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Thursday, October 16, 2014
Day 4- Exit Strategies
When you choose a cover crop for your backyard or your operation, it's certainly important to know the features of it. Will it be good for weed control? Will it provide a quick start? How will it need to be seeded? Equally important is the exit strategy. How are you going to kill it so that you can plant your next crop? The exit strategies will prove to be the one piece that can make growing cover crops the best experience it can be. Experimentation with cover cropping and figuring out which works bests for you is a common practice most growers do. But because you can't kill it shouldn't be the reason that you decide that the cover crop won't work for you.
The Exit Strategy is a term I've picked up from Dr. Ajay Nair of Iowa State who has a fantastic webinar on cover crops in vegetable production that I highly recommend (http://www.extension.iastate.edu/article/webinar-focuses-cover-crops-vegetable-production). But basically an exit strategy is should be determined at seeding. You've got a couple options for killing cover crops which includes crimping, planting within, green manure, winter kill, and cutting. Each of these strategies (and they are even more) have with them pros and cons. Let's delve into these.
Crimping is a method that requires an attachment. The strategy behind crimping is that a tractor attachment can go down a row of a cover crop and hit part of the cover crop that will "crimp" and keep it from growing anymore. Bending it basically. The cover crop will further break down overtime while still assisting with weed management and keeping moisture in the soil. It creates a mat that allows for you to plant right in. Crimping is better suited for grasses such as sorghum-sudan that have a woody quality to them. The problem with crimping as you can tell is that it does require a tractor attachment for it to work. I've used a modified flat board to crimp sorghum-sudan and it worked okay.
Crimping Attachment. Source: organics.utk.edu
The green manure strategy is better for shorter crops. You grow the cover crop and then come through and till it under. Over time the cover crop breaks down and adds organic matter to the soil. This should be done at least 1 month before planting. Green manures also can sometimes not "die" off. This is especially true for a cover like hairy vetch. Green manures though are easy to do in most cases.
Some cover crops will winter kill. So it's possibly to get some very good benefits from mid-August to October and then by winter, these covers will die off. Such covers that will winter-kill include buckwheat, sorghum-sudan, cowpeas, tillage radish, and others.
The most common exit strategy is cutting the cover crop. The aboveground biomass is removed or laid at the side. The underground roots may then be tilled into the soil to break down further. When using a brassica for biofumigation, it's a common practice to remove/flail mow the biomass and then till it under. The roots of the cover crops are breaking down over time and adding organic matter to the soil.
Cover crop that has been cut and laid on soil surface. Source: Extension.org
Most cover crops are suitable to be cut. The biomass can then be added to the soil if you so choose or it's added to your compost bin. Both the green manure and flail mow method take some time to figure out how to work but are not as intimidating as they might seem. Whatever you choose match up the cover crop with the best exit strategy possible for your operation. It doesn't make sense for me to grow sorghum-sudan in my backyard unless I've got the proper tools to get rid of it. Factor in exit strategy at the start of cover crop selection.
Join us tomorrow for the wrap of Cover Crops Week with an overview on Cover Crop Mixtures!