High tunnels extend season, protect crops, eVGN September 2013
“High tunnels extend the growing season two to four weeks,” said Schultheis, a natural resource engineering specialist with University of Missouri Extension. “Farmers can make supplemental income on small acreages, without having huge capital expenditures, and can provide consumers with high-quality, locally grown produce.”
Schultheis gave a presentation on “Drip Irrigation Considerations in High Tunnel Production Systems” during a recent workshop in Camdenton, Mo. He urged growers to visit other sites where high tunnels have been located and ask questions regarding those operations before embarking on their own projects.
“Be prepared for the unexpected,” Schultheis said.
The advantages of high tunnel production systems/drip irrigation use in vegetable growing include the likelihood that crops would be less prone to fungal diseases because the plants remain drier.
Schultheis said nighttime temperatures indoors can average 4˚ F higher than outdoors. High tunnel use increases production and marketing opportunities while offering shelter from wind, hail and insects – reducing disease pressure. The system enables the grower to control the water supply, and many of them are designed as “drive through” for the use of field equipment.
Site selection and location for high tunnels is critical. The best spot is on a flat site on suitable soils, or soils that can be easily amended. For a stationary unit, plan to amend the soil each season or year to maintain fertility. Orient the structure perpendicular to the prevailing winds on the farm. All of the ventilation is manual, so there will be a dependence on the wind to ventilate. The end wall should be faced toward the winter wind.
Not selecting the side curtains (roll up vs. roll-down) based on the type of crops to be grown is a common mistake, Schultheis said.
“Crops do best if they don’t have cold drafts on them,” he reported. “Lack of attention to ventilation and not monitoring soil moisture regularly are two big concerns.
“And the structures are more prone to weather damage from high winds, snow and ice,” Schultheis said.
He said high humidity early in the growing season can lead to increased disease problems.
Drip irrigation from a high-quality water source is mandatory to supply the crops with nourishment, since everything is undercover. With a high tunnel there is a need to water crops, even when it rains. Producers need to regularly monitor for temperature, humidity, disease and ice.
Checking soil drainage conditions is essential. Available water-holding capacity depends on soil texture, organic matter and rooting depth.
“If you take care of your soil, the soil will take care of your plants,” Schultheis said.
He mentioned soil texture classes: sand, which adds porosity; silt, which gives body to the soil; and clay, which provides chemical and physical properties.
He said there are benefits to adding compost to the high tunnel environment, including improved drainage and aeration of heavy clay soils, increased moisture-holding ability of sandy soils, enhancing earthworm and soil microbial activity, better soil structure and providing nutrients needed for plant growth.
Using drip irrigation – also known as trickle, micro and low-volume irrigation – in high tunnels provides for a low rate and uniform water application and improved disease and weed control, in addition to allowing the field to be worked during irrigation. It also works well with plastic mulches.
The downside of drip irrigation use would include a lack of frost protection. Also, emitters – while allowing for a variety of spacing and separate crop irrigation strategies – can plug easily from too much iron, calcium, sand, algae and some fertilizers entering the system. Tube and drip tape damage from rodents or even a hoe can occur.
Schultheis offered extensive details regarding drip irrigation system structure, installation and operational methods, as well as specific soil and irrigation requirements for selected vegetable crops in high tunnel operations.