vine Spacing Calculator's actual row-and-vine area if your vineyard uses meaningfully different row and vine spacing.