Maintaining High Tunnel Rotations,
Soil Fertility & Soil Health
Adapting annual crop production rotation practices for high tunnels in ways that enable growers to maintain soil fertility and health is not yet completely worked out. There are few well-established rotation recipes, and every grower needs to put in place a rotation plan that works for them, using resources available.
For example, using cover crops with fallow seasons in tunnels is inconvenient both in timing and practice. Alternatives to this include the following management tactics:
- Regularly incorporate soil amendments like composts into high tunnel soils. Using composts maintains fertility and soil quality and avoids the need for cover crops with inconvenient fallow periods, but may be cost prohibitive.
- Move the high tunnels every few seasons to nearby or adjacent fields where cover crops and/or soil amendments (manures, composts, or un-composted municipal leaves) were aggressively used on fallowed soil.Due to existing tractor and implement sizes, it is frequently much easier to grow and incorporate cover crops and amendments in open fields, and periodically relocate tunnels. This is much more efficient than performing these rotation and soil fertility building practices inside the tunnels and losing production seasons to fallow periods.
- Select crop varieties resistant to common pathogens in your area.
- Use soluble fertilizers injected through the drip irrigation system.
- Use bag culture when appropriate to the crop to avoid disease or fertility problems.
- On crops like tomato, use grafted plants when growing crops for more than one season in the same area, until moving the tunnel.
A Sustainable Rotation for Grafted Tomatoes
Grafted tomato crop rotation is an example where the prevailing recommendations have not yet caught up to the practice of farming. USDA NOP regulations may not yet consider alternatives to annual cycle of rotation to be acceptable biologically based farming practice recommendations. However, grafted plants really should be an exception to this regulation because they have characteristics that solve an important problem and one of the reasons we traditionally perform crop rotation annually.
Crop rotation is done for two reasons: growing the same crop year after year in the same soil leads to a build up of diseases affecting that crop, and depletes soil nutrients. Increased disease load and nutrient depletion both lead to “diminishing returns” i.e. decreasing yields and decreasing profits as a result of poor soil health. However, due to reasons of efficiency – growing the same crop in the same place for more than one season may be desirable.
A crop rotation recipe is emerging for grafted tomatoes that combines their disease resistance and other characteristics with the benefits of high tunnels that provides both increased profits and improves soil health.
This recipe is grounded in the following practices:
- The tunnel will be moved on a +/- three-year cycle.
- The soil where the tunnel will be moved to is aggressively cover cropped and amended (with manures, compost, or un-composted municipal leaves for example).
- The cropping scheme is such that grafted tomatoes are grown no more often during the extended cycle than they would have been grown with in that area with an annual cycle.
For example, an annual cycle looks like this – tomato, other, tomato, other, tomato. The extended cycle looks like this – tomato, tomato, tomato, other, other. Over the extended 5 year cycle, grafted tomatoes are not grown in that field any more than they would have been grown using an annual cycle.
Novel approaches to crop rotation, such as this, need to be developed for sustainable farming in our state.
A Sustainable Rotation in Practice for soil health & fertility
Through the years, the Muth farm has gained recognition as one of the leading regional farms in sustainable agriculture. The use of un-composted leaves and long fallow periods are key practices. Farmland application of 6″ mulch layer of un-composted municipal collected leaves plus cover crops 2-3 years in advance of relocating high tunnel provides time to improve soil fertility and health, avoids nitrogen immobilization, while still working efficiently with larger equipment.