The ABC’s of Starting with Drip Irrigation

by Keith Baldwin, CFSA’s Farm Services Coordinator

With Spring approaching, it’s time to think about that new drip irrigation system for next year. What’s it going to cost and how much water will you need to run it? Let’s look at a vegetable crop situation. “Standard” drip tape (such as T-tape or AquaTraxx) for vegetable crops comes in 7,500 foot rolls. One roll costs about $165. Most vegetable producers would buy 8 ml tape with an emitter spacing of 12 inches. The specs for this standard tape state that it emits 0.45 gallons of water a minute (at 10-12 psi). The table below indicates that the amount of drip tape that would be required at different bed spacing (center to center) and the amount of water “capacity” that you would need to run the system.

If you’re irrigating from a well, it needs to yield and deliver these amounts to run the system for an acre of vegetables. If you have different emitter spacing, you would need to adjust for that. Not enough water? Drip tape is available that only requires half of the volumes described in the table above. But that doubles the time that you would need to run the system to meet crop water needs.

How much water do vegetables need? As a general rule, vegetable plants at canopy closure use about an acre-inch of water per week in the Carolinas; that is, one acre uses one acre-inch or 27,156 gallons of water a week (3,880 gallons per day). If you’re using drip tape on beds with six foot centers that delivers 33 gpm, the irrigation run time is about two hours. Sandier soils should probably have that irrigation run time split into two one-hour sessions.

Other components of the system that you would need include:

• Polyethylene “header” pipe (3/4 inch is fine for quarter acre irrigation blocks) costs about 20 cents a foot;
•  Fittings to connect the drip tape to the poly are currently priced anywhere from $0.50 to $1.50 each (the latter having individual on/off valves);
• A filter/pressure reducer varies in cost, but figure $40;
• Anti-siphon valves prevent backflow into your well and cost $8 to $15.

Considering Plastic Mulch?  Read this First

There is a good deal of discussion among the organic community about the use of plastic mulches. The good news is that manufacturers continue to work on biodegradable mulches. There is currently a product available called Bio360 biodegradable plastic mulch film (0.6 ml) that is made from non-genetically modified corn starch. The company claims that it completely biodegrades in the field. However, it’s not currently certified by OMRI, and organic producers should treat it as a “prohibited” until more information is available from certifiers. It’s currently priced at about $265 for a 48” X 4000’ roll. If you are using standard plastic mulch, you’ll pay about $150 for standard 1 ml, white on black mulch (48” X 4000’) and $121 per roll for 1 ml black mulch.

A Special Case: Blueberries and Brambles

How about irrigating blueberries and brambles? Two 0.5 gallon per hour (gph) emitters in 0.5 inch polyethylene tubing at each blueberry plant are sufficient when plants are small, and additional emitters can be added as plants grow. There are 218 plants on a quarter acre if bushes are spaced five feet apart in the row. To water the entire quarter acre would take 218 gph or 3.6 gallons per minute (gpm). A 0.25 acre blueberry planting on 10 foot row spacing would have an irrigation run time of 6.6 hours/week in mid-summer for bearing plants.

For blackberries, polyethylene tubing with inline one gph emitters (12 inches apart) can be used. Likewise, a quarter acre of blackberries planted on a 10 foot row spacing with one gph inline emitters spaced 12 inches apart would take 1090 gallons per hour or a little over 18 gallons per minute. Weekly run time to supply that water through the inline system is 2.8 hours.

The weekly run times should be “split” into daily applications, depending on the weather. Daily applications can be split if small fruit is on sandy, well-drained soil.

CFSA can help with your questions! Reach out!

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