Soil still stable after eight years under high tunnels

A recently published long-term study answers questions about the impact of high tunnels on soil quality. The 8-year study was designed to determine if the presence of a high tunnel affects soil quality in a silt loam soil. Rhonda Janke and colleagues from Kansas State University published their research in HortScience. "In high tunnels, crops and soils are often more intensively managed than field crops," explained Janke. "There were concerns that covering a soil year-round would result in a buildup of insect pests, soil pathogens, and excess nutrient salt levels. However, the decline of soil quality under high tunnels was not confirmed by our research."

The study involved six high tunnels established at the Kansas State University Horticulture Research and Extension Center at Olathe in 2002. The tunnels, constructed with a single layer of polyethylene sheeting over a metal hoop frame, were built on Kennebec silt loam that was formerly pasture. One row of three high tunnels was laid out in a North–South direction with 5.6 meters between tunnels; the second row of three high tunnels was placed 5.6 meters to the East. The six field plots were laid out in the same configuration with plots in a North–South line with the high tunnels, beginning 10 meters to the South of the tunnels. High tunnels and field plots were arranged with alternating organic and conventional management. "This arrangement was chosen to equalize field position so that position would not become a factor in the design of crop experiments," Janke explained.

Vegetable crops such as leafy greens were grown in the cooler part of the year while tomato, eggplant, and other warm season crops were grown in the Summer. Some years, winter cover crops of rye or spring cover crops of buckwheat were planted, but most winters were fallow. Crops were replicated across all plots, and soil amendments were replicated in three high tunnels and three field plots, organic or conventional.

The scientists measured soil pH, salinity, total carbon, and particulate organic matter (POM) in the high tunnels for 8 years. "Soil pH, salinity, and POM were influenced, but not unfavorably, by the presence of high tunnels," the authors wrote. They discovered a significant "location-by-management interaction", finding that soil pH was different between high tunnel and field under conventional management, but was not different under organic management. "It was not simply the absence or presence of a high tunnel that caused a shift in pH," they noted.

"Our results showed that soil quality was not adversely affected by 8 years under stationary high tunnels managed with conventionally or organically produced vegetable crops," the authors said. Although the results showed elevated soil salinity under high tunnels--particularly with organic management--the increase in salinity was not enough to be detrimental, even to sensitive crops.

The authors added that certain fertilizer regimes may affect soil pH differently under high tunnels compared with open field, and advised growers that soil pH in high tunnels and fields should be monitored and soil amendments adjusted as needed.

The complete study and abstract are available on the ASHS HortScience electronic journal web site: http://hortsci.ashspublications.org/content/47/11/1630.abstract