Drip Irrigation water dispersal studies??

Shullsburg, WI(Zone 5a)

Drip irrigation looks impressive on the surface (figuratively!). However after studying root growth of common vegetables, it appears that each plant is going to need a lot of "drippers" during full growth. For example, a tomato plant could have roots going out 4 feet in just one direction. In good drainage soil, one dripper would probably only saturate about a one foot diameter area unless it was ran for a long time. This might take 4-5 emmitters per plant! Using emitters with a greater flow rate would increase this rate but would not provide even watering. There are some drip type hoses (not soakers though) that could simplify things a bit and keep the cost down! But this could take several years of experimentation to get it right on an individual basis. Varying soil composition and mixed planting only compounds the problems.

Some general studies showing saturation rate for various soil compositions and with different emitter rates would provide the necessary technical information to make a more appropriate initial installation.

Does anyone know of such studies or have any knowledge along this line?

Thanks

Lewisville, MN(Zone 4a)

I use my own experience, 25 years worth.
Go online & Google T-Tape. A wealth of information on there. T-Tape is the lowest price & easiest to use.
We use the 8" spacing for our vegetables. Near drought summer 2012. We had great crop irrigating with the T-Tape.

We grew radishes nearly all summer because we could keep them wet.
Pickles were picked 3X a week even in the hot & dry summer. Big yield too.
There the tape is under green plastic mulch. Rows were 265 ft long. We watered 3 rows at a time. About 3 hours, every other day.

These pictures show some of the components & tomatoes in a high tunnel.

Thumbnail by CountryGardens Thumbnail by CountryGardens Thumbnail by CountryGardens Thumbnail by CountryGardens Thumbnail by CountryGardens
Lewisville, MN(Zone 4a)

These are strawberries with T-Tape watering.
We picked these 3X a week from May 26 until frost in October.

Thumbnail by CountryGardens Thumbnail by CountryGardens Thumbnail by CountryGardens Thumbnail by CountryGardens
Lewisville, MN(Zone 4a)

These are pictures of the pickles.
First is July 10. Second is August 5.

Thumbnail by CountryGardens Thumbnail by CountryGardens
Everett, WA(Zone 8a)

When the em itters are spaced 8" aparft, do you also run a T-tape every 8"?

Or is it just one T-tape per row of plants?

>> Rows were 265 ft long

Wow! The relatively cheapo 1/4" dripline I bought advised no more than a 50 foot run, but that was 1/4" and n on-preessure-compensating emitters.

Thanks for sharing your experience!


Contra Costa County, CA(Zone 9b)

I am more familiar with the Tech Line products, by Netafim.

However, there are soil saturation patterns based on the soil type.

Here is info from my Soils textbook, mumbly... mumbly years ago:
The course was more geared toward agriculture, not home gardening, and the soil is not amended with compost or much else. Just good 'ol dirt.

Dig a shallow hole, then fill it with water. Let the water soak in, then dig deeper into the hole to see how deep the water went. If your hole is 1' x 1' and you put 1" of water in it that is .6 of a gallon, just over half a gallon.

Soil type............Inches of water to soak in 1' deep
Sand----------------.5-.7" = 1/2" of water or 1/4 gallon on top soaks in a foot deep in pure sand
Loam--------------1.0-1.8" = between .6 gal to 1 gallon to soak a foot deep in loam.
Clay---------------1.4-2.4" = As much as 1.5 gallons of water to soak in a foot deep in clay soil.

Max rate to apply water based on soil type (bare soil- no mulch) for minimum puddling:
Sand--------------.75" per hour = a bit under 1/2 gallon per hour
Loam--------------.35" per hour = about 1/3 gallon per hour
Clay----------------.15" per hour = a bit less than 1/10 gallon per hour

My note: The high compost levels in many of the vegetable gardens we are talking about can take in water a lot faster than that. You can apply the water a lot faster in these amended soils.
The faster the water is applied the wider it spreads on the surface, and the less deep it goes. This is fine for shallow rooted plants like most of the small vegetables. You can get the same effect with closer spacing of the holes in the tubing.

When I set up Tech Line for a client's raised vegetable beds the tubing can be as much as 2' apart for the larger plants, and I usually use .95 gallons per hour @ 12" spacing. Pretty much the whole bed gets wet on the surface when it is run for a couple of hours.

When I used drip many years ago, (and had really bad water) I used tubing with holes 12" apart, and spaced the tubing 12" apart. The flow was set at 20 gph. The lines were (mostly) 16' long. This would apply 1.25 gallons per square foot per hour. I ran the water until it puddled, which took a while. I had a lot of compost in those beds. I do not use drip now, even though I have better water.

As for the actual wetting pattern... At the surface you will see just a small spot where the water is entering the soil. Under the soil the water is wicked sideways depending on soil type. The shape is sort of like an ellipse. If you apply water at the slow rate listed above to:
Sand.... the water will go pretty much straight down. Minimal spread. Couple of inches wide.
Loam... the water will spread out several inches wide as it gets deeper into the soil.
Clay...... the water will spread quite a bit under the surface.

Lewisville, MN(Zone 4a)

One T-Tape per row. 8" spacing wets the entire row. It's all built into the tape. On large acreage runs are way longer than ours. Really are unlimited. They only need 4 lbs of pressure. At one time we had some acreage with no water supply. We just hooked up to a 750 gallon barrel on a wagon. Gravity did the rest.

Everett, WA(Zone 8a)

Dianna_K said:
>>>>>>>>>>>>>
Max rate to apply water based on soil type (bare soil- no mulch) for minimum puddling:
Sand--------------.75" per hour = a bit under 1/2 gallon per hour
Loam--------------.35" per hour = about 1/3 gallon per hour
Clay----------------.15" per hour = a bit less than 1/10 gallon per hour

Everett, WA(Zone 8a)

Country Gardens said:
>> They only need 4 lbs of pressure.

That explains why one guy "blow apart" some Tee tape. I think he wasn't regulating the pressure and might have had 45 PSI.

>> Really are unlimited.

I guess 1/4" dripline like mine is why short runs were advised. I guess pros use 1/2" dripline or the tape. I wonder what the effective bore of the tape is?

Contra Costa County, CA(Zone 9b)

You might check with each manufacturers' web site to see how long a run will work, and at what pressure.
Obviously tubing with more holes or larger flow rates will simply run out of water sooner, but a slow drip rate might make some really long runs possible. Especially with larger tubing.
Smaller diameter tubing will have more turbulence inside, making it less efficient for moving larger amounts of water, which is why the main line should be larger, then reduce down at each plant or each close group of plants.

The site that I looked at (Netafim, makers of Tech line) have charts that show spacing of the tubing in different soils, flow rates and lot of other info.
As a partial answer to what the wetting pattern looks like in different soils you can see the recommended spacing, and run times for something as demanding as turf. This would evenly wet the soil under the lawn, so that is how far sideways the water moves in different soils.

http://www.netafimusa.com/files/literature/landscape/dripperline/LTLCVDG-Techline-CV-Design-Guide.pdf

Everett, WA(Zone 8a)

>> a slow drip rate might make some really long runs possible. Especially with larger tubing.

Yup. With any tubing, even with no water outlets, there is a specific drop in pressure per foot at any specific flow rate in feet per minute. When that's smooth, laminar flow, the drop is very small. But as soon as you get into turbulent flow, the pressure drop per foot is much higher.

I think that is why vendors toss out unqualified numbers like "1/4 inch tubing can "handle" 40 GPM.
or 1/2" tubing can handle 240 GPH = 4 GPM
or 3/4" tubing can handle 480 GPH = 8 GPM

They are probably quoting a flow rate (in GPM) that requires a flow rate (in feet per minute) that almost causes turbulent flow. In other words, if 4 GPM caused a 5 PSI pressure drop per 100 feet due to laminar flow, 4.5 GPM might cause a 20 PSI drop due to turbulent flow.
One once turbulent flow takes over, 4.75 GPM might cause a 20 PSI drop in just 10-20 feet.

But as soon as you add barb fittings, there are constructions that cause localized turbulence at each fitting. I wonder whether the "40 GPH" quote for 1/4" tubing with 0.170" ID assumes that you also have two barbs in it, each with an ID around 0.140" (I guess).

Lewisville, MN(Zone 4a)

That's the part of T - Tape. The entire tube fills before drip starts. On their web site they list 975 ft as the longest run.
We do 3 at 265 ft, which is getting close.

We "blow" one every now & then. We have a supply of splicing connectors on hand. Be sure & retrieve them at the end of the season.

We use the 6 mil size. 5/8" diameter. It comes in a 10,000 ft roll for $200.00. We have to buy new each year because we lay it with a machine. In the picture.

One year we were going to save money & bought 4 mil. It blew apart very easy. Was a mess actually.

Thumbnail by CountryGardens
Everett, WA(Zone 8a)

I added that to my notes!

100 feet for $2.00? 2 per foot??

Good deal! I looked at John Deere and DripWorks T-tape.

5/8" diameter = 0.625" (Is that ID or OD? At 6 mil, maybe the ID is 0.613" ?

Either way, it ought to support a little more max flow than "1/2" mainline", say 300-350 GPH, which I would have though was ~350 emitters at 1 GPH, or 700 at 1/2 GPH.
700 emitters at 8" would be around 1,000 feet.

Anyway, my application is the very opposite of long rows: my very longest series of adjacent beds would be around 60 feet.

I see that "1/2 inch mainline" has 50 mil wall thickness, so I see why T-tape has a recommended pressure of 8 PSI, and a max PSI rating that depends on wall thickness (i.e., price).

I guess slope is big deal with T-tape, since a 10-foot drop would increase pressure by 23 PSI.

Post a Reply to this Thread

Please or register to post.

Upload Images to your reply

    You may upload up to 5 images
    BACK TO TOP