Vegetable growers who want to get the best soil-health value out of a winter grain cover crop and also plant in May can do so by planting early and terminating early.
An early-kill scenario is sometimes overlooked because spring biomass if the rye is valued. However, vegetable growers can make up for the lack of spring biomass production by increasing growth in the fall. Many vegetables have been harvested by mid-September, so vegetable growers have the opportunity plant the cover crop early. It is difficult or impossible to do so with field crops. The early-plant, early-terminate scenario gets less attention than it deserves as a result. The second half of September provides a lot of growing degree-days for the rye that helps it develop a valuable deep root system through the rest of the fall.
To make a good seedbed, or raised bed, for vegetables, the soil needs to flow well. Sustaining soil health means using the gentlest tillage that will produce conditions for the crop to thrive. Gentle tillage is possible by allowing the succulent cover-crop tissue time to decompose, and the decomposing roots to support soil aggregate formation.
To improve the soil by making better aggregates, it helps to have the roots decompose in undisturbed soil. Decomposing microbes do the work of stabilizing aggregates before those aggregates are broken by tillage. It takes some warmth for that process, so allowing a month between applying the herbicide and doing primary tillage is reasonable.
Small grain crowns can make the soil difficult to fit for planting. Beating them into submission undoes a lot of the soil health benefit of raising the cover crops. The crowns become more durable as they mature and the stems lignify. There is also less time for them to break down before a given planting date. The early kill followed by undisturbed decomposition makes residue that works up much better.
In the example pictured below, rye on the left was killed once it had finished greening up but before any stem extension. But the rye on the right was killed once the stems were about 10 inches long and starting to lignify.
The rye that was killed early decomposed nicely and required only little tillage to work up and bed nicely. The later killed rye had a bigger crown and more straw, and less time for them to decompose. That soil was lumpier, and did not make an even bed edge (arrow).
In this example, only the surface soil was tilled in order to make the beds. The area between the beds was untilled, relying on undisturbed root channels from the rye to aid percolation.
The early-plant, early-kill scenario works for rye, triticale and wheat. The critical steps are easier to execute on time even with weather vagaries, than alternative approaches. The operations are generally faster, cheaper and gentler as well.
These are the steps
- Plant in mid-September to get abundant root growth in the fall
- Terminate just before stems elongate in April
- Allow cover crop to decompose undisturbed until field is prepped.
- Do only as much tillage as is needed.
Published in VegEdge, September 2018