Page 60 - Summer 2019 Journal

Because you can grow so much more in a high tunnel, and grow it much more quickly, the soils in high tunnels get far more of a workout than outdoor soils.
technology. From irrigation to ventilation, high tunnels are now benefiting from much-needed automation. Low-cost sensors can track ev- erything from soil moisture to air temperature and humidity, and it is possible to partially or fully automate many different processes. For instance, is the tunnel becoming too hot? Ridge vents will automatically open. Is the soil too dry? The irrigation system will cycle on when the soil sensor sounds the alarm.
When it comes to nutrition, soil tests are crucial for high tunnel growing. No matter what you are growing, a soil test will be the most important thing you can do to ensure proper nu- trient levels and produce healthy, nutrient-dense crops—although such testing is often neglected. Because you can grow so much more in a high tunnel, and grow it much more quickly, the soils in high tunnels get far more of a workout than outdoor soils. Moreover, tunnels don’t get rain, which means that salt build-up and other nutrient issues can set in more quickly. So soil testing is a must.
Tunnels offer unique ways to provide water to plants and soil. Because rain doesn’t fall in a tunnel, farmers usually provide water via irrigation systems. Hand watering is possible but isn’t efficient or recommended. Disadvan- tages of hand watering include the potential for causing sun scald and disease problems on the plants; in addition, hand watering uses far more water than necessary and a great deal is lost to evaporation, which increases humidity in
the tunnel and again can contribute to disease. Fortunately, all sorts of irrigation systems now exist, from drip tape to drip spikes, which not only conserve water and reduce disease but also reduce weeds. This is because these irrigation systems can deliver water directly to the plants and in amounts close to what is needed, giving weeds less access to the water they need to proliferate.
Because you are delivering water anyway, it makes sense to double up and address both water and nutrient needs at the same time. Delivery of nutrients to plants via irrigation water is called “fertigation.” This type of system allows a cus- tom-tailored approach to plant and crop needs, making it possible to apply small amounts of fertilizers and amendments as needed and avoid the problematic application of large amounts at once. Such small applications can help elimi- nate nutrient loss, leaching and groundwater contamination, among other benefits.
Plants also need air. Air plays many roles, such as removing excess heat and moisture, while providing nutrients that plants and soil need. Tunnels that don’t have enough air flow can actually suffer from insufficient carbon dioxide (CO2), along with excessive heat and humidity. Many methods exist that allow you to control and customize the air flow in a tunnel to balance the need to retain heat (especially in the winter) with the need to remove excess humidity and the need for fresh air. First and foremost are drop-down side curtains, along with ridge
TABLE 1. Comparison of greenhouses and high tunnels
GREENHOUSE
HIGH TUNNEL
PERMANENCY
Permanent (20-40 years)
Temporary (10-20 years, with plastic replaced every 3-7 years)
MATERIALS
Glass or polycarbonate panels, sometimes plastic
Usually plastic, some- times polycarbonate
COST
Higher cost
Lower cost
WHERE GROWN
Usually on benches or in containers, some- times in the ground
Usually in the ground or raised beds, sometimes in containers or grow bags
HEATING/COOLING
Active, usually HVAC type systems
Passive*
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*Many high tunnels now also use supplemental heating and cooling systems.
Wise Traditions SUMMER2019