For many vegetable farmers and gardeners, there’s something supremely satisfying about a cleanly tilled field in spring. It represents a new beginning. The weeds haven’t started growing yet, the soil is fluffy, and it’s easy to put seeds and transplants in the ground. Despite the short-term benefits of tillage that can help vegetable crops grow, tillage takes a toll on soil health by destroying soil aggregates, making soil susceptible to erosion, compacting subsoil, and “burning up” organic matter. The more you till a soil, the more it needs tillage to get back to that temporary fluffy state. Targeted use of cover crops can break this cycle of tillage, creating windows for no-till production that can rebuild soil health over time.
For the last three years, we’ve had success at the University of Maryland and with participating farmers with no-till seeding early vegetables like spinach, peas, and beets into a winterkilled forage radish (Raphanus sativus L.) cover crop without the use of herbicides. The inspiration for this work came from previous research on forage radish in agronomic systems that showed its roots have the ability to penetrate compacted soil layers, its dense fall canopy can suppress nearly all early spring annual weeds, and its residue decomposes rapidly in spring, leaving a nearly bare seedbed full of nutrients.
Conscientious farmers and soil scientists alike may cringe at the thought of bare soil (aren’t we supposed to keep it covered?), but this aspect of the seedbed after forage radish is an essential component of its ability to replace tillage. Cold, wet soils in spring can hinder crop production and field work, and the relative lack of residue after forage radish allows the surface soil to warm up and dry out, creating a hospitable environment for vegetable seed germination. Lower soil water content also reduces the potential for soil compaction from driving on the field if a tractor is used for seeding. (On Pasture has also covered the use of radishes as pasture improvement and forage.)
After concluding that no-till seeding early vegetables after forage radish is an effective crop production strategy in the mid-Atlantic, I took this system north to Maine, where soil warming in spring is an even bigger concern. This year, there was snow on the ground well into April. In agricultural research, we like to see something work more than once and under many different conditions before we arrive at conclusions, but I will say that I am encouraged by my no-till seeded spinach and peas, and even my no-till carrots in the sandy soil at my one site in Maine. This may be a no-till technique that works for some vegetable crops in some soils in northern climates where cold soils can really hinder crop growth.
The window to utilize the benefits of a forage radish cover crop is limited. Weed suppression after forage radish does not last forever, and because the nutrients from decomposing forage radish tissue are available early in spring, they may have been lost from the topsoil by the time a later-season crop is planted. For later-season crops, a different cover crop approach is necessary; researchers and farmers have been working on high-residue systems for later-season no-till vegetable production for the last couple of decades.
High-residue cover crops, like a rye-vetch combination, overwinter and continue to put on a lot of biomass in spring. As the cover crops begin to flower, they can be killed mechanically. The resulting mulch suppresses weeds and keeps moisture in the soil. Finding the right balance between rye, which suppresses weeds effectively but ties up nitrogen, and vetch, which doesn’t suppress weeds well but makes nitrogen available, can be tricky. This system can be effective for later-planted tomatoes, Brassicas, and other transplanted crops in the mid-Atlantic.
These two cover crop-based no-till systems fill very different cropping niches, but they have some commonalities that are important to note in order to implement them effectively and to develop new cover crop-based no-till systems, which we hope will proliferate in the future!
Plan ahead. Seeding date for both of the systems discussed above is critical to get the full benefits. In the mid-Atlantic, forage must be seeded before the first week in September. To get good biomass, rye-vetch must be seeded before September 15. Dates for regions further north are earlier.
- If you want your cover crops to make you money, treat them like your cash crops. Cover cropping can’t be an afterthought. If possible, give your cover crops the same care in seeding, irrigating, and sometimes even a boost in fertilizer to allow them to perform their best and actually work for you.
- Equipment needs may change. Seeding or transplanting into an untilled seedbed may not work with traditional equipment and weeding may present new challenges. But don’t be afraid, just
- Start small and have a control treatment. Sometimes we can talk a good game, but it’s always best to try something on a very small scale for yourself the first time. And make sure you keep a strip of your “usual” treatment so you can actually compare the new to the old.
More details on the do’s and don’ts, the lessons we learned, forage radish, and cover crops and no-till vegetable production can be found at our website www.notillveggies.org.