Here's a copy of the presentation that I'm giving at the NY Vegetable Growers Expo this January.
USING COVER CROPS BETWEEN BLACK CORN PLASTIC MULCH AS A MEANS TO SUPRESS WEEDS, INCREASE ORGANIC MATTER, AND GIVE YOU A SOLID REASON TO BUY A FANCY SNAPPER RIDING MOWER.
At Sweet Land Farm we use black corn plastic mulch (biodegradable mulch) for all of our heat loving transplanted crops, as well as a selection of transplanted crops that are in the ground for a large portion of the season. Two of our farming goals are to increase the health of the soil and decrease weed pressure. While using corn mulch is not in our long-term farming plan, we do find it very useful in our current economic circumstance.
First I’ll explain how we use the corn mulch and cover crop, and then I’ll list some pros and cons of the technique. We lay mulch using a rain flo mulch layer with a drip tape attachment. Immediately after the mulch is laid we walk through with a seed spinner and spin out annual or Italian biennial ryegrass. We walk down each path and adjust the seed opening and walking speed to spread the right amount of seed. It is a very fluid process and is done by eye. I aim for a heavy seeding rate – I don’t know the pounds per acre, but the seeds sit about 1 every third inch or so on the soil. I figure the thicker the better – you want a thick, solid cover crop, so over-seeding is cheap insurance. The headlands also get seeded at this time. We seed immediately after laying the mulch because at that point the soil is nice and friable and the ryegrass seeds nestle right down into the soil. With ryegrass we don’t need to cover the seed to achieve germination – a nice plus of ryegrass! If the crew comes through right after the seed is spread (before it starts to germinate) that can help sink the seeds into the soil and aid in germination. If the field is transplanted and then covered with row cover – like our early plantings of kale and chard – germination is assured. To date we have had good germination on all of our ryegrass seedings. We have only used this technique for 3 years, so I’m sure we’ll have some germination failures at some point. We seed all of the mulched fields right after the mulch is laid regardless of whether the field will be transplanted right away or not. In some fields we lay mulch, seed ryegrass, and let the field sit for a time until the cash crop is ready to be transplanted. Once the grass is about an inch high it can take transplanting traffic and recover just fine.
Once the ryegrass is growing and the field is transplanted we mow the grass with a riding lawn mower. We have two riding mowers with 30” decks that fit between the mulched beds. We usually take two passes down each grass path, edging alternate sides on each pass. Always blow the cut grass away from the crops! The number of times you have to mow in the season depends on the crop and the weather. A wetter season means more mowing.
Pros:
If they have to keep working anyway, most people are happy to mow when they are hot and tired. It’s a popular job around here.
After the job is done the farm looks wonderfully manicured, like an English country garden. The visual results are disproportionate to the amount of work. We use mulch in most of our farm’s u-pick fields and it keeps the farm accessible and fancy looking for our CSA members.
The grass does a great job (provided you’ve seeded thick enough) at suppressing weeds. Of course it won’t deplete the weed bank, but it will keep weeds from setting more seed.
The grass eliminates the need for bare soil cultivation between the mulched beds. This preserves organic matter. The grass roots and top growth contribute to organic matter as well as provide a habitat for soil microbes.
After the growing season, depending on the next year’s plan for the field, we will mow the cash crop residue, pull the drip tape, and seed a winter cover crop on the growing bed. The ryegrass will remain intact through the next spring. Nice continuous cover!
We can grow our living mulch on farm rather that buy in straw.
Cons:
The ryegrass needs to be seeded in a timely manner. If the seeding window that occurs right after the corn mulch is laid is missed, it is much harder to get a good seeding because the soil will compact with rain and a transplanting crew, and will need to be re-worked before seeding.
When the grass is mowed the cuttings sometimes are blown onto the crops. This is an issue for some crops and not for others.
This technique won’t work well for a farm with a lot of big rocks. Too hard on the mower.
We have not noticed the grass competing with the cash crop for moisture (we’ve only been here 3 years) but I imagine it’s possible, especially if drip tape was not used.
The grass growth can be extremely rank in a wet year. In the 09-growing season we had plenty of rain and had to mow quite often (maybe once every 2 weeks). On the other hand, we put down more organic matter than usual.
This technique does not work for vining crops such as melons and cantaloupes. We use straw mulch for those crops
We use a living oat mulch in our strawberry fields. In the establishment year we lay black corn mulch and transplant the strawberries. The paths are kept clean with a rear-mounted toolbar outfitted with bezzeride spiders and several shanks. Once the strawberries start to run we pull the plastic and rake the runners (and disturb germinating seedlings) with a one-row belly mounted cultivation tool. The tractor has shanks that cultivate the paths. The runners are raked two to three times, depending on weed pressure (always in the same direction). During this time we keep the paths and bed shoulders clean with the bezzeride tool bar. At the last cultivation before the runners reach lay by we spread oats in the paths. The oats are planted with the last runner cultivation. As with the ryegrass, we seed the oats very thickly with the hand held spinner. The oats lay a least one every third inch on the soil. Thicker is ok. The oats are seeded around August 1st, and continue to grow until they are winter killed. We mulch the strawberries with round bales around Thanksgiving. In the spring we rake the mulch off of the strawberries into the paths. Only a couple of quick hand weedings are required during the fruiting year. Once the berries are finished fruiting we rip the crop down to a narrow growing strip. The berries start to run. From this point on we treat the second year berries the same as the first year. We let the berries bear for two years before turning in the crop. Using the above techniques we have almost weed free conditions in our strawberries.
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