Cultivating Questions

Concerning the Bio-Extensive Market Garden

by Anne & Eric Nordell of Trout Run, PA

Dear Anne and Eric,

I just finished reading your booklet of articles and I wanted to write to you to let you know how much I enjoyed reading it and to ask you a few further questions.

I am beginning my second season on a horse-powered, whole-diet CSA farm in Western Massachusetts and your articles are the most relevant, replicable sources of information we have found. Your writing is specific, but not restrictive, allowing us to modify your innovations to fit the constraints of our farm.

This winter, we created a four-year rotation, with groups based on planting date, and are going to try rotating tillage depth and bare fallow periods as well. This is much further ahead than we’ve ever thought before! So thank you!

I have two questions lingering after reading your articles – What have you observed soil-healthwise is the difference between mowing versus grazing down a cover crop?

My hypothesis is that like everything else, it is probably good to rotate techniques. To first mow, then let re-grow, then graze and incorporate both the decomposing cover crop and now the fresh manure. But is there a net-loss of nutrients through grazing? What beneficial additions does the animal create through digestion that cannot be accomplished through mowing?

My other question pertains to the spreading of finished manure. In your experience, when is the best time to spread manure and where in the rotation? Onto a well established cover crop that is then tilled in? On a bare fallow section before seeding down a cover crop? And what time of year? In order for maximum nutrients from the manure to be retained and taken up by the cover crop.

I would love to hear your opinions on these questions – whether it be through a note or the recommendation of an article (perhaps you have already written one!) but if this is a busy time of year for you, no rush.

I am falling in love with horse farming and looking forward to years of experimentation and mistakes and writing to others about these discoveries!

Thanks for all you do. With admiration and inspiration,

Rose Cherneff

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Mowing Versus Grazing the Cover Crops

We agree with Rose that rotating everything – crops, cover crops, tillage techniques and compost applications – is usually the best strategy. However, we have not tried rotating between mowing and grazing the cover crops due to logistical challenges. It is not convenient for us to graze the work horses in the fallow lands because of the distance between the stables and the market garden and negotiating the harvest lanes and deer fence with horse fencing. Also, many of the annual cover crops that we grow are not suitable for horse forage, and we are concerned about compaction and uneven distribution of manure from pasturing the horses.

If we wanted to graze large animals in the market garden, we would change the bio-extensive rotation from alternating years of vegetables and annual cover crops to 3-4 years of produce followed by 3-4 years of grass-clover pasture. This perennial cover crop would be much more suited for grazing, reduce the likelihood of compaction, and improve soil quality through a much more extensive root system and the elimination of tillage. Drawbacks might include the buildup of weeds, wireworms and grubs, and making the transition from a long term sod to market garden vegetables.

We could imagine that pasturing the bio-extensive market garden would be very compatible with a whole diet CSA which raises a diversity of livestock and grows corn for animal feed, the traditional crop following pasture or hay. No doubt minerals would be removed from the soil with the sale of the animals, but this may be an advantage if fertility is high due to years of applying compost. Also, the inoculation of the soil with beneficial microbes via the animal’s digestive process and mucous secretions could more than offset these small material losses. Like so many decisions in agriculture, choosing between mowing annual cover crops and grazing perennial pasture really depends on the needs of the land and ease of management for the farmer.

Timing of Compost Applications

The same could be said for the timing of compost applications. We hedge our bets by applying the horse manure compost at different times of year and different stages of the cover crop life cycle to enhance growth and/or decomposition. Using relatively small amounts of compost to amplify the soil building effect of the cover crops allows us to maintain soil quality in the market garden with the manure from a few work horses.

This piecemeal approach to compost application is partly a function of our batch system of composting. With a new batch ready for spreading every 6-8 weeks, it is easier to load the spreader directly from the compost middens in the stables and apply it to the cover crops than to stockpile the material and spread it all at once in the spring before planting the vegetables.

The “Weed the Soil” DVD depicts the basic compost rotation: applying compost in the summer of the fallow year to enhance the growth of the winterkilled cover crops in preparation for EARLY planted vegetables the next year; and spreading compost late fall or early spring on an overwintering cover crop in preparation for LATE planted vegetables. Applying the compost well in advance of planting the produce complies with organic certification (and food safety) standards for compost that does not meet the NOP requirements. It also allows this unfinished compost plenty of time to decompose before the vegetables go in the ground. Our impression is that the undigested material in our 6-8 week compost provides more food for the soil life than applying a finished product.

As for the batches of compost that are ready for spreading in late spring, early fall and midwinter, we apply this compost before or after planting cover crops in the fallow lands that will be used for (or have been used for) mulch production. Since switching to the pasture manure compost system described in the Spring 2014 issue of SFJ, we are generating significantly more compost with fewer horses. Almost half of this compost now goes to the cover crops used for mulching the vegetables.

How Many Horses Does it Take to Fertilize an Acre of Vegetables?

How much compost to use for growing produce may be a more pressing question for many growers than the timing of application. Soil testing, crop recommendations, nutrient budgeting and field observations are some of the common methods for determining compost rates. Although we have used all of these tools over the years, our guiding principle has been kind of arbitrary: we use the manure produced by our work animals. With three to four horses for 3 ½ acres of vegetables, that comes to one horse per acre and a current application rate of 5-6 tons/acre.

We were interested to read in Ken Laing’s excellent article on “Practical Horse Farming” in the Winter 2014 DAPNet newsletter that he also uses the 1:1 rule of thumb at Orchard Hill Farm in St. Thomas, Ontario. In Ken and Martha’s case, seven Suffolks provide all the manure for their seven acre CSA. To be more precise, the manure collected from each horse over the course of a year results in 5 tons of finished compost, just the right amount for an acre of most vegetables.

To see if other horsepowered farms were using this 1:1 ratio, I contacted the teamsters who participated in the work horse accounting project (see “Portraits of Four Horsepowered Produce Farms” in the Summer 2012 SFJ). David Fisher of Natural Roots in Conway, MA estimates that each of his five work horses produces 7 ¾ tons of unfinished compost. His compost rate for the 3 ½ acre CSA ranges from 6-10 tons/acre.

At the lower rate, each horse could fertilize more than an acre of vegetables. At the higher rate, David buys in finished compost for some of the vegetable land as a significant percentage of the horse manure is used on pasture and hay ground – 22 tons in 2013. Due to the porous nature of the sandy soil at Natural Roots, it is sometimes necessary to sidedress the vegetables with a high nitrogen organic fertilizer after heavy rains. He also uses foliar feeding on many of the crops.

Keep in mind that Orchard Hill, Natural Roots and Beech Grove use the 1:1 rule for soil restoring cover crops. All of us set aside enough land to grow an acre of cover crops for every acre of vegetables. All three farms also supplement the compost with macro and micro minerals lacking in the horse manure and/or the soil, such as calcium, sulfur and boron. Without this land extensive approach to market gardening and the addition of rock minerals, more compost – and more horses – may be necessary to maintain soil quality and fertility.

For example, Stephen Leslie of Cedar Mountain Farm in Hartland, VT rotates three acres of produce with one acre of cover crops and does not buy in soil amendments. His current application rate is 16 tons of compost/acre. Because the manure from the four Fjords is composted with the manure from their 20 cow dairy, it is not possible to determine how much land each horse fertilizes.

The length of the growing season and native fertility of the soil may also influence the application rate. Paul Hauser of Maple Hill farm in the fertile farm land of Chester County, PA is able to maintain the productivity of his five acre market garden without taking land out of production or buying in supplements. He relies entirely on the manure from his three horses, two cows, and 325 layer hens, amounting to 18 loads of fresh manure per acre with his New Idea 14-A manure spreader. He estimates that a horse could fertilize 1 ? acres of vegetables if stabled year round.

None of the farms in this impromptu survey turned out to be fertility self-sufficient. Maple Hill takes advantage of free mushroom compost for growing hay and grain. Orchard Hill trucks in 40 tons of composted turkey manure to improve the land used for hay and grain production. Natural Roots buys in compost and organic fertilizers for vegetable production. We purchase rock minerals for our extensive horse pasture and buy in all of the hay, grain and bedding for the horses. At Cedar Mountain, nutrients are imported with purchased hay and grain for the dairy and exported with the sale of compost to local growers.

Based on the horsepowered market gardeners in this small study, application rates can vary from 5 to 16 tons of compost/acre depending on the type of soil, intensity of cover cropping and use of other soil amendments. This casual survey also indicated that while the 1:1 rule might serve as a reasonable goal, it only holds true in certain situations . . . and if the horse is not expected to fertilize the vegetables and his own food. Although it may be possible to close the loop by rotating the produce with horse forage and feed, few animal powered farms in the Northeast have enough prime vegetable land for this extra-extensive layout.

How Many Acres Does it Take to Grow a Ton of Compost?

Brian Caldwell’s “Land Usage for Organic Vegetable Cropping Systems” adds another dimension to the closed loop challenge. Noting that many organic vegetable producers rely on imported compost, he decided to measure the footprint of dairy manure compost. His preliminary calculation: .35 acres of dairy feed and forage per ton of compost. For the market gardener applying 10 tons/acre of imported dairy manure compost, 3.5 acres are required to grow the fertility for each acre of vegetables.

When I mentioned the compost footprint concept to Stephen Leslie, he was very interested in determining the ghost acreage for the 600 tons of dairy-horse manure compost produced annually at Cedar Mountain Farm. Using his best estimates for forage acreage (72 acres of their own hay and pasture plus another 72 acres for purchased round bales) and my creative calculation for the 80 tons of bought-in dairy and horse grain, we came up with a total land base of 180 acres and a footprint of .3 acres for each ton of compost, very similar to Brian’s speculation for a conventional dairy.

However, pine shavings are an essential component of the bedding pack used at the Cedar Mountain dairy. Assuming an annual sustainable harvest of ½ cord/ acre for the 850 yards of purchased pine shavings used each year, another 120 ghost acres must be added to the fertility land base, increasing the compost footprint to .5 acre/ton. At Stephen’s current application rate of 16 tons/acre in the market garden, each acre receives 8 ghost acres of compost on an annual basis.

Paul Hauser grows all the grain, forage and straw for three work horses and two milk cows on 14 acres. Including the 14 ½ tons of purchased feed for the 325 layers expands his fertility footprint to 20 acres. Since all of the manure is spread on the five acre market garden, it takes four acres to fertilize every acre of vegetables.

David Fisher’s fertility land base is very similar: 18 acres of hay and pasture plus the equivalent of 1.6 acres for the 2 tons of purchased oats. Instead of buying in straw, he now beds the five work horses with low quality hay and the sawdust generated from his portable saw mill. The compost footprint at Natural Roots covers .5 acre per ton or 3-5 acres per acre of produce at a compost rate ranging from 6-10 tons/acre.

Our fertility footprint is a size 14 by comparison. With 18 acres of steep sidehill pasture for just 3-4 horses and the equivalent of 6 acres for purchased hay, grain and bedding, our annual production of 35 tons of pasture manure compost is haunted by 24 ghost acres or .7 acres/ton. That translates into 3.75 acres to grow enough compost for one acre of vegetables at our current application rate of 5-6 tons/acre. However, our compost footprint for each acre of produce is actually double that if we take into account the compost used in the fallow fields to enhance cover crop mulch production.

The Laings’ compost footprint for vegetable production is also 7.5 acres with the major difference that they grow all the feed and bedding for their seven horses. The 22 acres of hay, 10 acres of small grains and 22 acres of pasture at Orchard Hill produces 35 tons of finished compost at roughly 1.5 acres per ton.

In summary, this handful of horsepowered market gardens use anywhere from 3 to 8 acres to grow enough compost for an acre of vegetables and much of this compost acreage is fertilized with off-farm inputs. Although this must seem like sobering news for closed loop sustainability, compared to the fossil footprint of chemical fertilizer and CAFO manure, land usage for animal powered organic production is much more transparent. We can easily account for the ghost acres of compost production and find tangible ways of shrinking our compost footprint such as having the discipline to spread an increasing percent of the horse manure on the hay ground and pasture, by scavenging on-farm sources of bedding, and – coming back to Rose’s initial question – rotating the vegetable land with perennial pasture whenever possible.