Thursday, May 20, 2010

Drip Increases Yields, much of the time

Numero uno is one of the often poorly-understood concepts about drip irrigation.

There are many scientific studies which indicate that drip irrigation can improve growth and yields. For example, in 1981 T. A. Howell et al surveyed 50 research reports on crops grown with drip irrigation, and concluded: “Where trickle [drip] irrigation was compared with either no irrigation or other water-application methods, yields were equal or better in all cases; and the amounts of water applied were equal or less with only two exceptions.” (As summarized by D. A. Bucks and F. S. Nakayama and A. W. Warrick in “Principles, Practices, and Potentialities of Trickle (Drip) Irrigation,” Advances in Irrigation, Vol. 1).

Research in many different climates and states invariably supports the benefits and cost-effectiveness of drip irrigation. Art Gaus, an extension horticulture specialist with the University of Missouri at Columbia, MO, has had a drip system in his personal garden for nine years. One summer, his bush watermelons with plastic mulch and a drip system produced 32 pounds in a four-by-four-foot area, compared with 9–16 pounds in the same area with conventional irrigation. He reckoned a well-timed drip system “could mean a 100% increase in yields; during the droughts of 1980, ’83, and ’84, it meant the difference between having a crop or no crop at all.”

In a study of established pecan trees in Georgia, trees with drip irrigation added had a 51% increase in yields.

Michigan State University has documented a 30% yield increase in vegetable crops with drip irrigation, even in its humid, summer-rain climate.

A study in India in 2002, found that with chilies, water use was down 34–50%, while production was up 33–48%. The researchers attributed this to irrigation that kept the soil moist, not too dry.

A study in New Mexico found amazing differences in yields compared to [respectively] furrow and drip irrigation: 18 pounds versus 30 pounds with cucumbers, 69 to 156 pounds growing Swiss chard, and 64 versus 166 pounds with green beans—to quote a bit of the study. [It is interesting to note that broccoli, Brussels sprouts, and carrots didn’t have any greater yields in the drip irrigation plots. Yet, a study at Oregon State University found a 20% increase in carrots compared to plots with sprinklers.]

To be fair, the benefits of drip irrigation are not confirmed across the board in agricultural studies. There are a number of studies which show it to be less beneficial than sprinklers, especially with perennial and tree crops. One such example is found in a paper entitled “Growth and Yield of Rabbiteye Blueberry as Affected by Orchard Floor Management Practices and Irrigation Geometry,” by K. D. Patten et al. in The Society, September 1989, Journal of the American Society for Horticultural Science, Vol. 114 (5) pg. 724-728. This study found that 360-degree sprinklers created better plant establishment and growth than either one emitter or two emitters per shrub. This is one of many cases where agricultural limitations (such as having to keep the area between tree rows free of tubing and emitters so tractors can mow or disc) greatly restrict both the number of emitters which can be used and their placement. In my drip-irrigation book (Drip Irrigation for Every Landscape and All Climates, 2nd Edition, Metamorphic Press, 2009), I very specifically recommend that emitters be placed equidistant throughout the entire root zone—which would include the area equivalent to that between the rows. The results in the abovementioned study are only to be expected when a dramatically reduced proportion of the root zone is watered by a mere emitter or two.


Let me know what you think. Visit my web site ( to learn about my new book on drip irrigation and other gardening books. Thanks, Robert

Lawn Irrigation That's Really "Out of Sight"

Lawns, yawns. They aren’t needed as much as they are found. However, there's no better place to have young kids run around and, play badminton or croquet, or necking while watching the stars. (This subsurface approach to irrigation means you can neck at the same time the lawn is being irrigated!)

The latest revolution in irrigation is happening quietly underground, four to eight inches beneath lush, but water-conserving lawns. Although landscape professionals have long utilized the water-conserving efficiency of drip irrigation for most other types of plantings; combining it with lawns has, until recently, been an unsolvable problem.

Now, however, it's possible to irrigate lawns with emitters buried safely beneath the soil's surface that save even more than the 20-50% watering efficiency of surface emitters.

The idea of subsurface lawn irrigation often raises many concerns. What, for instance, keeps the entombed emitter from becoming plugged by soil? The answer is in-line emitter tubing. The emitters, which are located inside this tubing, contain a lengthy internal pathway which is known as a complex, turbulent or tortuous path. (See the illustration here from Drip Irrigation for Every Landscape & All Climates.) When the system comes on, water pressure purges any soil that may have entered the emitter's orifice. The turbulent pathway is also very self-cleaning when sediment is suspended in the water.

Another common concern is the possibility of the emitters becoming clogged with grass roots. This can be prevented by timed irrigations, which should be both frequent (daily or even hourly) and very brief. Depending upon the soil and climate, for only a matter of minutes, or less—depending on the number of start times. Some brands of in-line tubing also come impregnated with a pre-emergent herbicide which kills root growth at emitter openings. (The roll photographed here has the noticeable greenish tube emitters.) While no organic gardener would use the Treflan™ found in the impregnated emitter, it’s toxicity is very low and the chemical does not migrate far from the emitter.

Designers and clients also may worry about unevenly-watered lawns with telltale green-brown-green striping. Mark Dargay, of EH Griffith Inc., (a distributor of TechLine™ in-line tubing) designed the subsurface irrigation for the Market Square project, 12,000 square feet of turf and trees in downtown Pittsburgh, PA. "I was very leery," Dargay remembers, "I envisioned striping of the lawns." After two summers of healthy non-striped growth, he’s "very pleased."

A word of caution: neophytes in drip irrigation should make their first mistakes above ground with visible or mulched in-line tubing before attempting a subterranean "deployment."

Dennis Hansen, a L.A. and Certified Irrigation Designer in Fairfield, CA, advises designers new to subsurface irrigation to "start with no more than 1000 square feet. Or, hire an irrigation designer with enough experience to have a defensible and insurable status."

The details of how to design an efficient system can be found in my book— Drip Irrigation for Every Landscape & All Climates.

P.S. DON’T attempt if you have gophers. Best in urban areas.


Let me know what you think. Visit my web site to learn about my new book on drip irrigation and other gardening books. Thanks, Robert

Drip Paraphernalia

It' time for tuning up & testing drip systems. If, gawd forbid, you have a a system with lots of punched-in emitters you'll need to carry around spare emitters, a punch, goof plugs & more. Use a box with lots of chambers like the sewing paraphernalia shown on the left. Or, boxes used for fishing hooks & gear or small tool boxes with transparent plastic covers. Although the sewing box is illustrated in my book, Drip Irrigation for Every Landscape & All Climates, you can skip most of these tiny, tedious parts by using in-line tubing where there are no emitters to break off, adjust, or repair. The in-line tubing in this patch of beans (on the right) is streamlined, easy to roll out, and you can never damage the internal emitter. With a two- to four-inch mulch layer over the tubing, you can walk or use a wheelbarrow on top of the tubing with no damage. Light folks can even step on the tubing without damage. Be sure to flush all lines before starting to use the system.


Let me know what you think. Visit my web site to learn about my new book on drip irrigation and other gardening books. Thanks, Robert

Sunday, May 16, 2010

Basket Bondage?

It’s spring in full-tilt boogie. Where there are gophers, the trend has been to plant in wire baskets. In the past ½-inch aviary wire was used. While fairly easy to work with, it doesn’t last a long hardware cloth with regards to rust. There are some pre-made commercial wire baskets. They aren’t very deep, but the wire is studier than aviary wire.

The fear is what happens to the roots that grow thru the wire. As illustrated in my blog of 5/10/10, many roots are eaten at the wire’s edges. This makes the plant more like a container plant with the roots feeding only within the wire basket. Those that do manage to escape the cruddy teeth of the western pocket gopher have to deal with growing in and thru the wire.

The question is as the roots that grow thru the basket, as shown on the left, get harmed and is growth reduced? Wire can be included within the tissues of growing plants without apparent harm. The other photograph shows how an oak tree is slowly swallowing a 4” X 4” sign post.

In my experience a plum tree planted in a very shallow wire basket was greatly stunted. It failed to produce the thicket of long spindly shoots each summer. With all the other trees planted within 4’ deep & 3’ wide baskets, seems the trees a perfectly happy. They are the Asian pear, plum, plumcot, apple, and persimmon trees.

So it seems wire is simple swallowed up by the basket and the transport of water & nutrients up-and-down the tree remains relatively unharmed.


Let me know what you think. Visit my web site to learn about my new book on drip irrigation and other gardening books. Thanks, Robert