Evapotranspiration and Irrigation---Part 2

The heat wave continues. We have a smallish garden on our land but until this year no water source other than hauling water in a 40 gallon plastic container. Now that my husband has constructed a 275 gallon water tank using an IBC (intermediate bulk container) that he purchased used, I am watering our garden with abandon! I think that my previous problems with leathering of my tomato leaves had everything to do with my watering schedule (or lack thereof).
What does this have to do with grapevines, you ask. With the heat wave continuining, irrigating the vineyard may become necessary. The proper timing and amount of irrigation is critical in the production of quality grapes. The following information has been summarized from an excellent article called Irrigation Scheduling of Grapevines with Evapotranspiration Data written by Ed Hellman, Viticulture Extension Specialist.¹

Determining When to Irrigate:
• Know soil characteristics to understand moisture holding capacity
• Cover crops can impact vineyard moisture depletion
• Monitor grapevine water status

Determining How Much Water to Apply
• Use the Water Requirement Formula to calculate how much water is needed: [ETo X Kc] divided by the irrigation system efficiency
• Get the reference evapotranspiration date (ETo) for your area
• The crop coefficient (Kc) can be estimated
• The system efficiency is:
  • Drip irrigation between 0.85 to 0.95 (i.e., 85-95% efficient)
  • Sprinkler irrigation between 0.60 to 0.75
  • Furrow irrigation between 0.40 - 0.50

The article Irrigation Scheduling of Grapevines with Evapotranspiration Data, which is 6 pages in length is a concise explanation of how to calculate the water requirements of your vineyard including an example calculation.
In addition, evapotranspiration information can be obtained from both the Texas and California sites. Unfortunately, for us in the Northeast, I haven't come across a similar ET site:
Link to the TexasET Network
Link to the California Irrigation Management Information System (CIMIS)
Another article that can be found online is: Irrigation of Winegrapes in California, Larry E. Williams, Practical Winery & Vineyard Journal, November/December 2001.

1. Irrigation Scheduling of Grapevines with Evapotranspiration Data, Ed Hellman, AgriLIFE Extension, Texas A&M System.