Cultivating Questions

Concerning the Bio-Extensive Market Garden

by Anne and Eric Nordell of Trout Run, PA

The Organic Cropping Systems Experiment at Cornell

Do you know of growers who have adopted the bio-extensive system?

The short answer to this recurring question is Yes! We can’t pin down the exact number, but we have crossed paths with quite a few vegetable farmers who have implemented the bio-extensive principles or have independently developed similar land-extensive practices.

For example, two growers in New York who adopted our alternating fallow year system reported a tenfold reduction in hand weeding onions after only three years. A CSA farmer in Massachusetts also saw a rapid improvement in crop yields and weed control after implementing the bio-extensive system. She cleverly adapted our horse-powered methods to minimize compaction with tractors by designing a permanent bed system which utilizes the same wheel tracks for managing the cash crops, cover crops and bare fallow periods.

Recently we met a bio-extensive Amish farmer who led a soil management workshop at the Northern Michigan Small Farm Conference. He tried out our system, including some of our reduced tillage practices, after attending our presentation at the same conference five years earlier. Although he had to adapt the cover crop rotation to his soils and climate, he emphasized that taking land out of production for cover cropping was the key to quickly transitioning his conventional produce operation to biological management with a minimal reliance on off-farm inputs.

We must confess that we only know of a handful of growers who have claimed such rapid results from switching to bio-extensive market gardening. The payback on taking land out of production has been much slower for others.

This has also been the case for a research project that implemented our system at Cornell’s experiment station farm near Freeville, NY. Although the challenges of adapting bio-extensive practices to a research setting are very different than farming, the Organic Cropping Systems project (OCS) provides a unique opportunity to study the tradeoffs of going bio-extensive when the payback may be deferred for more than a half dozen years.

This long-term cropping systems project is a collaborative effort between researchers, extension and farmers. Funded by the USDA Organic Agriculture Research and Extension Initiative, it explores the essential premise of organic farming, namely, the connection between healthy soil and healthy crops. Specifically, the OCS program, which includes long-term organic grain and vegetable experiments, tries to evaluate how varying intensities of cropping, cover cropping, tillage and compost affects soil quality, nutrient levels, insects, weeds, disease, yields and profitability.

We will provide a full report on this multifaceted project following the completion of the second cycle of the four-year vegetable rotation. For now, we will limit ourselves to a brief description of the four different vegetable systems with a focus on how the bio-extensive treatment is faring six years into the experiment.

System 1

• year 1 – rye cover crop followed by sweet corn (first rotation) or winter squash (second rotation)
• year 2 – snap peas followed by fall cabbage
• year 3 – lettuce followed by fall spinach
• year 4 – potatoes followed by rye cover crop

System 1 is intended to represent an intensive cropping system that might be used to maximize productivity by a land-limited market gardener. This treatment relies on relatively high rates of dairy manure compost to insure plenty of fertility for growing six vegetable crops over a four year period. Application rates are based on the nitrogen needs of the crops, ranging from 6-10 tons of compost/acre per year.

System 1 uses intensive tillage (moldboard plow, rotovator and/or springtooth harrow) to prepare clean seedbeds for the succession of cash crops and to facilitate mechanical cultivation with a Rabewerk tine weeder and a belly mounted cultivator set up with vegetable knives and sweeps. The primary purpose of cultivation and hand weeding is to insure good crop yields. No attempt is made to “weed the soil” with bare fallow periods or by removing weeds that might go to seed.

System 2

• year 1 – wheat and hairy vetch cover crop followed by sweet corn/winter squash
• year 2 – oat and forage pea cover crop followed by fall cabbage
• year 3 – lettuce followed by buckwheat and clover cover crop
• year 4 – clover preceding potatoes followed by wheat and vetch cover crop

System 2 represents a market garden situation where both land and compost are somewhat limited. The goal of this treatment is to produce a cash crop and a substantial cover crop containing a nitrogen-fixing legume every year. Comparatively low compost application rates of 2-5 tons/acre take into account the estimated nitrogen contribution of the legume cover crops. Systems 2’s tillage and weed management are the same as System 1.

System 3

• year 1 – clover cover crop preceding sweet corn/winter squash followed by rye cover crop
• year 2 – rye cover crop preceding summer fallow followed by oat and forage pea cover crop
• year 3 – winterkilled oat and peas preceding lettuce followed by buckwheat, fall bare fallow and cover crop of rye
• year 4 – rye cover crop preceding summer fallow followed by buck wheat and clover cover crop

System 3 simulates a farm where labor and compost availability are more limiting than land. This bio-extensive treatment produces only two cash crops over the four-year rotation. The alternating fallow years are devoted to cover crops and bare fallow periods to restore soil structure and intentionally deplete the weed seedbank in the soil.

Weeding the soil is also accomplished by a cultivated fallow before or after the vegetable crops, removing all weeds that might go to seed, and, whenever possible, limiting the depth of tillage. Nutrient management for System 3 is similar to System 2 with compost application rates ranging from 2-5 tons/acre per cash crop.

System 4

• year 1 – hairy vetch and winterkilled oat preceding sweet corn/winter squash
• year 2 – oat and forage pea cover crop preceding fall cabbage
• year 3 – lettuce followed by oat and forage pea cover crop
• year 4 – winterkilled oat and peas preceding potatoes followed by oat and hairy vetch cover crop

The goals and design of System 4 are similar to System 2 with the added twist of using continuous ridge-tillage to improve soil quality, restrict compaction, manage the weed seedbank, and synchronize nitrogen release with crop growth. System 4’s nutrient and weed management objectives are identical to System 2 except that specialized equipment and a different cover crop selection are required for ridge-till seedbed preparation and mechanical cultivation.

Similar to the experience of some growers who have tried bio-extensive market gardening, System 3 has not achieved a miraculous reduction in weed pressure during the first six years of the OCS experiment. Although the System 3 plots look noticeably less weedy than the other treatments, the seedbank data analyzed to date for entry point 1 has not shown a significant drop in the total number of weed seeds.

Of more practical consequence, the focus on weeding the soil has not translated into lower labor costs for weed management. To the contrary, System 3 has the highest labor requirements in the experiment due to the extra fieldwork for fallow year management and the added hand weeding necessary to remove all the weeds that threaten to go to seed in the cash crops.

One reason that substantial savings in labor for weed control may take longer to realize at the Freeville experiment station is the much higher initial weed pressure at this site than we faced on our farm. To make bio-extensive management even more challenging, the Freeville soil contains large numbers of persistent summer broadleaf weeds (particularly pigweed) and winter annuals (primarily chickweed). Developing a suitable rotation of cover crops and bare fallow periods to match the life cycle of this combination of weeds has been an ongoing challenge for the research team.

Differences in equipment and soil conditions have also added to the learning curve. For instance, it took four years to realize that shallow rotovation was a more suitable form of minimum-depth tillage than skim plowing or discing the rocky ground at Freeville with a tractor.

An entirely different implement-related weed challenge has been noted by Chuck Mohler, the OCS Project Director for the first six years of the experiment. Due to the small (25’ by 65’) size of the randomized, replicated plots, weed seeds may be entering System 3 on the tractor tires and machinery.

Finally, the high soil fertility at Freeville may favor the weeds much more than the very low nutrient levels we started out with on our farm. For all of these reasons, two or three cycles of the bio-extensive rotation may be necessary before receiving a payback on the extra land, labor and management required for weeding the soil.

The good news is that the OCS experiment shows that bio-extensive market gardening can be profitable despite the added investment in land and labor and the delayed gratification in weed control savings. According to Brian Caldwell, who heads up field management and extension outreach for the project, the bio-extensive treatment returns over $16 for every hour of farm work. His calculations are based on fieldwork and harvest rates found in The Organic Farmer’s Business Handbook by Richard Wiswall and the Roxbury Farm website (https://www.roxburyfarm.com/). He used a land rent of $15 per 1/10 acre and Ithaca, NY farmers market prices: $1.25/lb for Delicata squash; .75¢/lb for cabbage; $2.00/head for bibb and red leaf lettuce; and .75¢/lb for Yukon gold potatoes.

At this stage in the experiment, the other three systems are more profitable than the bio-extensive treatment, providing a return in the neighborhood of $20/hour. If going bio-extensive under these circumstances reduces the return on labor, at least it does not necessarily limit the number of income producing acres in production. According to Brian’s analysis of how many acres each type of grower could manage working 1500 hours during the growing season, the bio-extensive market gardener could take care of 6.1 acres (including the fallow lands), almost double the acreage of the annual cropping systems (3.3 acres for System 2 and 3.5 acres for System 4.)

The not so good news from the OCS experiment is that dealing with a large seedbank of summer and winter weeds may significantly limit the soil building benefits of taking land out of production. Summer cover crops have been terminated earlier than optimal to prevent pigweed, lambsquarters and other warm season weeds from going to seed. Likewise, the winter cover crops of rye have been delayed, or turned under prematurely, in order to clean up the cool season chickweed.

Reduced cover crops biomass and increased tillage may explain why System 3 has not improved soil quality relative to the other three treatments. Annual soil testing under the direction of Laurie Drinkwater, current OCS Project Leader, indicates a lot of fluctuation in soil organic matter, active organic matter and soil aggregate stability over the first six years of the experiment, but no statistical difference between the four systems.

The unexpected benefit of routinely incorporating cover crops well in advance of planting the vegetables is that System 3 has avoided the nitrogen tie-up and soil moisture depletion which has reduced yields in the other treatments. For example, plowing down high biomass cover crops a few days before planting squash in System 1 (EP 1) and System 2 (EP 1 & 2) depressed yields and profitability. Squash production was much better in System 3 where the cover crop was shallowly rotovated at least four weeks before transplanting the Delicata. However, the cultivated fallow before squash planting did not reduce weed pressure.

Ironically, the results from the OCS experiment seem to suggest that the weed-the-soil aspects of System 3 have had more of a beneficial impact on yields than lowering the weed seedbank in the soil. Over the short term, the bio-extensive treatment might have generated more net income and better soil quality by letting go of the extra hand weeding in the cash crops, prioritizing soil building during the fallow year rather than weed seed depletion, and relying on a well designed rotation and mechanical cultivation to weed the crops and the soil as described in “OCS Insights on Ecological Weed Management.”

In conclusion, we must emphasize that it is way too early to draw any firm conclusions from this long-term research station experiment. The constraints of implementing each system in this setting are not only very different from real life farming, but another six years of data may tell a whole different story as the trends in weed pressure; soil quality and profitability become more apparent.

Differences between the four systems may also become more distinctive as the research team learns how to optimize each system. At the moment, the researchers and advisory committee are trying to solve the weak link in Systems 2 & 4 – how to establish a leguminous cover crop in fall cabbage that would provide enough nitrogen for the following crop of spring lettuce? The research team is also trying to determine why nutrient release and crop growth is sometimes delayed in the ridge-till system.

As farmer-consultants on the OCS project, we experimented this past year with using our single-row inter-seeding system and a variation on strip-tillage to address both of these challenges. The following photo essay documents each step of the adventure.

Low-Till Vetchtables

We first experimented with single-row inter-seedings of hairy vetch in the early 90s to prevent erosion in the valleys of hilled potatoes and to fix nitrogen during the establishment year of strawberries. Over the last few years, we have trialed this living mulch system for fall crops like these alternating rows of broccoli and lettuce. Four weeks after setting out the plants, we inter-seed the vetch into freshly cultivated soil using the walk-behind Planet Jr. set at the #24 seed hole.

Of all the brassicas, cabbage seems most compatible with the single-row inter-seeding of vetch. This observation made us think that this living mulch might have potential to grow enough nitrogen for a spring crop of lettuce in the OCS experiment. To test out the idea, we began an informal on-farm demonstration with the mix of fall crops pictured here in field 2 on September 14, 2009.

The following April, 2010, we lightly cultivated the bed middles to uproot the chopped brassica stalks, setback a smattering of winter weeds, and preserve soil moisture. We used the strip-till setup shown on the next page, then followed with the culti-packer and rotary hoe. “Row cropping” cover crops may seem like a contradiction in terms, but why wouldn’t the hairy vetch benefit from widely spaced rows and cultivation just like our vegetables?

Four weeks later and the row cropped vetch had completely filled in the field. Tilled in at this mid-May date, the inter-seeded legume would probably supply much of the nitrogen required by a spring crop of lettuce. Not bad for an investment of $36/acre ($1.20/lb organic vetch seed at an estimated seeding rate of 15 lbs/acre). But don’t forget the long-term investment in bio-extensive weed management necessary to make this inter-seeding system possible without a lot of hand weeding.

Curious to see the full potential of the row cropped living mulch, we decided to let it grow until the middle of June instead of planting spring lettuce. The sea of vetch more than doubled in size in a month’s time, increasing nitrogen and biomass production substantially. An added advantage of delaying incorporation is this overwintering legume is much easier to manage with minimum tillage when it reaches mid-bloom.

We did not realize how long and thick the single rows of vetch vines had grown until we tried to wade through the cover crop at high tide. Although you would not know it from the lush, green growth, 2010 started out unusually hot and dry. The row cropped legume had sucked the ground bone dry, spreading its nodulated roots throughout the 34” wide beds.

We knocked down the vetch vines with the custom built residue cutter shown in the Weed the Soil DVD and the “Peak Water” article in the Summer 2008 SFJ. With 500 lbs of added weight and a couple of overlapping passes, the residue cutter crimped the vines sufficiently to kill the vetch. Going over field 2 one more time after the dead mulch turned brittle…

…allowed the coulters on the residue cutter’s axle to slice the dense mat of vetch vines into 5-6” wide pieces.

We followed the residue cutter with the riding cultivator set up with a 12” wide sweep attached to an extra long shank and a heavy-duty cross bracket. We angled the sweep more aggressively than usual to loosen the planting zone in the middle of the beds and to…

…open up a furrow for incorporating compost without resorting to intensive tillage. We hand applied a one foot wide band of compost to five of the strip-tilled beds in field 2, including the inner two rows in this photo.

We used a double set of disc hillers to backfill the strip-tilled furrow with vetch residues and compost. This three-part seedbed procedure was very time consuming, but we wanted to see if mixing these farm produced soil amendments more deeply into the planting zone might point the way for earlier nutrient release and crop growth in the OSC ridge-till treatment.

By the last week of July, we had received just enough rain to recondition the strip-tilled beds and begin direct seeding salad mix, string beans, beets, daikon, arugula, turnips and spinach. Note how the miniature culti-packer trailing behind the cultivator draws sufficient moisture to the surface to germinate small vegetable seeds without irrigation.

We find it easier to cultivate strip-tilled vegetables in two steps. The first pass over the field we focus solely on light cultivation next to the row to preserve soil moisture. We use two pair of the small rolling units salvaged from our neighbor’s junked Lilliston cultivator.

We bolted the Lilliston rolling cultivators to 2” by 4” crosspieces so that the spyders run parallel to the row, the rear pair of Lillistons offset from the front pair like a rotary hoe. This crude zone cultivation setup makes it possible to thoroughly loosen the strip-tilled seedbed without burying this emerging row of salad mix with soil or residue.

The second pass with the cultivator we focused on loosening the packed pathways which has not been tilled or cultivated since inter-seeding the vetch in the fall vegetables over a year earlier. We used two pair of quack-digger teeth to rip up the firm soil, then immediately reseeded the loosened pathways to a single row of rye on August 28 with the Planet Jr. at hole #38.

This September 19 photo of the 2010 low-till vetchtables shows the second planting of spinach (seeded August 9) and inter-seeded rye getting established despite continued dry conditions. The two inner rows received compost in the strip-tilled furrows. Thanks to a good bit of rain the end of September and the nitrogen supplied by the inter-seeded vetch, all of the spinach produced abundantly over a six-week period. However, the composted rows were ready to harvest a full week earlier than the uncomposted spinach, suggesting that a band of compost incorporated into the planting zone may be an effective way to speed up early crop growth in a low-till system like the OSC continuous ridge-till treatment.

OCS Insights on Ecological Weed Management

One of the goals of the OCS project is to explore the relationship between soil management and weed pressure. For example, the vegetable experiment has demonstrated how a well designed rotation, in combination with timely mechanical cultivation, can maintain the weed seedbank at manageable levels. Although soil counts of pigweed seed rose dramatically after an early weed control failure for sweet corn in Entry Point 2, just two years later the pigweed seedbank had declined to one quarter of its peak density.

Chuck Mohler, the former OCS Project Director, attributes this self-correcting phenomenon to following sweet corn in the rotation with fall cabbage and spring lettuce – two relatively short term, easy-to-cultivate vegetables with very different planting windows. Few weeds have a chance to set seed during this two year period in the aftermath of the sweet corn crop. This seed shedding grace period also provides enough time for the majority of new weed seeds produced during the sweet corn crop to be flushed out of the soil through tillage and cultivation or to die-off from natural causes.

One of the natural causes that Chuck has been studying is the brief spike in soil pathogens caused by the incorporation of fresh cover crop residues in the soil. Follow-up greenhouse studies support his hypothesis that incorporating fresh plant matter reduces weed seed germination.

The OCS project also indicates that soil fertility management may influence weed competition. A satellite trial conducted at Klaus and Mary-Howell Martens’ organic grain farm tested this research question by applying different rates of chicken manure compost to all three crops in their rotation: corn, soybeans, winter spelt frost seeded with clover. Maximum crop yields were achieved at relatively low compost rates (substantially less than the compost rate expected to be needed for each crop). Weed size, on the other hand, continued to increase with each additional increment of compost applied, even at rates well above those that maximized yield of the grain crops. Small plow studies are in progress to determine which nutrients, at elevated levels, are responsible for enhancing the growth of pigweed and foxtail.

For more information on soil-weed relationships, and other OCS discoveries, go to http://www.hort.cornell.edu/extension/organic/ocs/.