No Irrigating Or Weeding For 10 Years

That’s the promise of this simple new dryland production system –
a combination of polymers in the soil bed and a polypropylene mulch over the top.

By Daniel J. Wofford Jr. and Michael D. Orzolek

Growing vegetables in dryland areas – those that receive 8 to 25 inches of rainfall annually – traditionally has been a labor- and input-intensive business. But an innovative new type of vegetable growing system has demonstrated it may be possible to construct dryland beds that don’t need to be irrigated, weeded, or cultivated for up to 10 years.

The system – called the Hydrosource/DeWitt Sunbelt Dryland Water-Catchment System – was first developed in Colorado and is currently being tested in 12 states and four foreign countries. One bed was also constructed at Pennsylvania State University, with indications that the system may have some significant advantages – especially in weed control and elimination of occasional irrigation – at higher rainfall sites as well.

Basically, the system involves a three-step process: incorporating polymers into the soil; covering the bed with a polypropylene moisture/weed/erosion barrier that allows rainfall penetration but severely retards both weeds and evaporation; then either planting or transplanting vegetables through 3-inch slits made with a propane torch into the trampoline-like bed.

In a recent test in Hugo, CO (see sidebar), vegetables thrived on as little as 2 inches of rain over a 75-day period.

Holding Water

Key to the system is incorporation of moderate to high rates of cross-linked polyacrylamide (CLP) polymers (in this case, Hydrosource) in the beds to a depth of 5 to 10 inches. (Polymers are long-lasting, gel-forming, water-absorbing materials that can absorb more than 400 times their weight in distilled or pure water. See American Vegetable Grower, February 1992, page 22.)

But good bed construction at the outset is crucial to the success of the system for several reasons: It prevents wind damage, reduces evaporation, and stops weed growth. The most important step is to tie down the outside borders of the polypropylene barrier – we used DeWitt Sunbelt – with fabric pins, railroad ties, used carpet, or even dirt to prevent wind damage.

How well does the CLP work? At the rate of 100 pounds of polymer per 1000 square feet in the Hugo test. it was possible to capture and store more than 5 inches of additional rainfall, apparently for months at a time, with minimal soil moisture loss from under the DeWitt Sunbelt. (Polyethylene mulch has been tried in conjunction with the polymers, but has not been successful because the plastic is impervious to water and may also affect gas exchange in the soil.)

It’s not completely known how much of this water retention is due to the polymers and how much is due to the barrier. Research at a USDA-ARS test station near Cheyenne, WY, found that available soil moisture under Sunbelt – without the polymers – did not fall below 85% during the hottest and driest part of Wyoming’s summer. However, without the polypropylene cover, nearby fallow ground dropped to 3% available soil moisture.

Controlling Weeds

The system has also demonstrated good weed control, thanks solely to the Sunbelt barrier. Colorado bed owners report an average of 0 to 12 weeds per 1000 square feet per growing season, with the number of weeds generally varying with the size of the planting slits. The tightly woven, black fabric blocks out most of the light needed for optimum plant growth under the material – but we understand that some sharp-bladed grasses in other parts of the country will occasionally penetrate the Sunbelt.

One disadvantage of the barrier is that some scalding of plants or fruit does occur during the hotter parts of summer when tomatoes rest directly against the black fabric. Also, while spring transplants do fine, mid-summer transplants appear to suffer some from heat radiated off the black Sunbelt.

Little is known of the effects of both absorbed and radiated heat off this black polypropylene fabric, but mulching with bark or a future color change in DeWitt Sunbelt could be made to counter the scalding problem on affected plants such as tomatoes and strawberries. An upcoming test of Sunbelt spray painted with white and lighter colors should allow this problem to be evaluated.

There is one added benefit to the system: The combination of CLP and the barrier may significantly increase crop yields and bring about earlier maturity compared to conventional growing.

Why? Obviously the actual water storage impact is part of the benefit, but – based on observations alone – stress reduction appears to be more important. Soil microorganism activity may also be much higher in beds with high polymer rates – especially when evaporation is held to a minimum by using a fabric barrier.

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2 Inches Of Rain in 75 Days

Probably the most interesting dryland vegetable bed was installed by Renee Hink, a Colorado State University extension agent, at a 14-inch annual rainfall site at Hugo, CO. The site was planted 2 weeks late on May 20, 1993 and the bed was watered in at planting time to simulate some holdover storage of snowmelt and early spring rains.

For the next 75 days, a National Weather Service Station 15 miles away recorded only 2.14 inches of rain – yet Hink’s garden continued to flourish without irrigation (Semi-Arid “No-Irrigate//No-Weed” Gardening in Eastern Colorado – 1 August 1993). The dryland system’s ability to retain up to 5 inches of water indicates it may work at much lower rainfall sites than originally calculated – probably because the Sunbelt barrier’s capability to prevent evaporation was underestimated.

In fact, the system has been successfully tested at a number of sites across the country.

For more information on the Hydrosource/DeWitt Sunbelt System, contact: Western Polyacrylamide Inc., Daniel J. Wofford, Jr., Click Here For Contact Information

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Long-Term Cost-Effectiveness

As for the lifetime of the system: There are some good indications that the Hydrosource/DeWitt Sunbelt System will last 8 to 10 years. The sodium-based Hydrosource CLP was selected because of its proven, almost 7-year survival record to date in Colorado, plus the fact that the hydrated granules will survive hundreds of freeze/thaw cycles without obvious damage.

Further, the woven, porous Sunbelt contains an effective ultraviolet (UV) blocker for longer life. It carries a 5-year guarantee, but it already has a documented record of almost 9 years of performance on Colorado windbreak and “Living Snow Fence” sites. The current condition of Sunbelt installed in 1985 at a Colorado site indicates it should last at least 10 years.

Since UV damage increases at roughly 4% per 1000 feet of elevation, and most of the Colorado tests fall in the 5000- to 8000-foot elevation range, growing regions in other parts of the country would show an even longer lifetime.

The long life of the system is an important factor, because initial installation costs are somewhat high. Total cost is difficult to estimate at this stage, since optimum rates for different soil types and different environments have not yet totally been determined. Wholesale (full roll) prices for the Sunbelt barrier run in the 5¢- to 7¢-per-square-foot range, while the bulk price of Hydrosource cross-linked polyacrylamide (in 50-pound bags) is around $3 per pound.

However, performance of Sunbelt-only beds at several sites indicate we can probably use much less CLP. Most current systems have been designed for 100% dryland production in semi-arid Colorado by using 100 pounds of polymers per 1000 square feet to capture and store the 5-plus inches of rainfall needed to withstand prolonged droughts. Some users with irrigation options have already started using polymers in the 10- to 25-pound range and simply water occasionally during droughts.

Gaining In Popularity

Four Hydrosource/DeWitt Sunbelt beds were constructed in Colorado in 1992, followed by 30 worldwide in 1993 and several hundred scheduled for the 1994 season. This increased production should provide a much clearer picture of the future of this emerging technology.

Part of the fascination with this intriguing system lies in its utter simplicity, and the fact that anyone with Hydrosource CLP, the DeWitt Sunbelt, fabric pins, and some ingenuity can design and construct his or her own tests.

Wofford is president, Western Polyacrylamide Inc., and Orzolek is professor, vegetable crops, Department of Horticulture, Pennsylvania State University, University Park, PA.

Western Polyacrylamide, Inc.
Daniel J. Wofford, Jr.
Click Here For Current Contact Information

American Vegetable Grower • November 1993