By Alice Percy
MOFGA’s 2006 Spring Growth Conference, titled “Cover Crop and Rotation Strategies for Organic Fertility and Weed Management,” attracted presenters from all over the Northeast and over 100 audience members. Presenters included Eric and Anne Nordell, who operate a horse-powered, mixed vegetable farm in Beech Grove, Penn., and contribute regularly to the Small Farmers Journal, a quarterly focusing on draft-powered agriculture; Eileen Droescher, who has used a permanent bed system to grow mixed vegetables in Easthampton, Mass., since 1999; and Eric Gallandt, an associate professor of weed ecology and management at the University of Maine in Orono.
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| Photo courtesy of the Penn State Agroecology On-Farm Undergraduate Internship Program |
The Nordells elaborated on their philosophy of “Weed the Soil, Not the Crop” (a new take on organic farmers’ adage, “feed the soil, not the crop”). Their system includes annual alternation between production and fallow crops; utilizing short, bare fallow periods; shallow tillage; and – above all – proper timing.
Rotating cover crops with vegetables annually serves the market gardener in several ways. Allowing a cover crop time to mature before it is returned to the soil maximizes its contribution to organic matter. Most organic farmers know that soil with lots of organic matter has better tilth, maintains a proper moisture balance, and generally contributes to the health of their cash crops. The Nordells add that high organic matter discourages what they call “soil-building weeds,” or weeds that flourish in poor soil.
In determining their crop rotation sequence, the Nordells separate vegetables with early planting dates (such as peas and lettuces) and vegetables with late planting dates (such broccoli) into different fields. Each field alternates annually between a cover crop and a vegetable crop, and the vegetable crop alternates between early vegetables and late vegetables, resulting in a four-year rotation (cover crop, early vegetable crop, cover crop, late vegetable crop).
During a fallow season, each field bears two cover crops: the overwintering one that is planted after harvesting the previous year’s vegetable crop, then one that is planted in midsummer that may or may not winterkill, depending on the vegetable crop scheduled for the following year. Between the two cover crops, the Nordells utilize a six-week bare fallow period to kill perennial weeds and to reduce the annual weed seed bank.
The Nordells have developed a sense of timing that comes with experience and a sensitivity for the special requirements of their locality. Where they live, they can plant winter rye in the second week of August and it achieves good growth before entering winter dormancy, and this is late enough that broadleaf weeds that germinate with the rye are winterkilled before they set seed. Dates will differ in Maine.
A Four-Year System in Maine
Eric Gallandt explained a university-sponsored, four-year cropping systems trial that compared effects of several sets of cover cropping techniques on crop yield and soil health. Highly variable weather patterns during the trial confounded crop yield data, so Gallandt warned that the yield results may not be very reliable. He also cautioned that large differences in many soil quality parameters were difficult to see during the relatively short study. “If you want fast results, use lots of compost,” he advised.
The “control” system used no cover crops, relied on ammonium nitrate fertilizer and on herbicides, and alternated annually between broccoli and squash. In 2005, this system yielded by far the least broccoli. By the end of the trial, the soil in this plot had a much denser texture and significantly less capacity to retain moisture. Weed biomass was measured in the fall each year and varied a great deal, although the biomass of lambsquarters increased annually.
The “land-limited” system also alternated annually between broccoli and squash, but relied on blood meal for nitrogen during the years the broccoli was planted, and included a rye/vetch cover crop after cash crops were harvested. This system yielded much more broccoli than the control but much less than the other two cover-crop systems. Due to multiple soil disturbances each season, this plot experienced the greatest total decrease in weed biomass over the four years.
The “low-disturbance” system left a clover/oat cover crop on the soil for two years, followed by one year of broccoli and one year of squash, with blood meal supplying nitrogen to the squash. This plot yielded the greatest amount of broccoli, but only slightly more than the “summer fallow” plot. This system also resulted in the greatest quantity of stable organic matter due to the long-standing root system of the cover crop. The total weed biomass was fairly high and decreased the least under this style of management, because the soil was rarely disturbed.
The “summer fallow” system very closely resembled the Nordells’ system, using rye, oat/pea, and oat/vetch cover crops. This system consistently outranked the others in squash production. It was the only system in which the population of lambsquarters – a weed that is difficult to control – did not increase, and the total weed reduction was second only to the land-limited system. The total fall weed biomass under the summer fallow system was consistently much lower than that in the other plots.
Permanent Beds and Custom Equipment
Eileen Droescher of Ol’ Turtle Farm uses a cover cropping and permanent bed system similar to Gallandt’s “low disturbance” techniques. Her custom-built equipment fits her system – a 4-foot flail mower (with wheels that run in pathways between beds) to control cover crop growth and a manure spreader adapted to fit the beds and to drop, instead of throw, compost onto just the bed area. Planting is scheduled to leave a cash-crop section between two sections of cover crops, providing habitat for beneficial insects and a catch crop for pest insects, as well as pasturage for laying hens. By keeping careful records, Droescher can assure that she waits at least three years before planting a crop from the same family in a particular bed. The alternating beds also provide a pleasant landscape and help her CSA customers understand her farming techniques.
Alternative Tillage
The Nordells ended the day by discussing some of their alternative tillage techniques. Reduced tillage, they asserted, maintains better soil structure – a crumbly texture rather than the pulverization that results from aggressive rotovating. Better soil structure means better moisture control during any weather. In conventional circles, “reduced tillage” often means increased use of herbicides, but the Nordells restrict themselves to cover cropping and to creatively using mechanical cultivation. Their cover crop system requires multiple soil disturbances, reducing weed pressure but risking degrading the soil texture. Their solution is to minimize the depth, rather than the quantity, of tillage. Deep tillage might be appropriate under certain circumstances, such as preparing established turf for farming or eradicating deep-rooted perennial weeds. Usually, however, deep tillage only encourages weed seed germination and over-accelerates organic matter decomposition. And, of course, the Nordells rely on draft animals to power their equipment; the “shifting plate” action of horse hooves tends to loosen soil instead of compacting it, as tractor tires can in some conditions.
The collected evidence throughout the day was a powerful testimonial to the utility of cover crops on the organic farm. This author, at least, was left eager to go home and sow some oats.
About the author: Alice Percy and her husband, Rufus, own the Treble Ridge Farm in Whitefield. They alternate land between pig pasture and vegetable crops and use cover crops to hold soil nutrients left by the pigs.
