One of the most perplexing challenges of my Sub Acre Agriculture project will be to consistently and sustainably increase fertility in the soils to optimize yields over time. While this can be done exclusively through green manure cover crops, it is more efficient to combine a planned cover crop rotation with livestock manures. Andy Lee states in his book Chicken Tractor, that while he was at Intervale Center in Vermont he saw yields increase in one year with manure to the levels it took 4-5 years with (very) heavy compost applications. As this system is designed to be used in small landholdings, specifically medium to large Suburban yards, traditional livestock such as goats, horses, and cattle are not really an option. That leaves smaller critters -specifically poultry and rabbits.
Rabbits are a great option if you want to eat them for meat: they breed like, er, rabbits, they have manageable feed needs, and their manure is “cold” which makes for great vermi-compost and can even be directly applied to your beds (though wait before applying raw manure to any food crops!). If, like us, you are not into eating your livestock you may go the route that Patti, the Garden Girl has chosen and raise Angora’s for fiber while still getting all the fertility benefits of the manure. She keeps them in rabbit “tractors”, portable pens that are sized to fit in her small raised beds so they apply their manure directly onto her gardens. Slick! Plus they are dang cute and very gentle around little ‘uns. Think of them as a functional petting zoo!
We will be using chickens as I want to leverage several very useful attributes of being a chicken: scratching for food, pooping, laying eggs, and eating bugs. When confined to a small space, chickens will scratch to bare soil in their search for seeds and critters, all the while manuring as they go. In a traditional chicken pen this leads to hardpan and toxic levels of nitrates which can kill the soil. The trick is to let the chickens stay put long enough to prep the ground without damaging it-in other words you need to move the birds. Enter the Chicken Tractor. Much like Patti’s rabbit tractors, chicken tractors are moveable pens that house, feed/water, and protect the chickens while confining them to a specific area. In our case the beds are planned to be 3×40’. So our “tractors” will be 3.5′ x 12′-ish with roughly 10′ exposed to the ground allowing the birds to be moved down the beds eating, scratching, laying, de-pesting, and manuring as they go. The tractor will be mounted on 2×4 skids, perhaps with wheels on one end if it gets too heavy -I want it to be one person portable, and will be wrapped in poultry wire with a hutch for laying on one end.
Initially the Sub Acre Market Garden was designed to include the chickens within the rotation-moved as needed to strip off a crop and prep the ground for the next. This was proving to be very complicated: Where would the chickens go from late June to August when the majority of the beds were in crop? Would the chickens be able to scratch down the perennial covers like red clover? How in the heck would I maneuver the tractor into the middle of a diversified bed? Lots of problems. Thinking within this rotational framework was proving fruitless, and was sapping critical time and energy, so I broke down the rotation and rethought it from scratch. The solution I came up with was permitted by the fact that I have virtually unlimited space at the farm (20 acre farm, .1 acre garden). I now plan on laying out 2 gardens that mirror each other. The first will be tilled this spring with the 48″ tiller on the owners Kubota -this should be the only time that tines hit soil in this project. The beds will then be planted on a modified rotation, basically removing the perennial covers (Red Clover/Alfalfa) that were intended to add fertility-replacing them with the missing legumes like dry and snap beans. Covers will still be used, but they will be annuals like buckwheat and oats to keep the soil covered in between plantings in the Spring/Fall beds. Come fall the beds will be sowed with a rye/vetch or other winter hardy mix.
Meanwhile in the “mirror bed” will be the more locus for actually building fertility. Cover crops, unless left in for more than a year, typically only maintain fertility when used in a vegetable rotation. Taking the “mirror” bed out of production will allow it to be under cover for a full year, building critical root systems, while also adding fertility and building soil ecology through active additions of animal manures. Goal is to add at least .25% organic matter each rotation. Not only will this boost yields, it will also sequester roughly 2.5 tons of CO2 per acre!
To get things going, I will do a rough sheet mulch to remove the pasture grasses, and that will then be planted with a PVO mix (Peas, Vetch, Oats) on parts and Sudangrass on others to build fertility and smother any remaining plants. Planting both (and any others that you can recommend) I will be able to experiment with a variety of crops for ease of incorporation and their ability to sync with this system. Into this I will use a system of mowing (hopefully with my new scythe!) then chicken tractoring to harvest the lush growth and manure the beds all year. The chickens will be moved frequently enough to not kill the mixes until late in the season. Seeing as both the PVO mix and the Sudan Grass are capable of putting on 4 tons of biomass per acre I should have plenty of extra growth for supplemental on site composting to provide compost for our Eco Victory Garden projects. In 2009 these beds will be prepped for the veggie gardens that will rotate over. Beds that will hold early spring crops will be fall planted with a crop that winter kills like Oats. The mirror beds may also be used to grow winter fodder for the chickens by letting some oats go to seed. Making the paradigm shift to the Mirror Beds has completely freed my thinking to move onto other, more practical matters like Chicken Breeds, veggie cultivars, pen design, and problem solving how the heck I plan to grow 1000 transplants without a greenhouse! Expect a flurry of posts on these topics in the coming weeks before I start being forced to spend less time posting and more time doing.
I have already begun meeting with my restaurant clients to get their inputs and commitments. 2008 is shaping up to be a great year! To say that I am stoked for Spring is a huge understatement!
-A very excited Rob
Be the change!!