Spring Growth – From the Ground Up: Soil Improvement

Summer 2010

Presentations at Spring Growth 2010

Eliot Coleman
At the Spring Growth Conference, Eliot Coleman talked about the importance of soil fertility and soil aeration in promoting the growth of pest-resistant crops. English photo.

The 2010 Spring Growth Conference at MOFGA’s Common Ground Education Center in Unity featured Dr. Will Brinton of Woods End Laboratories in Mt. Vernon, Maine; Eliot Coleman of Four Season Farm in Harborside, Maine; Dr. Sue Erich and Dr. Marianne Sarrantonio of the University of Maine; Dr. Fred Magdoff, co-author of Building Soil for Better Crops; and Dr. Eric Sideman, MOFGA’s organic crop specialist.

Fred Magdoff: Principles and Practices of Ecological Management of Soil

Fred Magdoff is professor emeritus at the University of Vermont; directed the Northeast Sustainable Agriculture Research and Education (SARE) program for 20 years; and co-authored Building Soils for Better Crops, which is available in print and as a free download from SARE.org.

Magdoff began with a quote from Vandana Shiva’s book Soil Not Oil: “It is our work within the soil that provides sustainable alternatives for the triple crises of hunger, energy and food. No matter how many songs on your iPod, cars in your garage, or books on your shelves, it is plants‘ ability to capture solar energy that is the root of it all. Without fertile soil, what is life?”

Soil is the under-appreciated natural resource, said Magdoff; the basis of life.

Magdoff said that a healthy soil has:

sufficient nutrients for plants but not excess nutrients that can pollute or cause problems with plants or groundwater or surface water. Too much nitrogen (N) in plants relative to other nutrients makes them more susceptible to insects.

good tilth, or soil structure – how soil particles stick together

sufficient depth; it is very difficult to deal with soils that are shallow to bedrock, except on a small garden scale

good water storage and drainage, which is related to soil structure. The better the soil structure, the more water can enter and be held in the soil, available for plants, and excess can drain from the soil.

no chemicals that might harm plants, such as soluble aluminum (Al) at low pH (one of the reasons we lime acid soils); and no harmful human-made compounds. Magdoff noted that Al is present in all soils but is a problem only at low pH levels, where it is soluble.

Sue Erich, Marianne Sarrantonio and Fred Magdoff
Sue Erich (standing, end of table), Marianne Sarrantonio (sitting) and Fred Magdoff (sitting) answered questions about soil fertility. English photo.

low populations of plant disease and parasitic organisms

high populations of organisms that promote plant growth

low weed pressure. Biologically active soils tend to suppress weeds as insects eat weed seeds, fungi destroy weed seeds, etc.

resistance to degradation. You can degrade any soil if you work hard enough, said Magdoff; but you should have to work harder to degrade a healthy soil.

resilience – the soil can bounce back from damage.

The physical, biological and chemical properties of soils interact with each other, and soils should be managed with all three in mind, said Magdoff.

Soil organic matter (OM or SOM) and its management are at the heart of soil health. This organic matter includes:

the living – plant roots, nematodes (most are beneficial; very few are parasites or will inject disease organisms into plants; most are eating other nematodes, bacteria or other organisms and are not harming plants), fungi and bacteria (most of which are also beneficial), earthworms, springtails, moles, mites, etc. Keeping large populations of these enables them to control one another, providing a system of checks and balances. Soils with less OM tend to have fewer species of organisms and tend to favor those that feed on the OM presented to them. As SOM decreases, plant roots make up a greater percentage of the remaining OM, so you’re selecting for organisms that feed on plant roots; hence, plant disease and nematode problems increase. Most plants are infected with mycorrhizal fungi, which act like root hairs by greatly expanding the volume of soil from which plants can draw nutrients – especially phosphorus (P). Mycorrhizae, in return, get photosynthates from the plants. Soils tend to have more mycorrhizal spores after a cover crop, because the mycorrhizal fungi can associate with the living cover crop and produce spores. When subsequent crops are grown for market, they tend to host more mycorrhizae. These high infection rates also help protect the crops against diseases and nematodes.

the dead – recently dead soil organisms and recent crop residues. These provide food (energy and nutrients) for soil organisms. This fraction is also called the “active” or “particulate” OM. It includes sand- to silt-sized particles that are small but can still be seen with the naked eye.

the very dead – well decomposed OM, also called humus. This fraction contains high amounts of negative charge (cation exchange capacity, or CEC), which allows it to hold some nutrients. Magdoff reserves the term “humus” for this fraction. “I presume biochar belongs here,” he said.

Organic matter makes up 1 to 6 percent of most soils on a weight basis. Sandy soils normally have about 1 percent OM; clayey may have 5 or 6 percent; loamy, about 3 percent. These figures can be higher or lower. Prairie soils when they were first plowed could have been 50 percent OM. Generally, some 10 to 20 percent of SOM is living; 10 to 20 percent, dead; and 60 to 80 percent, very dead.

How can such a small part of the soil be so important? Madoff explained that OM influences all soil properties except texture, either changing them or influencing how they are expressed. (Soil texture by definition excludes OM and is simply the percent of sand, silt and clay in the soil.) Organic matter:

influences nutrient availability by supporting mycorrhizal fungi, for example, and P-solubilizing bacteria. As OM decomposes, nutrients are converted into forms that plants can use. The cation exchange capacity (CEC) of OM enables it to hold positively charged ions such as calcium (Ca), magnesium (Mg) and potassium (K) against the force of water leaching through the soil.

provides the sticky substances that hold sand, silt and clay particles together, promoting soil aggregation, which promotes water infiltration and drainage

promotes water storage and availability. In dry years, this is especially apparent in soils and in plants. Soils with more OM are softer and easier to work; those with less OM are harder.

promotes diversity and activity of soil organisms. By adding OM to the soil, you’re feeding these organisms; and adding a diversity of OM types feeds a diversity of organisms.

makes soil darker, especially in sandy soils. In the Midwest, color charts can be related to SOM, with darker brown correlating with greater OM. This doesn’t work for the clay soils in Vermont’s Champlain Valley but does work in some other soils.

enables soil microorganisms to produce growth stimulating compounds such as plant hormones or chemicals that behave as plant hormones that stimulate root growth, root division and other plant processes. Soils with more OM have more of these microorganisms and their plant stimulating products.

Despite all the benefits of OM, soil degradation is a major problem worldwide, and the decrease in OM is part of this degradation. Degradation follows this pattern: Intensive tillage, soil erosion and insufficient added residues lead to aggregate break down, which leads to decreases in soil OM. More erosion follows, the soil surface becomes compacted, and less water enters the soil. This downward spiral continues – but we want to go the other way to produce healthy soils.

The Cornell Soil Health Test is the only soil test Magdoff knows of that analyzes chemical, biological and physical factors of soil to help farmers make decisions about their cultural practices. (See “How Healthy is Your Soil?” The MOF&G, March-May 2009; http://mofga.org/Publications/MaineOrganicFarmerGardener/Spring2009/HealthySoil/tabid/1079/Default.aspx) Magdoff showed a soil from an organic farm and from a conventional farm subjected to a simulated rainstorm as part of Cornell’s Soil Health Test. About 70 percent of soil from the organic farm consisted of water stable aggregates, while most of the soil from the conventional farm was broken down by the rain into small particles that went through the sieve on which it was placed, with only about 20 percent remaining. A well aggregated soil has improved water infiltration and storage capacity; a poorly aggregated soil will generally crust over and be subject to runoff and erosion.

The Cornell test also looks at the root health of beans growing in each soil. In good soils, roots are more extensive and have a healthier color.

Magdoff said that adding OM increases biological activity and diversity and reduces soilborne diseases and parasitic nematodes, leading to healthy plants. As OM decomposes, sticky compounds are produced which promote soil aggregation, and that improves pore structure, soil tilth and water storage capacity. Also, humus and other growth promoting substances are formed; nutrients are released; and harmful substances can be detoxified.

Organic matter is also an important part of regional and global cycles of carbon (C), N and water. The amount of C on a dry weight basis in the top 6 inches of a soil with 1 percent OM is the same as all the CO2 above the field. About three times more C is stored in soils worldwide than in the atmosphere.

Overall, ecologically based agriculture follows three strategies, said Magdoff:

Create conditions above and below ground that produce healthy plants that have enhanced capabilities to defend themselves, and/or

do things that stress pests, and/or

do things that enhance beneficials.

Growers should be doing one or more of these. Some, such as cover crops, do all three: stress weeds; enhance beneficial insects when they flower and provide places for mycorrhizal spores to germinate; and improve soil structure, which helps subsequent crops.

Plant defend themselves against pests in several ways. Magdoff noted three mechanisms that occur after insects feed on plants.

When insects start feeding, plants produce chemicals that slow pest feeding but don’t kill the insects. These chemicals are not produced at other times.

Plants give off volatile compounds that attract specific beneficials that attack pests, such as specific beneficial wasps that attack specific caterpillars. Magdoff noted a Scientific American article about a wasp that lays eggs in tomato hornworm caterpillars, simultaneously injecting a virus that deactivates the caterpillar’s immune system. If the virus isn’t injected, the caterpillar defeats the eggs that are trying to develop in it.

At the sites of feeding wounds, plants increase their extrafloral nectar flow, which provides food for adult beneficial insects. Magdoff noted that plants can be giving off all these signals and nectar, but without sufficient habitat, the beneficials won’t be there.

Magdoff described two soil-related ways in which plants defend themselves against diseases:

Systemic acquired resistance (SAR). When some disease organisms begin to interact with plant roots, feeding on them, for example, the plants produce salicylic acid, which induces the plant to produce proteins that defend it against those particular diseases.

Induced Systemic Resistance (ISR). Plant growth promoting rhizobacteria (PGPR) that live near plant roots stimulate plant roots to produce ethylene gas, which provides resistance to a number of plant pathogens.

“I like to visualize a growing season from an ecological point of view in three stages,” said Magdoff.

Build internal strengths into agricultural ecosystems, above and below ground. Develop habitat in the field and in soils to support healthy plants, to stress pests and enhance beneficials.

Use routine ecologically sound practices during the season to keep plants healthy: Scout for pests and take care of them in an ecologically sound way; irrigate during droughts.

Practice reactive management. When organisms get out of control, you have to do something. This is the last line of defense in organic management but the first in conventional. “They think in terms of reactions,” said Magdoff. “From an ecological point of view, we want to think in terms of prevention.”

Above-ground and below-ground practices can make farms more ecological. Magdoff focused below ground – i.e., how to build healthy soils.

Add plentiful amounts of OM from crop residues (including cover crops) as well as off-field OM, such as manures and compost. For example, corn grown for silage leaves hardly any above-ground residues; corn grown for grain leaves about 4 T/A of above-ground residues that the soil can use; so the latter practice is better. Different organisms have different “taste” preferences and do different things in soils (such as building soil structure, breaking down OM, etc.), so supply various kinds of OM.

Keep soils covered with living vegetation and/or crop residue as much as possible. Rotate with hay or pasture crops. Use cover crops or perennial sod. Reduce tillage. This supplies food and habitat for maintaining biodiversity; suppresses insect, disease and weed cycles; helps grow healthier plants through better soil tilth; improves nutrient- and water-holding capacity, and more. As examples, Madoff showed photos of a winter rye cover crop; and of a rye/hairy vetch crop in which strips were mowed in the spring, and tomatoes were planted in the mowed strips. After the tomatoes were staked, the remaining vetch and rye was mowed to provide mulch. Another system uses a forage radish (Raphanus sativus var. niger) with a large taproot – ”biodrilling” according to grower Steve Groff – which winter kills, helps with water infiltration, breaks up compacted layers, and seems to suppress weeds.

Use better crop rotations. Most growers say they can’t afford four years of a grass/legume pasture and one year of vegetables or some other crop; Steve Groff of Cedar Meadow Farm in New Jersey says he can’t afford not to do this. Vegetable growers can cooperate with dairy farmers to do this.

Reduce tillage intensity. The purpose of intensive tillage is to destroy soil structure in order to create a fine seedbed. If you do practice intensive tilling, then rotating into a sod crop is even more important. Better machinery helps, including better planters and a roller-crimper to kill cover crops. The roller-crimper won’t kill a sod-type crop, but it will tremendously suppress a cover crop.

Use other practices that reduce runoff and erosion, such as growing permanent grass in areas subject to erosion.
Reduce soil compaction so that plants are healthier and less attractive to pests and/or better able to defend themselves. An experiment at Cornell showed that flea beetles are attracted to cabbage growing in compacted soil but not to cabbage right next to them in uncompacted soil. Don’t travel on wet soils; the wetter the soil, the deeper the compaction will go if you do travel on it. Use controlled traffic lanes that run on either side of permanent beds, raised or not, and distribute loads better. Increase organic matter. You can compact high OM soil, but you have to work harder to do it.

Use best management techniques to supply nutrients without degrading the environment. Get nutrients to plants when they need them. If you’re using OM to supply nutrients, this happens naturally: As the soil warms, OM is mineralized, i.e., nutrients are released, just as plants are starting to grow. Importing too much compost or manure can lead to too much N or P – something that has happened on some organic farms. Don’t rely on imported compost or manure forever as your main source of OM and nutrients; instead, grow your own OM and recycle nutrients on your own farm.

The key is to use multiple tactics, including the seven above. Using just no-till farming is not enough; you need good rotations, reduced compaction, and so on.

Is old, composted bark OK to add to soil?

Magdoff: Fresh wood can tie up nitrogen. If it’s well decomposed, it probably has N in it and is OK to use. It may not provide much N but will not tie up N either. Be careful about how much you apply.

Does it make sense to buy humates to add to the soil?

Magdoff: If you have a reasonable amount of OM, there’s no need to buy humates. Humates occur naturally in soils. “I’m skeptical of things that are sold that you have to add to your soil, because you can do it on your own.

Is it possible to add too much compost or OM?

Magdoff: You can overdo it with respect to nutrients, especially P; and it’s possible to have nitrate leaching and salt injury from too much nitrate. Research at UConn found a number of organic farms had excess soil P. When the prairie soils were first plowed, they didn’t need N fertilizers for years – but they were leaching N down the rivers, as they are now (from synthetic fertilizers).

Soil Management Panel

A panel featuring Dr. Sue Erich (SE, below) and Dr. Marianne Sarrantonio (MS) from the University of Maine, Dr. Fred Magdoff (FM), and Dr. Eric Sideman ES) from MOFGA answered questions from Spring Growth participants.

Soil pH

Q: How important is soil pH for growing crops in Maine?

MS: It’s extremely important. Maine has some acidic clay soils where things grow but not so well. I have to lime my garden every year. It’s a constant struggle in Maine to keep the pH above 6, which is where we need it for most crop plants. The native flora, such as blueberries, is adapted to low pH soils, but our crop plants aren’t. Compost can raise or lower the pH, depending on the materials used.

SE: Soluble Al is the biggest problem with low pH soils, because it damages plants roots, so your plants are stressed right from the beginning. Wood ash is a good liming material that a lot of Maine people can access. If you apply wood ash regularly, you may not need more than that. Wood ash varies in composition depending on how hot your wood stove burns, what type of wood you’re using… Typically wood ashes have high liming ability. They can be tested to see exactly how they compare with lime. They do change the soil pH fairly rapidly and provide additional nutrients, such as K and a little P.

FM: Their liming ability is about 60 to 80 percent of that of limestone

ES: When you’re starting with a new plot, pH is the first thing to address. Some nutrients may be of limited availability because the pH is low. Add lime, raise the pH to 6, then test the soil again to see which nutrients are still low.

FM: Acidification is a natural, ongoing process. Once you get the pH up, it won’t stay there – but the more OM you have in the soil, the more slowly the pH will go down again.

Q: How low does the pH have to be to cause Al toxicity?

SE: If it’s less than 6, and certainly below 5.5, you begin to see soluble Al. With anything less than 5.5, plant roots will be dealing with soluble Al.

FM: The lower the pH, the more soluble Al you will have. The more OM, the more protection you have. A colleague was able to grow barley in a soil with a pH of 4 but a lot of OM, and barley is very sensitive to Al toxicity.

Q: Some horse manure compost tested at pH 7 and Al was high.

SE: Probably some soil was in the compost, and total Al was high, not soluble Al. Insoluble Al in soil is not a problem for plants.

Q: I read years ago that all compost ends up at pH 7, regardless of the initial ingredients.
MS: Mature compost has a pH of 7. It can get over-mature and have a different pH, so using compost at the right stage of maturity is important.

SE: It depends somewhat on what you start with. Some animal manure has a high pH.

FM: If you’re using compost for disease suppression, that is apparently lost as compost ages, so you want mature but not aged compost.

Q: What are the hazards of using too much wood ash in a home garden?

SE: Some wood species, such as birch, accumulate cadmium, but it’s unlikely that anyone would burn exclusively birch and end up with too much cadmium. More of a concern is throwing the lime on the garden without checking the pH; over-liming up to pH 7 or so will cause problems with nutrient availability. Ashes aren’t especially high in P (1 or 2 percent), so that should not be much of a problem. Be sure to keep checking the pH, even with a home test kit.

FM: When we were working with wood ash from an electrical generating plant, over-liming was a real problem – but it was harder to get a reduction in plant growth with wood ash than with straight limestone, probably because wood ashes have K and other nutrients that you don’t get with limestone.

Q: Wood ash doesn’t have much magnesium (Mg), so if soils are low in Mg you can have an imbalance.

SE: And wood ashes have K, which can affect Mg uptake.

Q: I’m working with a soil with a pH of about 4.8 that has a lot of wood chip matter in it. I limed it, and some reacted in a year, some didn’t. Did the wood chips affect the pH?

SE: OM in soil does buffer against pH changes. That buffering can work with you and against you. You will have to add more lime than you would add to a soil with less OM in it. Once the soil pH is up to 5.5 or 6.0, it will resist the natural process of acidification.

FM: The soil may have had more OM where you didn’t see much of a change. How did you mix the lime in? I’m a proponent of not beating up the soil, but lime works faster if you incorporate it.

SE: The limits we put on the amount of lime to apply in a year are mostly economic. It’s too expensive for most farmers to add a lot of lime in one year.

Mycorrhizae, Beneficial Nematodes

Q: Do mycorrhizae live in the soil over winter?

MS: They do form spores and can live in the soil, but if you want them to live and propagate, they need living roots in the soil almost all the time. I did some work with them, and we found that they proliferated on perennials but not much on annuals. It takes them a long time to establish their hyphae on annuals. So the longer a crop is in the soil, the better.

FM: This is one of the reasons to have cover crops. Otherwise you only have the spores overwinter, and some of these die.

Q: Is there any point in inoculating soil with mycorrhizae?

FM: I’m not aware of any evidence. (Magdoff added later that mycorrhizae that form relationships with trees are of a different type. “It certainly makes sense to me to inoculate trees, perhaps best done when transplanting.”)

Q: Do brassicas kill mycorrhizae?

FM: I don’t think they kill them, but mycorrhizae don’t form associations with them.

Q: To encourage mycorrhizae, are any cover crops OK or are they host specific?

MS: They are host-specific. Brassicas don’t host them at all. Legumes seem to have higher infections, and a mixture of grasses and legumes would give you different types of mycorrhizae. I’m not sure, if you want a particular type of mycorrhizae, how you would get it – and I’m not sure it matters that much which species of mycorrhizae you have. I think the important thing is to have them there.

Q: If I use beneficial nematodes – an exotic species – to control cutworms, will this upset the diversity or ecological balance in the soil?

FM: I don’t know.

Organic Matter and Cover Crops

Q: Sir E. John Russell wrote that once you reach 15 percent OM, the particles you started with are immaterial; you had overcome the type of soil (i.e., soil texture) you started with.

FM: The definition of soil texture is how much sand, silt and clay is in it. That’s determined by destroying the OM and then doing a particle size analysis. So you can’t change the texture of soil, unless you bring in other minerals. You can change a clay soil into a loam, i.e., change its texture, by bringing in an incredible amount of sand. Bringing in OM doesn’t change the texture, but it changes the way that texture is expressed.

Q: What are your favorite cover crops?

ES: There is no best cover crop. You have to know what benefit you’re looking for, and then choose the cover crop that supplies those benefits.

MS: I used to be a big proponent of hairy vetch, but it only overwinters about one of every two years in Maine. Cereal rye is about the only thing that will reliably overwinter in my part of Maine (Orono). Those farther south have more choices. If you’re looking for soil protection and not necessarily N fixation, a mix of oats and field peas is nice; it will winter kill. Give the cover crops a chance to grow. If possible, take part of your land out of production for a year and put in a perennial cover crop. The benefit you get will probably outweigh the loss of that land to crop production.

Q: Buckwheat and field peas (from Fedco) together, as a cover crop, works great for me. They’re sown at the end of May. Buckwheat cools the soil, which the peas like. The peas grow up the buckwheat. They flower together and bring in the bees. They’re tilled in in late June or early July, then I plant late broccoli, cabbage in mid-July on. Then in the fall I sow oats and peas.

Q: In managing cover crops, is there a difference between mowing them every few weeks or grazing them, versus letting them grow until they flower?

MS: You get more total biomass if they’re mowed and allowed to regrow. If animals graze, you get the manure, but the animal gets a lot of the biomass too, so that changes the game entirely. Mowing once is what I usually do. Once the seed head of annuals starts to form, you don’t want to mow it and expect it to grow back, for the most part. Most of the cereals respond well to mowing; vetch does not; annual clovers do. It’s specific to the crop, but the short answer is yes, you’ll probably get more total biomass if you cut the cover crop once.

ES: The numbers I’ve seen concerning feeding cover crops to livestock is that 50 percent of the OM and 75 percent of the minerals, roughly, are returned to the soil in manures. The problem is the redistribution. My sheep will graze all over a cover crop but they put all their manure under my trees in one corner.

Q: Is tillage bad if you’re adding OM as you till? How many tons per acre of OM do you need to add to overcome the disadvantages of tilling?

FM: You’re not just losing OM with tillage; you’re also breaking down aggregates, which enhances OM decomposition. But you can replace the accelerated OM that’s been lost. An experiment I inherited when I came to Vermont addressed this. To keep the OM content the same in continuous, tilled silage corn after 10 to 12 years or so when adding very few residues, you needed to add the equivalent of one to one and one-half cows’ worth of manure or about 20 T/A. That’s a big Holstein type cow. If you are doing intensive tillage, you need to be doing other things – adding specific residues, growing specific crops …

Q: How do you come out of three or four years of sod and create a fine seedbed?

FM: You need tillage, especially for fine-seeded crops. But do you really have to till the whole field? Can you do zone tillage? Can you have permanent beds or zones that don’t get tilled?

Soil Testing

Q: Is the Cornell Soil Health Assessment worth its cost?

MS: The Natural Resources Conservation Service (NRCS) has a kit that’s cheaper and is a little more workable on the farm, and you can buy a subset of it; but Cornell does some things that NRCS doesn’t.

FM: The Cornell test is the only soil health test available. I’m pretty impressed with it. [The basic package costs $40; the comprehensive package, $65.] A traditional soil test looks at pH, lime requirement, K and other nutrients. The Cornell test assesses common diseases, physical properties, aggregate stability and more. They have lots of data from lots of farms, so they can fit your data in with them and make suggestions about what to do. You probably won’t want to do the Cornell test every year, but it’s worth the cost from time to time, especially if you have a problem field.

Other Questions

Q: What can you do about lower areas at the base of slopes that flood in wet years?

FM: Try raised beds and/or, if possible, drainage ditches.

MS: You’re probably getting more nutrient leaching on the drier hillside above the low area than at the bottom, because water’s not moving through [at the bottom]. Building up OM will help by increasing cation exchange capacity. If N has turned into nitrate (NO3) before it drained, it will probably leach; but in the saturated soil, it won’t turn into NO3 because there’s no oxygen.

ES: Make a fall-prepared raised bed covered with plastic so that you can get onto the field in spring. That will stay drier and you won’t have to walk on the area.

Q: What are your recommendations for hedgerows or traffic alleyway crops that would also inoculate the soil with beneficials?

FM: In traffic zones, don’t expect plants to flower and attract beneficial insects; the traffic will suppress those plants. To attract beneficials, you need plants that flower at different times.

Q: There are roughly 500 to 1,000 acres of vegetable crops represented in this room and probably 10 times that in open land management. Most fields in New England are acidic and low in fertility. How do you bring soils up to what’s needed to grow crops?

FM: Apply lime or wood ashes in appropriate amounts. You could need up to 6 or 8 T/A of limestone, which can get expensive. Start doing it gradually. Lime reacts much more quickly if you incorporate it, but if you’re using fields for pasture, try to improve the pasture by frost seeding legumes and adding some lime; some will work its way in. Brush hog old fields and get some animals on them and let them help you.

Q: How do you reduce the risk of late blight overwintering in the soil?

ES: It only overwinters in living tissue, such as potato tubers. Look for volunteers and cull piles and destroy them.

Q: Can you comment on the growing trend toward producing nutrient dense crops?

FM: The idea is to import nutrients to get your soils just right, and that will produce nutrient-dense plants. I haven’t seen evidence (e.g., replicated experiments) that finely balancing nutrients in the soil does anything.

Q: Is there a correlation between higher levels of OM and higher levels of nutrients in crops that are harvested from those soils?

FM: Organically managed plants have fewer problems. This has been established again and again. There is something in the plant that is turned off or enhanced. In a greenhouse study, the European corn borer preferred to lay eggs on conventional corn. So something is going on there.

MS: When adding OM, we don’t have to think about micronutrients. They’re there. When working with organic fertilizers applied at the same N rate, the more complete fertilizer that came from the whole plant or animal versus blood meal, which comes from part of the animal – yields are higher with the whole material. This is anecdotal now. It may be due to micronutrients.

Good soil
“A vibrant, healthy soil takes years to achieve,” said Will Brinton at the Spring Growth Conference, showing this soil with good crumb structure as an example. Photo courtesy of Will Brinton, Woods End Lab.

Will Brinton: Managing Composts for Soil Microbial Activity

Will Brinton has studied compost for more than 30 years and owns Woods End Laboratory in Mt. Vernon, Maine, which researches and consults on compost quality worldwide.

Brinton said that people think of compost as an end product, but compost is a process and is good to balance some properties of some waste materials that, by themselves, would harm soil. The Benzinger Family Vineyard in California, for instance, had a wine cake pomace with a pH below 5.0. “You put that on your soil and nothing grows, basically,” said Brinton. But combining it 1:1 with cow manure with a high ammonia concentration and a pH above 8.0 – a material that, applied alone, would also be harsh on the soil and could burn plants – makes excellent compost after about three months, Brinton found, with a balanced analysis of 2.2-1.7-2.8, 43 percent OM and a pH of 7.2.

“My interest in composting is to use it to balance unusual and extreme ingredients,” said Brinton, “such as potato culls that get dumped along fields in northern Maine or Canada; such as fish waste that by itself is very harsh and odorous. At Woods End we’ve advocated compost because it could correct some of these materials so nicely and make them very useful for application.”

Organic matter decay drives the soil OM-microbe-nutrient cycle, said Brinton. He showed a magnified photo of a piece of decaying straw with humus forming on it as microbes were eating the straw. “Humus is being formed chemically during the decay. That’s what’s so remarkable about composting: It’s converting raw OM into humus, which radiocarbon studies show lasts in soils as long as 2,000 years.” So it’s putting C into the soil in an active form. “Humus forms an aggregate that has actual soil minerals as part of it, and pieces of undecayed matter all together in what we call an aggregate, and it holds it in the soil over a period of time.”

Pomace and manure
Farm manure was mixed with pomace left over from wine production in California to make quality compost. Photo courtesy of Will Brinton, Woods End Lab.

The Reality of Soil and Compost

At 3 percent OM, an acre slice of soil (an acre of soil 6 inches deep, about 1,000 tons of soil at 1.3 g/cc bulk density) contains 30 T/A of organic residue. The microbial count in that soil may be 106 to 109 per g of soil, which sounds huge, said Brinton, but its biomass is a “surprisingly small” 1,000 ppm or 0.1 percent of the total weight of the soil.

“Some people say that’s small enough to be ignored,” said Brinton, “and I think conventional farming has actually taken that number and ignored it because it is so small. But that 0.1 percent does a lot of things in the soil. But when you talk about substantially affecting the soil with microbes and humus, be very, very careful, because the numbers are very, very tiny, and you can get yourselves into a corner on this because you can make it sound like you’re having a huge impact on the soil when, in fact, it’s relatively small.”

While soil may have about 3 percent OM, compost may have about 30 percent OM, so a wet ton of compost with a bulk density of 0.3 g/cc contains 300 pounds of organic residue that is 50 percent water. The microbial count may be 106 to 1012 per g, “so we tend to say that compost is richer in microbes than soil, but the density of compost is about one-fifth that of soil, so the biomass or microbial mass of compost is the same as or less than that of soil under normal conditions. So it’s like putting soil on soil,” said Brinton. “In the popular literature we’re all saying we’re adding microbes when we put on compost. You’re actually adding microbial populations at about the same [level] as what’s already in soil.

“I’ve gotten myself into interesting research about microbial diversity, and you can get into some serious arguments about this based on claims that we are substantially altering soil microbial biomass. So I thought, this is an area we should actually go into and find out, scientifically and quantitatively, what is actually going on when you provide this mass of material to the soil, but the microbial numbers are so similar to the background that you’re already applying it to.”

A vibrant, healthy soil takes many years to form, Brinton continued, because you’re developing an open crumb structure. He showed a picture of such a soil with relatively low bulk density because it’s enriched with roots and decaying OM, earthworm canals, porosity and aggregates, and it has a high percentage of retained nutrients that are not necessarily immediately available. “This kind of soil takes a long time to achieve,” he said. “It’s not something that overnight you put on the compost and suddenly you have dark gray soil.”

Soil OM includes humus, roots and microbes. The humus is not living; it’s polymers of OM. But the microbial components are associated with the humus, surrounding it and feeding on it constantly. The other living component of soil is roots. Brinton showed a closeup photo of a soil with a root growing through it. “You can see all the different colorations of the soil, which is the humus soaking into the mineral matter, and plant roots are coming through that mass. One of the most interesting things that has come out of these long-term studies on soil OM management is how much you can sustain the humus in soil just by diligent care of crop residues.”

At some agronomy meetings in 2009, Brinton listened to researchers from the 200-year-long Rothamsted Long Term Plot Studies in England, where some plots were fertilized only with chemicals, some only with animal manures, some with no fertilizers, and some with just crop rotations and no fertilizer. They found that crops and root residues can sustainably contribute 1 T/A/year of OM to the soil just through crop management. They showed examples where that is sufficient OM to keep the humus from ever being depleted, said Brinton. “That’s why you can go to a farm in Germany now that’s been farmed continuously for 1,000 years, and the humus content is still where it was when they started testing soils, about 180 years ago. The steady state microbial biomass of these soils is about 1 T/A or 3 percent of OM.”

So managing OM is not just about dumping compost on soil, Brinton continued. Pay attention to the root material left after harvest; use care to return to soil plant matter you have not harvested. “This is why there’s so much concern about biofuels: If we start robbing our soils of all the fibrous material that’s detritus, not putting it back in the soil but turning it into biofuel, we’re going to lose that 1 T/A component or at least a major fraction of it, so our soil sustainability will decline.”

Applying Compost to Soil: Microbes Perish

Applying 10 T/A of compost, with 50 percent water, and 40 percent OM in the dry matter, to the soil means applying 2 T/A of raw OM – twice what the crop residue might have been. “So you can have doubled the contribution with that relatively small addition. Of that addition, microbial biomass may be only about 25 pounds of living microbes. When you take 25 pounds and spread it over an acre, you couldn’t even measure it. It’s really a drop in the bucket,” said Brinton. “It almost defies logic, because the quantity is so tiny. When we talk about feeding the soil with compost, you could hold those 25 pounds of microbes in two hands. You have to be careful what you imagine that 25 pounds of microbes is capable of doing to soil.”

Brinton showed typical field application rates of compost and what they may provide (in pounds):

Average application rate of compost10 T/A20 T/A50 T/A
OM (dry)4,000 lbs.8,00020,000
N, P, K, Ca, Mg5001,0002,500
Microbial mass*2550125

*Assuming 3 percent of dry OM is microbial mass

He noted that putting 40 T of compost on an acre will add 1 T of minerals. “That’s a lot of minerals.”

Applying 50 T/A of compost adds 20,000 pounds of OM and only 125 pounds of microbes. “I’m not trying to diminish the microbial picture,” said Brinton. “I’m trying to put it into context. The numbers may vary a lot.”

So what can we expect from compost? Brinton asked. When we apply compost to the soil, it will degrade slowly over the next three to four years – usually more rapidly at first, then at a diminishing rate. The remaining, tiny fraction can continue to decay very slowly over 2,000 years.

Depending on the maturity of the compost, less than 25 percent of the total N and most of the P and K will be available in the first year. “This is sometimes a disappointment to people, that they don’t get all the N out of it that they want for a particular crop.” Brinton has done replicated field plot studies with composts available in Maine. In one study, only 9 percent of the N went into the system; in another, 11 percent. “You really have to not overestimate the amount of N going in, but the question is, what happened to the rest of it?” That becomes an interesting discussion, said Brinton.

The microbial content of the applied compost is likely to perish in the soil. Brinton thinks those microbes become “food” for well adapted, indigenous soil microbes. “The idea that you can take a compost that has a certain spectrum of microbes and introduce it to the soil and affect the population dynamics of the soil, to me is completely unprovable. What we are able to show is that the microbial content stimulates the indigenous soil bacteria, which thereby reproduce themselves and grow at an increased rate. A hallmark of quality soil is a well developed, adapted microbial population that is not easily influenced by outside effects – and that’s a good thing.”

Disease Suppression from Compost

Brinton then addressed using compost to suppress diseases. In the early ‘80s, significant antifungal effects of compost were reported, particularly when an extract was sprayed on plants. (1980-1998, Univ. of Bonn, Germany; H.C. Weltzien et al.)

“This is where the whole compost tea movement comes from. It then became a whole, other thing in this country as compared to what was going on in Europe,” said Brinton, who knew Weltzien personally and worked with one of his students, Andreas Tränkner, who took over his department. Brinton showed a photo of grape plants in which controls were suffering from powdery mildew. The only treatment the other grapes received was compost tea sprayed on the plants and put around the roots as a topdressing. The surfaces of the leaves of treated plants were colonized by compost bacteria. “The leaf was so covered with these beneficial microbes that when fungal spores landed on them and tried to germinate and grow into the leaves and cause disease, they were being outcompeted by these indigenous organisms.” This prompted a new field in Europe: studying the biosphere of the leaf and the microbial population that lives on the surface of a plant.

Later studies – some from Ohio State by C. Potera – showed indirect systemic effects: Composts put compounds into the soil that plants took up internally and these promoted natural disease resistance.

However, the effects of these suppressivity studies have not been consistently reproducible. “You can do a study one year and get great results, and do the same study next year, and there’s no resistance or fungal suppression, and that makes it look bad to the industry of growers who say, ‘You need to give us a consistent product that does this again and again and again.’ That’s why chemical fungicides sell so well.”

After 30 years of reports of disease suppression, no real industry has come out of it. “There is no product you can buy that does it consistently. It’s left to the grower to innovate their own methods,” said Brinton.

Something exciting from Germany, said Brinton, is the use of compost microbes to improve the hygiene of crops indirectly. One replicated study involved spreading compost in the fall under grape vines, after leaf fall. The compost increased the litter decomposition rate by 25 percent and reduced spring ascospore germination by about 90 percent, and so reduced mildew spread from those leaves.

“That’s an amazing effect of just a surface spread layer of compost,” said Brinton. “It’s a purely physical/microbial thing that’s going on, where it’s helping break down the litter so that the fungal-inducing spores do not have a chance to germinate and affect the plants the next year. This is the kind of work that would be very useful in New England, where we do have so many injuries of mildew, particularly on fruit – to have a compost management practice the fall before that helps increase the decomposition of surface-borne spores that cause disease at a later time.” (“Compost Practices for Control of Grape Powdery Mildew (Uncinula necator),” Tränkner, Andreas and Brinton, William, 1996, www.woodsend.org/pdf-files/will2.pdf)

Another exciting area concerns root stimulating bacteria. Brinton showed slides from his work of plants growing in a medium supplied with chemical fertilizers and others supplied with the same amounts of nutrients as compost. “We had significant increases in root mass, rooting depth and the amount of roots. The differences in root surface area under these organic systems were enormous, compared to the plants that had ample amounts of nutrients and therefore didn’t put out much root mass in order to get it. You could almost say the plants on the left [with chemical fertilizers] felt they didn’t need any roots because they’re awash with chemicals. You could have different theories about it. But the plants [with compost] were able to extract nutrients from the deep soil profile, as well as withstand drought. These are some of the important indirect effects.”

Internet searches for “root stimulating bacteria” or “plant growth substances from microorganisms” bring up a body of science. “We don’t even know what these chemicals are,” said Brinton, “and it’s difficult to isolate and quantify the sources of these effects, but they’re associated with decaying OM.” (Brinton, M.S. thesis, 1980, “Effects of Composted and Uncomposted Manures on Corn, Wheat and Soybean Growth and Development,” Susan B. Anthony University, St. Louis)

Summarizing the microbial effects of compost, Brinton said that the direct microbial impact of compost on soil is actually much less than believed; that the microbial diversity impact of compost has never been proven. The silver lining to that, he said, is that soil microbe populations are extremely adapted and stable. More and more microbial ecology studies show that microbial populations in soil often have to do with the geologic origin of the soil. “These are microbes that have learned to live in that environment over hundreds if not thousands of years. Many of them have not been classified, because they’re not medically important microbes; so we can note that they’re there, but we don’t know why they’re so well established.

“If you look at it this way, nature is very stable and has evolved these niches of microorganisms. It would seem naive of us to say, ‘Oh, we have a compost that we’ve imported from another area with foreign microbes, and we’re going to throw some on the soil and change the whole population and improve it.’ From the perspective of the microbes in the soil, that would be a dangerous thing, because they represent the best and well-adapted organisms in the situation.”

When we apply composts to soils, Brinton concluded, we’re actually feeding indigenous microbes and trying to increase their activity in the soil, not replacing them with superior microbes, “which, as far as I know, do not exist.”

An indirect impact of compost, such as foliar fungal disease control, has been proven in many studies but is very unpredictable, with a “good year/bad year” effect. The scientific community, said Brinton, is very uncertain about this idea of disease suppression from compost. “This unpredictability is based on the fact that we don’t understand the microbial systems in which we are working.”

Brinton mentioned a study done in Germany in the late 1980s in which almost complete control of late blight in potatoes was achieved with compost applications. “You could look at a field and see dead squares and living squares of potatoes. Every green square was where the compost had been. The following year, several companies commercialized compost extracts, got patents on them – the equivalent of EPA registration in Germany for application of these to potato crops. The following year when disease hit, there was no control at all.”

The hygiene effects of compost, such as promoting litter decay on the soil surface, were much larger than expected. This is a common sense approach to compost: Use it in the fall to help the detritus on the surface of the soil to decay.

Predicting N Release from CO2 Bursts

Brinton has been working in a new area for the last few years. “What is the real impact of compost on soils,” he asked, “and how can we use it to predict fertility in order to better fertilize – and not over-fertilize – an organically managed system?”

Woods End Lab has been working with a USDA-ARS Soil Lab in Temple, Texas, run by Dr. Rick Haney, to measure the burst of CO2 from soil before and after compost applications. In a study last year at Atlantic Organics Farm in Bowdoinham, applying 20 T/A of compost to several fields increased respiration in the soil by 25 to 30 percent. “That’s where the nutrient supply is coming from when you add OM to a soil,” said Brinton. “The burst of CO2 correlates with N and P release to plants.” Brinton is now studying the relationship between that burst and nutrient release and crop yield.

Recently published findings from the study, including data from fields in Texas, show that compost field applications are linearly correlated with respiration, as measured by the 24-hour CO2 response; and that 28-day N and P mineralization correlated closely with one-day CO2 from drying/rewetting tests.

“You could almost draw a straight line” correlating the release of CO2 with the 28-day release of nutrients, said Brinton. “The USDA group in Texas is very excited about where this is going, because we’ve taken this to farmers to show them that now we’re going to measure their CO2 burst, and we can predict the N and P that their soil is going to release. Most of them tell us, ‘We don’t believe you.’ We sat down with one farmer with maybe 2,000 acres and calculated the N savings for him, and he still didn’t believe us. So we invited him to cut our recommendation in half, since we were not obviously telling him the truth, and test it on part of the farm. At the end of the season, the farmer reported that he’d saved $30,000 in fertilizer, and his yield was as great.

“It’s like the farmers don’t even want to save money when you give them the opportunity, because they’re so into the existing system of nutrient testing, N recommendations. They pay no attention to what’s in the soil already. They completely ignore the OM when they make their N recommendations. When we come in with a very carefully prepared test, to them it’s just too good to be true. So we’re having a really hard time presenting this information in conventional audiences. They’re the ones spending an incredible amount of money, while fertilizer prices are continuing to rise.”

Brinton showed data demonstrating that the soil CO2 burst correlates closely with N mineralization from composts – but a few data points were significantly off. A huge amount of N was being released compared with the respiration rate. When Brinton and his coworkers checked those fields, they learned that farmers had applied commercial, pelletized fertilizer in those plots in addition to the compost applications – supplying far more N (70 ppm soluble N) than the crops needed.

Solvita jar
The color on the CO2 probe in a jar of soil is matched with a color chart after 24 hours. Photo courtesy of Will Brinton, Woods End Lab.
Solvita chart

These studies are based on a respiration procedure invented at Woods End called the Solvita Test. “I’d been doing these titrations of CO2 for the last 30 years and getting increasingly sick of the wet chemistry of them, so I took the chemistry of them and put it into a gel, and we put the gel on a paddle, and we stick the paddle in a jar of soil. It soaks up the CO2 and it changes color in proportion to the amount of CO2 being produced. The new USDA test procedures correlate the color of that gel with the N released based on the CO2. We’re getting excellent correlations now, so we think we have a really good method that would help predict this N release from compost. What I like about it is that it validates that compost is feeding the soil and causing this burst of nutrients.”

So, said Brinton, studies have proven that a soil CO2 respiration response occurs at modest application rates (5 to 20 T/A) of compost, and the soil CO2 burst correlates directly with N and P mineralization. “That’s really great news, because within organic farming, we’ve always said there was an organic P cycle, but you could probably read more papers refuting that because P tends not to be held in organic complexes. Yet we are getting as good correlations with P as with N. Compost is somehow stimulating that whole organic N-P cycle.”

However, the soil solution C:N ratio significantly impacts natural release of N and P. “If the C:N ratio is too high, microbes spend all their time trying to chew down the C, and they’re not going to release any nutrients. Some people call that N immobilization from putting on too much crude OM. We’re seeing that it’s more deeply embedded; that it’s very hard to affect that C:N ratio in the soil in a short period of time. If the C:N ratio is high, you’ve got to do more to stimulate the N cycle to pull down that ratio, because you won’t get a good response to compost; and that leads to compost over-fertilization. Growing legumes is one of the most natural ways to raise organic N in the soil without pushing it too hard with nutrients. I think we could improve the situation and it would result in an increased ability of our soils to be highly responsive to compost.”


Brinton said to apply well matured compost so that the C:N ratio does not negatively impact soil microbes. “We have a lot of C in our soils in New England. On my farm, my soils are 6 to 7 percent OM. I don’t need more crude OM on the soils. I need to manage it well so that the turnover rate is satisfactory. I certainly don’t want to put on compost that is still busy breaking itself down and still has a relatively high C:N ratio. There are commercial products out there that have relatively high C:N ratios, particularly if it’s leaf and yard waste compost. It can be quite woody and have a high content of leaves. That will preoccupy the soil microbes considerably.”

The OM condition of the soil itself significantly impacts its responsiveness to compost applications. “We’re going to start looking this year at the soluble C:N pool in the soil and tell what the CO2 burst is. We’ll be able to give you a picture of the condition of the soil. It’s like measuring the potential response of organic practices.” Growers who are interested in obtaining a CO2 burst test can contact Brinton. (Woods End Lab, P.O. Box 297, 290 Belgrade Rd., Mt. Vernon, ME 04352; (207) 293-2457 or (800) 451-0337; [email protected]www.woodsend.org)

The positive effects of compost accumulate over time. Be patient, said Brinton. Don’t push the compost applications.

Asked about using compost tea, Brinton said that people send him samples of tea that measures about 100 ppm OM. “It’s so dilute. I say, you’re going to put 3 gallons on an acre and tell me that has any effect? Ten tons per acre of compost sometimes has a barely measurable effect. I’m hearing people say things about microbes in liquid feeds and extracts that I think discredits microbes. They can’t do all these things that we say that they’re able to do. That same tea applied as a surface topical treatment to a fungal infected plant might have an effect if you put it right on the leaves that are relatively clean at the time – it might have a chance of doing something.”

Asked if the CO2 burst from compost indicates a sudden release of N, when we’ve been told that compost provides a slow release of N, Brinton said that both are true. “We think that this drying and wetting cycle that our surface soils go through is like a pump. When OM dries and then the rain hits it again, there’s a huge burst of CO2 and a sudden pulse of N, and then it tames down again.” So the drying and wetting cycles that soils are subjected to, rather than a consistent moisture level, may be best. “Meanwhile in the background, the OM is constantly breaking down. So both things are going on.”

Brinton was asked about two composts made with the same high N ingredient but one using straw and the other, sawdust for C. “Will one be better than the other?”

Brinton responded, “You will probably have two very different composts. The C:N ratio of sawdust is 200-plus. I’ve seen it at 1,000. It depends on the composition of the wood. Whereas straw is 50 to 60. The straw is also mostly cellulose, while the wood is lignified matter that is very slow to be microbially digested. I’ve often told people that the worst combination for compost is something like chicken manure and sawdust. Chicken manure has a high availability of N; sawdust has a high availability of C. When you put them together, I don’t think they even see each other. But with straw, they’re like, we can do this together because we’re not too dissimilar. Straw is relatively unavailable in modern farming systems, but it makes great compost. I always encourage people to use something like mulch hay rather than sawdust.”

Because a conventional potato crop has 15 or 20 fungicide applications a year, we need an alternative – so Brinton was asked whether the compost extract work is continuing in Europe. He said that compost tea combined with what he calls the quantitative application of compost – getting compost into the soil system – could really combat potato diseases.

“When I did those studies in the ‘80s in Aroostook, making compost out of potatoes, there was a lot of resistance to doing that work up there. I heard farmers at meetings saying, ‘He’s just going to spread diseases all over the place.’ The Maine Potato Board wasn’t sure they wanted to support this kind of crazy attempt to make fertilizers out of potatoes. When they finally let us do the field plot study, we took them out to the plots that had compost in the soil from composted diseased potatoes at the lowest disease incidence. That’s when the interest started growing. They said, ‘Wow, you can make compost from a diseased plant and soil resistance goes up.’ Well, it shows you that those soils needed OM.” Brinton thinks that combined strategies, not a silver bullet, can address disease problems.

Asked about using less dilute compost teas and adding a spreader-sticker, Brinton noted that German researchers always said do not dilute the teas. “When I told them I saw California growers diluting them in 2,000-gallon tanks, they shook their heads and said, ‘That’s not what we said!’ They said keep it concentrated, so that’s exactly right. That’s a lot of hard work. That’s a lot of compost going into a liquid. What do you do with the slop after you’ve extracted [the tea]?”

Asked if tomatoes with late blight should have been composted, Brinton said he thought they should have been burned to destroy the disease spores. Eliot Coleman noted that W.J.C. Lawrence of the John Innes Institute had a plot in the ‘40s where he composted blighted tomatoes and used the compost on the same plot where he then grew tomatoes. Over the years he had far less disease on those plots than on the ones getting other compost. Brinton said that a grower can’t take a single year loss, but a researcher can.

Asked if compost can get too old, Brinton said he has some 6-year-old compost on his farm that he mixes with peat moss and uses to start seedlings. “It suppresses damping off nicely, it’s high in soluble N as a result of the slow decay. I don’t think compost ever goes bad in that sense.”

Eliot Coleman: Plant Health Through Soil Fertility

Eliot Coleman of Four Season Farm in Harborside, Maine, talked about building soil fertility to grow healthful plants and to decrease pests.

“When I read my first book about organic agriculture years ago,” said Coleman, “the thing that fascinated me most was the idea that if you grew plants correctly, they didn’t have pests or diseases.” He’s been collecting studies related to this idea for more than 30 years now.

Coleman read a story called “The Grower” from the 1978 book The Pesticide Conspiracy by Robert van den Bosch, in which a farmer boasts to “the rawhide” next to him on the bar stool: “‘We really busted the bastards. First we hit ‘em with two pounds of methyl and then mopped up with Big Daddy. I swear there ain’t a bollworm left on the whole damned ranch.‘ The rawhide says nothing but slowly nods approval as the respect bordering on love that macho men hold for each other glitters in the ice of his eyes.”

“That’s what’s going on,” said Coleman.

Coleman then made up some stories that address the symptoms of a problem instead of correcting the cause, such as pulling a broken down car with a horse.

Likewise, he asked: “If I have a headache, is it because of a deficiency of aspirin in my body? If I take aspirin, the pain is masked by taking the aspirin. I’ve treated the symptom. And as long as I make Mr. Bayer happy and I take enough aspirin, I’m not going to feel the headache. However, if I’m interested in correcting the cause of the problem, and I realize that my hat’s too tight” – and then he removed his hat – ”no more headache.”

Then he asked, “Is there a cause for pests and diseases in agriculture? I contend there is.”

One study he co-authored (“Role of Stress Tolerance in Integrated Pest Management,” by Eliot W. Coleman and Richard L. Ridgway, in Sustainable Food Systems, Dietrich Knorr, ed., 1983) had five pages of citations of published research articles showing that if plants were grown correctly, they did not have pest and disease problems. There is an enormous amount of published literature on this subject, he said, and it’s published in the same entomological journals that are supposed to be read by academic entomologists and people who tell us we can’t grow a crop unless we spray the bugs.

Insects do not eat indiscriminately, said Coleman. “If they did, long ago they would have defoliated the world.

“So why is the world still green? Insects have nutritional needs that cannot be met by eating a plant that is put together correctly. The same applies to diseases. It’s like if you were being asked to eat sawdust. If you were a termite, you could do it pretty successfully, but a human would starve. Until the late 1800s, everybody realized this. This was the standard understanding of the relationship between pests and diseases. When the Greeks saw fungus on a plant, they realized that the fungus did not cause the plant’s problems; the fungus was there because of an internal disorganization in the plant that was allowing it to grow. The secret was to correct the cause, not treat the symptom.”

One of the leading researchers in the 1800s was H. Marshall Ward, who taught at Cambridge, and one of his leading students was Albert Howard. The predispositionists – people who thought like Ward – ”held that pests or diseases could not be effective unless the plant was predisposed, weakened in some way that allowed them to get ahold. For them to become dominant, the plant had to not be itself. In other words, the pest-free plant is not the normal plant with something added; it’s the normal plant with nothing taken away. It is as it’s supposed to be, but our methods of cultivating it don’t allow it to be that.”

Wildlife biologist Farley Mowat, author of Never Cry Wolf, learned this when he was sent to Canada to find out what was killing the caribou. “He saw dead caribou everywhere and wondered why the wolves waited until 1932 to do this,” said Coleman. His Eskimo guides told him the wolves cannot catch healthy caribou, only weak, sick and unfit ones. A guide named Ootek told him that wolves were the best thing that had ever happened to the caribou because they maintain the quality of the herd. Other wildlife biologists later found Ootek’s thesis to be true.

There is a similar balance in plants, said Coleman. “Our work on this has been fascinating. We grow crops in greenhouses and outside, with no need for pesticides, because we grow them well. There is one flaw in this whole idea: You can’t sell it. You can’t sell the idea [that] you don’t need to buy anything.

“If we take advantage of what mother nature has provided to us – with green manures, crop rotations, cover crops, compost – we’re not buying anything. Small-scale organic farming is probably the most subversive activity on the planet today.”

So much research funding comes from [sources] interested in selling products, that doing research just to benefit farmers, where there is nothing to sell, “just isn’t happening,” said Coleman.

Yet a wealth of information shows that healthy plants resist pests. It’s been postulated that when plants are stressed, said Coleman, they become better food for herbivores. Plant hormones produced in plant roots enable healthy plants to synthesize amino acids into proteins. When plants are stressed, the hormones aren’t made, and free amino acids accumulate. Insects can nourish themselves on free amino acids, “not on properly put together tissue.” (“The abundance of invertebrate herbivores in relation to the availability of nitrogen in stressed food plants,” by T.C.R. White; www.springerlink.com/content/x24167v546840uq6/)

The USDA in Beltsville has been growing a vetch green manure, cutting it and leaving it as mulch, said Coleman, then planting tomatoes through it. They’ve also transplanted tomatoes into black plastic mulch on soil treated with conventional fertilizer. Tomato plants grown in the vetch mulch were healthier, more productive, more disease resistant and lasted longer in the fall. A USDA gene specialist said genes for disease resistance and longevity were not turning on in plants in the black plastic/chemical fertilizer plots. (“An alternative agricultural system is defined by a distinct expression profile of select gene transcripts and proteins,” by Vinod Kumar et al., Proc. National Acad. Sci., July 20, 2004; pnas.org/cgi/doi/10.1073/pnas.0403496101)

To grow healthy plants, Coleman has used a chisel plow on a tractor or, for a garden scale, a broad fork. “Compost, pH, soil moisture (not too much, not too little), soil aeration, avoiding compaction – all of these are part and parcel of providing the plant with the optimal growing conditions.”

Regarding defense capabilities, defense mechanisms and defense strategies in plants, Coleman said, “I don’t want to talk about this as if it’s a war. This isn’t a war, and bugs aren’t the other guys. This is learning to work with the way nature is operating. And the more we created ideal soil conditions, the better things got. The potato beetle was one of the tougher ones, and the other was the little white butterfly. For the last five years, the little white butterflies have been fluttering all over our farm, and we haven’t had a single green worm on the broccoli, on the cabbages or anything else.”

Coleman related visiting a farm in Vermont with severe potato beetle pressure. He learned that the stresses included fluctuating soil moisture levels and a soil that was too warm. Potatoes “don’t like warm soil.” When Coleman researched growing plants out of season without added heat, he learned that the more a soil sloped to the south, the warmer it got. So the east-west rows of the hilled potatoes in Vermont were too warm, and when they were hilled, one-third of the potato root system was destroyed. When Coleman started mulching his own potatoes with spoiled hay, the potato beetle incidence dropped 90 percent. Good soil aeration reduced the problem even more.

Not all of Coleman’s trials have succeeded. Using overhead irrigation on his greenhouse tomatoes was problematic, he said.

When he started farming, he would divide his field into strips of crops, and across the strips he would use manure in one part, seaweed in another, leaves in another, etc. “We would see root maggots wiping out the cabbages in the manured plots but not a single cabbage lost to root maggots in the autumn leaf section.”

Frances Chaboussou researched such effects for years and wrote Healthy Crops – A New Agricultural Revolution (Jon Carpenter Publishing, 2005). “There’s tons of stuff like this out there,” said Coleman.

Coleman outlined the different approaches of chemical, organic and biological agriculture, using this table:

Symptom treatmentSymptom treatmentCause correction
Presence of negatives (pests)Absence of negativesPresence of positives
Very shallowShallow organicsDeep organics
Use synthetic N, P, KSubstitution – dried blood, bone meal, banana peelsAsk how the natural system works. For example, what kinds of plants follow other plants in succession in nature?

“There are all sorts of things – I call them 1 percenters, and I think they’re cumulative – that go beyond what the USDA thinks organic is,” said Coleman, adding, “Nature is in charge. If this is true for plants, is it true for animals? For us?”

He related telling a group from Oral Roberts University, “Here is this nonbeliever – agnostic/atheist – who believes that whatever, whoever or however the world was designed, it was designed perfectly; and if there are flaws in our ability to work within that, they come from our misunderstanding, not through some fault of the design or the designer. I said, if you people look at your lives … you will realize that … you believe that the world was designed really poorly, and thank goodness Dow and Monsanto and Merck and all these people came along to bail us out. And I said, ‘How come this nonbeliever thinks the world was designed elegantly, and it’s up to us to figure out how to plug into it, and others believe it’s quite inelegant and needs all that help?’”

So, said Coleman, “that’s my association with this idea for some 40 years. We just make good compost, we aerate the soil. We put on as much compost as we can – some of this information today I didn’t agree with; the OM level in some of our greenhouses is up to 15 percent – and things grow better all the time. If I can get ahold of outside OM for the farm, I have purchased it. We will be getting livestock this fall, because I like that cyclical system. But extra compost makes things work.”

Asked why his crops resisted cabbage worms, Coleman said either the butterflies didn’t lay eggs on the plants, or they laid eggs but the larvae didn’t develop. He noted that aphids can be winged or wingless, and the literature shows that winged aphids form when plants don’t offer what the species needs. He said that for young cucurbit plants, he does use row covers for a few weeks. “Those plants do not like to be transplanted, especially going from my warm greenhouse to outside, where it’s cool.” By the time he removes the covers, cucumber beetles are not a problem. “When I create stress [on a plant], I have to deal with it.

“What prevents root maggots in brassica crops is nitrogen,” he added. “If you read old books, farmers figured out that if they just put a little extra kick of sodium nitrate on their cabbage, they had no root maggots. When I put my very earliest broccoli out – around the 19th or 20th of April, as early as I can – we put them under row cover.

“We have gotten the soil to the point where it works. It takes some time for these systems to get themselves working.”

Asked what he thought about permaculture, Coleman said that it consisted of ideas – many of them good – that had been around for a long time, and that Bill Mollison gave a name to these ideas and created a cult. “I’m just not a cultist.” The idea of planting with other families, of having variety in the garden, is wonderful, “but as a farmer, I need my production to be a little more driven than what I could do with permaculture.”

Asked about seaweed, Coleman said he harvests it with a linoleum knife, leaving 3 to 4 inches of holdfast attached to the rocks, and it grows back. “It’s incredibly productive.” He puts it in his compost. But he farmed without seaweed in Vermont for 10 years and his soils did well there too.

He suggested his book The New Organic Grower as a guide to his methods – mentioning, however, that he no longer thinks we need as much phosphorus as he thought when he wrote that book. In old books, he’s read that you can get N from legumes and K from manure, but nothing mentioned had P in it, so he wondered if nature had a reason for this.

Asked about plant varieties, Coleman said that before pesticides were developed, plants that were selected had to resist pests naturally, so many heirlooms should have some pest resistance. Many crops that have been bred for industrial agriculture are less likely to resist pests. He has faith in varieties developed by seed houses such as Johnny’s.

He did not notice a problem with early blight on his tomatoes last year. All his tomatoes are grown in a greenhouse.

– Jean English

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