Irrigation Amount and Frequency

Irrigation Amount: how many hours of water
Determines water consumed in acre-inches and calculates water to apply. Sum the hours irrigated and calculate a week or two of ETc in spreadsheet to figure out how much to irrigate this week. Will need to examine soil moisture data and pressure bomb data to learn the drying cycle of your vineyard. Use this method from start through veraison, and modify Km post-veraison.

    Ia = water applied or irrigation to apply. Ia = (ETo * Kc) * Km
    ETo = water use if a grass, depends on weather
    ETc = water use if grape, depends on weather and vine, ETc = ETo * Kc
    Kc = grape crop coefficient (between 0 to 1). Be consistent in what Kc you use.
    Km = management coefficient, changed according to field observations or from pre and post veraison, if 80% of ET then = 0.80

Irrigation Frequency: How often and duration
Maximum duration = the water holding capacity of weakest or shallowest soils in the block. (reference values in Ref #2). Pick two times a week, then monitor mid-day water potentials with pressure bomb at weak and strong parts of a block after irrigating and if stressed, increase frequency by one or two days and decrease the amount per application so Ia stays the same.

Common mistakes:
Not irrigating under cool weather. In fact water use is more dependent on humidity, sunlight and wind than temperature. Irrigation is not efficient or uniform.

Further reading:
1. CM Burt and SW Styles. 1999. Drip and Micro Irrigation for Trees, Vines, and Row Crops. ITRC, Cal POly San Luis Obispo, CA.
2. Irrigation Scheduling: A Guide for Efficient On-Farm Water Management. DA Goldhamer and RL Snyder, Eds. 1989. University of California publication 21454.
3. Micro-irrigation of Trees and Vines. L. Schwankl, B. Hanson, and T. Prichard. Eds. 1996. University of California publication 93-03.
6. Willams, LE 2001. “Irrigation of Winegrapes in California” Practical Winery and Vineyard. pp. 42-45
Greenspan, Mark. “Vineyard Water Management Fallacies”, Wine Business Monthly (pdf)
Open questions that require more literature to review:
Is this done on a per block basis? Seems like a lot of labor. how can this be automated? How soon to measure after irrigating to know if block is too stressed?

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