The April 29, 2023 addition of the OSU Fruit, Vegetable, and Specialty Crop News included a short video summarizing challenges associated with maintaining the productivity of soils in high tunnels (see https://u.osu.edu/vegnetnews/2023/04/29/maintaining-soil-productivity-health-in-high-tunnels-whats-the-problem/). This article focuses on specific examples of those challenges and steps that can be taken to address them from fall to spring.
So, tomato harvest and other chores are complete, and the high tunnel may be taken out of production until next spring. What can be done fall to spring to help maintain or improve high tunnel soil productivity before the next cash crop is established?
First, consider how productivity and profit potential may be lost if nothing is done. Many high tunnels contain tomatoes soon before they are taken out of production in the fall and, chances are, the same high tunnels contained tomatoes for at least one season, if not multiple seasons, before that. Importantly:
a) most core stand establishment, fertilizer/input application, irrigation, and other cultural management practices occur in the same places in the high tunnel each season;
b) fertilizer use can be high;
c) spaces between rows may be covered or uncovered and receive variable amounts of foot and equipment traffic;
d) crops remove major and minor nutrients selectively, in different amounts and ratios; and
e) water lost to evapotranspiration differs by location and depth in the high tunnel.
Combined, these factors can lead to significant variation in soil physical, chemical, and biological characteristics depending on position on the floor (crop row or between) and depth. Crop access to soils with optimal characteristics may be limited. Fertilizer may be present in excess where it does not mineralize. Salt levels may rise where evapotranspiration rates are greatest relative to water supply. Compaction may develop. And, beneficial soil microbial activity may decline or cease due to these conditions and/or a lack of water.
Second, take one or more steps to help correct or limit the development of these and other unwanted soil conditions. For example:
1. Mix soil comprising the footprint of the high tunnel. Move soil past crop row-furrow, if possible, and to below rooting depth. Add organic matter (e.g., green manure, compost) and other key materials (e.g., lime) before or during the process.
2. Consider deep tillage. Past research completed at Penn State Univ suggests that occasional deep tillage in a high tunnel can be beneficial, especially when plow-pans, salt layers, or other symptoms of sub-optimal soil status develop.
3. Regardless of approach, test soil before and after mixing and other interventions, keeping samples separate when submitting them for analysis (e.g., see https://u.osu.edu/vegnetnews/2021/02/20/soil-sampling-and-analysis-for-high-tunnel-production/). Soil test reports from samples taken from the same locations (in and between crop rows) before and after mixing and other steps can be informative.
4. Establish and incorporate a suitable green manure and/or subsoiling cover crop(s) that can perform some of the same functions as machinery and provide many other benefits. Resources for selecting cover crops for high tunnels include: a) https://projects.sare.org/wp-content/uploads/CoverCropsHT-fact-sheet.pdf, b) https://www.sare.org/resources/managing-cover-crops-profitably-3rd-edition/, c) https://www.midwestcovercrops.org/getting-started-correct/, and d) https://mdc.itap.purdue.edu/item.asp?Item_Number=ID-433.
5. Flood the high tunnel slowly. Move water through the profile carefully to dissolve and disperse salts and help mineralize and increase the future availability of remaining fertilizer without contributing to runoff or unwanted leaching. Moist soils may also remain more biologically active, and mix and open pores by freeze-thaw action, providing other benefits. Some of the same benefits of purposeful fallow period irrigation can be achieved by removing the high tunnel cover to allow precipitation and natural freeze-thaw cycles to work for you.
Please contact Matt Kleinhenz (kleinhenz.1@osu.edu; 330.263.3810) with questions or for more information.