Planting the Cover Crop October 16 2011, 2 Comments
In the Spring and Fall, I watch the big farmers with envy as they head into the fields with their "honey pot" rigs loaded with liquid cow manure. I'd love to be able to fertilize a whole field. Chemical fertilizer is a possibility of course, but it's costly. We have quantities of composted manure from our animals, just not enough to broadcast. So, during the growing season I employ a micro-environment strategy, adding liberal amounts of compost directly to individual hills, rows, and sidedress. Equally if not more important however, is the cover crop.
A fall cover crop benefits soil quality and fertility. The cover crop is planted as soon as the primary crop can be harvested and the ground prepared. My choice is a mixture of winter rye and hairy vetch. The two work together. Vetch is a legume, or "green manure". In simple terms, rhizobial bacteria present in the soil attach to the roots of legumes and convert nitrogen in the air to mineral nitrogen in a process known as nitrogen fixation. Free nitrogen! You can't beat that. The legume with its nitrogen-rich root nodules is tilled-in to the soil before the primary crop is planted. Winter rye is the cereal grain, not to be confused with ryegrass. It is a biomass producing wonder, yielding some 2000 pounds or organic material per acre when it is incorporated in the spring. The rye also serves to support the climbing growth of the vetch. If planted early enough in the fall, the rye and the vetch germinate and establish a root system sufficient to survive the winter. Come spring, the growth is incredibly robust.
After the corn, pumpkins, squash, gourds, and potatoes were harvested, it was time to get in the cover crop. No time to waste either. Rye can germinate and grow at temperatures near freezing, but vetch is more tender. In Vermont, it's always a race to get the primary crop off, and the cover crop in. Weather is a big factor. A seedbed needs to be prepared. Our farm has clay soil. It's fertile, has zero rocks, holds moisture nicely, but is as heavy as concrete. In the fall, I like to use a middlebuster (subsoiler) plow to get down deep and break up the hardpan. Then I till 3 passes to get it smooth and ready for seed. I mix 60% winter rye and 40% hairy vetch, about 80 lbs seed per acre. I've made the mistake of going too heavy on rye and crowding out the vetch. Almost any garden center sells rye seed, but hairy vetch is more a special order. I buy mine from Johnny's Seeds. They have a variety of other legumes, as well as a green manure mix, which uses clover and peas instead of vetch. Johnny's has always been excellent, and I like the fact they are New England based.
A quick word about inoculant. As I mentioned, legumes don't fix nitrogen without the presence of rhizobia bacteria. The plant and the bacteria have what is called a symbiotic relationship. It has to be the right species of rhizobia as well. If you've grown a particular legume in your fields, chances are there is plenty of the natural bacteria in your soil. Otherwise, do yourself a favor and buy the inoculant for your legume seed of choice. If you're not sure, do it anyway. It can't hurt. Most inoculant comes as a fine peat powder. Follow the instructions and quantities on the package. The ideal method of inoculation is to dampen the seed so the powder coats and sticks, but I've had perfectly good results just thoroughly dry mixing it.
I broadcast the seed mixture using one of my favorite garden tools, the Earthway Hand Spreader. I've heard it called the monkey grinder, because of the hand crank. I use it for all types of broadcast seed applications. Any plot under say an acre is perfectly reasonable to do by hand. For uniform coverage, you want two passes across the space, north/south and then east/west. I set the spreader opening a couple notches smaller than I figure for the first pass. That way I don't run out of seed. Ideally, you want to use exactly half your seed on each pass, but I usually end up opening the spreader a little more on the second pass, once I know exactly how much seed I'm putting down. Using the spreader takes a little practice. I get great results walking at a slightly quicker than normal amble, and making a complete revolution of the crank with each full step. That means each time you begin to move your right leg forward, the crank should be at the 12 o'clock position. It's kind of fun. Walk towards a fixed point in the distance, and observe the width of the broadcast so you know about how wide apart to make each walk line.
After the seeding, I make a final trip with the tiller set in the highest position of about an inch or so. You could use a rake too, anything to just to incorporate the seed a little bit with the soil. As I write this, it's been 6 days, and the rye is already germinating. Hopefully, the first hard freezes (low 20's or teens) will hold off until November so the vetch can establish enough root to winter over. Never any worries about the rye. In April, you'll be amazed by the growth and the good you're doing for your soil... all without the expense of chemical fertilizer, or the luxury of having your own herd of cows and a liquid manure spreading truck! Check back for a follow up story on terminating the cover crop.