Experts Talk Soil at MOFGA Meetings
by Jean English
Jerry Brunetti is the managing director of Agri-Dynamics, a soil and animal health consulting company that also markets holistic remedies for animals in Easton, Pennsylvania. At MOFGA and Cooperative Extensionís Farmer to Farmer Conference in November, he spoke about improving soil chemistry and soil health through diversified cropping systems and amendments.
Working primarily with "Plain Folk" (Amish and Mennonite) dairy farmers in Lancaster County, Brunetti finds that these farmers have to deal "as much with overfertility as anything else." They have "good, high-calcium soils," but because of the high animal population in Lancaster County, they also have an "overkill of phosphate and potash. Potassium will be taken up a lot more readily than calcium, leading to cationic imbalances in the animals," said Brunetti. These imbalances "are not healthy."
Another problem in this area is that "the Amish like to get in their fields early, so they leave the soil bare over winter. Itís a challenge to get them to look at cover crops."
Third, Brunetti finds that Lancaster County soils often "have the fertility but itís not getting into the plant because of air, water or decay problems. Air management, water management, decay management and fertility management all affect one another."
Agri-Dynamics works with the Albrecht model of soil fertility, said Brunetti, which calls for calcium to comprise 65 to 75% of the base saturation; magnesium, 12 to 15%; potassium, 3 to 5%; hydrogen, less than 10%; sodium, less than 1 to 3%; and the rest, trace minerals. He recommends testing the soil at the same time every year, "otherwise, soil temperature and biological activity will affect the results." A soil test, added Brunetti, "is a guide to see if youíre going in the right direction. For more precise information, tissue testing" is required.
Brunetti pointed out that sulfate, borate and nitrate are all negatively charged ions, so they tend to leach. However, soils high in organic matter tend to hold these better. "The only way to affect cation exchange capacity is to add humus," he said.
Maintaining sufficient sulfate in the soil will enable plants to utilize available nitrogen better, since N is a component of all amino acids and S of some. Thus, when both nutrients are at optimum concentrations, "you get better protein content" in crops grown for animals. "To improve the sulfur concentration in the soil, get the organic matter up," said Brunetti. "When the N:S ratio is 10:1 or less, youíre probably getting pretty good forage quality, good quality protein," he added. The sulfur issue is one that may be overlooked in Maine, since less S may be coming into our soils as pollution and S is not reported on the standard soil test here. However, many growers add the element as sulpomag.
One source of organic matter can be red clover planted as a cover crop. In animal/cropping systems such as those Brunetti works with, soil microbes need a lush cover crop like this to help them digest the large amounts of straw that are being put back into the soil.
Brunetti illustrated the importance of the proper concentration of magnesium in the soil by explaining that excessive Mg will tighten up soils, since the element has cohesive properties. This cohesiveness can be "good for sandy soils" but if too much Mg is present in a soil, you may have to add some calcium. On the other hand, magnesium deficiency in cattle leads to a disease called tetany. This can occur in the spring, when magnesium is not becoming available in the soil as quickly as nitrogen and potassium are.
Regarding pH, Brunetti said, "If I see a low pH soil, I first look at the base saturation. If itís 28% hydrogen, that tells me thereís a soil fertility problem, because the hydrogen ion is the easiest to knock off of the soil colloid if calcium and magnesium are present." In a pH 5.2 soil, for example, heíll "try to get the base saturation of calcium up to 65 to 75%. If I can get that and 12 to 15% magnesium and 3 to 5% potassium, the pH will take care of itself."
He added that liming provides not just calcium to the soil and the plant, but produces a variety of other responses as well. For example, when calcium carbonate (lime) is added to the soil, some of the Ca taken up by the plant roots. In response (to maintain a balance of ions within plant cells), some hydrogen is released by root cells into the rhizosphere. Some of this H combines with some of the carbonate from the calcium carbonate to form H2CO3, which maintains an equilibrium with H20 and CO2. This CO2 (carbon dioxide) enriches the atmosphere of the plant canopy, enabling the plant to make more sugars (CH2O).
Brunetti talked about hardpan as a yield-limiting factor on some farms. "If you have hardpan, you need to subsoil so that roots can get down deep and bring nutrients up (and down). If youíre subsoiling, do it when the ground is not too wet and not too dry."
The importance of the 4 tons of microorganisms per acre of soil was described by Thompson and Troeh in Soils and Soil Fertility (1978), said Brunetti, when they said, "As below, so above." He said that fresh manure provides much greater biological activity to the soil than composted manure. A greenhouse study was mentioned in while composted dairy manure did almost nothing for soil aggregation compared with fresh manure.
A Proactive Look at Soils
Soil scientist Fred Magdoff pointed out that there can be problems with using ratios of base saturation as a guide to soil fertility. You can have a great ratio on a soil with a cation exchange capacity of 4, he pointed out, and have very little potassium or other elements available for plants. However, 90 to 95% of the soil samples he sees in Vermont are within the ranges of Albrechtís formula, Magdoff added.
Fred Magdoff continued speaking about the importance of soils at the Farmer to Farmer Conference. Magdoff is a professor of soil science at the University of Vermont and is chair of USDAís regional Sustainable Agriculture Research and Education program (SARE). He has been working on ways for farmers to build and maintain soil quality through wise use of nutrients, cover cropping and manures, and much of this information is in his and Harold van Enís book, Building Soils for Better Crops ($19.95 & $3.95 shipping & handling from Sustainable Agriculture Publications, Box 90, Hills Bldg., Univ. of Vt., Burlington VT 05405-0082; Tel. 802-656-0484; email@example.com.
Magdoff said that the concepts of "proactive" versus "reactive" are germane to how you organize a farm. The common way of dealing with pests and soil management to date has been reactive: You see a problem and react; you donít have enough potassium, so you add potassium. The proactive approach, he continued, is preventive. Like preventive medicine, you want to avoid getting sick--and you want to avoid problems on the farm. "How can we design systems so that we avoid problems?" he asked. "Itís an ecological design issue."
Knowing the difference between symptoms and problems is another issue. You may have a low fertility soil or a soil with poor structure, Magdoff explained, but these are symptoms of larger problems. "When we look at the huge quantities of nutrients that accumulate on farms, people say that is a problem. I say it is a symptom of an agriculture thatís out of whack. Itís an irrational, anti-ecological arrangement in agriculture." He suggests asking whether any given problem is really a symptom of a deeper, underlying problem.
Nature Versus Nurture
"We may not be able to have a good soil everywhere," said Magdoff. "Some soils are naturally less fertile than others." He talked about the nature of soils versus the nurture of soils. "Almost all soils can be improved, nurtured. Like our kids, we want them to live up to their potential."
Magdoff listed seven properties of well-nurtured soils. (The first three are commonly discussed traits of soils; however, they are not enough, Magdoff said.):
The key issue in managing soils well, in his opinion, said Magdoff, is the management of soil organic matter. Good organic matter management leads to healthy soils, which lead to healthy plants, which lead to sustainable agriculture, he said.
Organic Matter--Living, Dead and Very Dead
Magdoff described three types of organic matter, using terminology developed in 1908 by Vermont soil scientists J.H. Hills, C.H. Jones and C. Cutler. Organic matter can be living, dead and very dead. The percent organic matter in a soil measured by a soil test lab "is not the only issue, and maybe not even the major issue," he continued. "The type of organic matter is important."
The living portion includes bacteria, insects, nematodes, fungi, earthworms and plant roots. "Roots have a profound effect on the soil, and vice-versa," he said.
The dead portion is the active organic matter or particulate organic matter--"the organic matter that decomposes fairly easily." It consists of sand-sized particles of fresh residues extracted from the soil. You can still make out what material this organic matter was made from, whether fungi, leaves, and so on.
The very dead is the well decomposed organic matter, or humus. It is "passive in the sense that it will not readily decompose because itís already well decomposed. Itís fairly resistant to decay." Typically, organic matter comprises from 1 to 8% of agricultural soils, and 60 to 80% of that is humus; 10 to 20% is active; and 10 to 20% is living biomass.
Soil organic matter has profound effects on many soil properties, Magdoff continued. It is a source of plant nutrients, for example. The very dead portion has a high cation exchange capacity--greater by weight than clay--and has naturally occurring chelates that also hold nutrients.
Organic matter improves soil tilth by providing some of the structural material that cements soil aggregates. The hyphae of mycorrhizae apparently are especially important in exuding a sticky substance that stabilizes aggregates. These aggregates promote water infiltration as opposed to the erosion and runoff that occur when soils crust. "Crusting is a common phenomenon," said Magdoff. Some crusting can be harmful, by impeding germination, for example. As an example of the importance of the living portion of organic matter, Magdoff said that in one experiment of a 10-inch-diameter soil core, one worm hole conducted 10% of the water that infiltrated that soil.
Organic matter buffers against pH changes, Magdoff continued. "The more organic matter you have, the more difficult it is to decrease the pH of your soil."
It also protects against harmful chemicals. "Some soil tests are saying that if you have a high organic matter content, you donít have to have a high pH. You can grow barley at a pH of 4.5 if you have high organic matter, because the organic matter ties up aluminum, which barley is very sensitive to."
Organic matter darkens the soil, which helps it warm in the spring, possibly giving you a day or two head start on the planting season.
Soil organic matter is a carbon sink. "Thereís as much carbon in your soil if you have 1% organic matter in the top 6 inches of your soil as in all of the atmosphere above," said Magdoff. "Farmers may get paid in the future for building up organic matter and storing carbon."
Humic materials in soils stimulate roots to divide and grow longer, Magdoff continued. Even when plants are grown in nutrient solutions (hydroponically), if humic acids are added to the solution, more root growth occurs.
Organic matter helps maintain biological diversity in the soil, and "diversity is your protection" as natural, beneficial organisms keep potentially harmful organisms under control. Nematodes that are parasitic on plants are a very small percentage of nematodes in the soil, said Magdoff. Many of the others are beneficial, feeding on harmful nematodes, on fungal hyphae and so on. The soil is "almost like a war zone in which diversity is working for you. All of the organisms keep each other in check--the way our government is supposed to work."
You have to add organic matter to soils continuously, said Magdoff. "You canít slack off. You may miss one year, but not two." He cited a study in which growing continuous corn silage for five years reduced the organic matter from 5 to 4% of the soil--a 20% loss, which also added carbon dioxide to the atmosphere.
Losses and Additions
Organic matter decomposition is increased by intense tillage, warm temperatures, moist soil, light soil texture, and low lignin residues. Erosion is enhanced by low infiltration rates, which are caused by surface crusting, compaction and/or a lack of surface residues, by plowing up and down slopes, and so on. "Whatís actually going up and down is the active organic matter," said Magdoff. "The passive is not lost easily because itís not easily decomposed." Goals for managing soil organic matter should include, therefore, adding large quantities of organic matter; using different types of residues (from different species and/or sources); and reducing losses of organic matter.
Additions can be increased by using existing residues more effectively (donít spread manure in the winter, for example); by finding appropriate off-farm sources of organic matter, such as shredded leaves from towns; by changing rotations to include high residue and sod-type crops; and by using cover crops when possible. "Follow any crop by itself and you get a 10% yield cut just from the lack of rotation," said Magdoff. "No one knows the exact cause, but the rotation effect can increase yield by 10 percent."
Magdoff reiterated Brunettiís comment about the value of uncomposted manure: In one experiment that Magdoff did, compost did not help with soil aggregation as much as manure did, because the compost was already decomposed and therefore added no sticky substances to the soil.
Reducing tillage helps conserve organic matter on many soils. The real purpose of tillage, Magdoff explained, is to destroy aggregation in order to make a good seed bed. "Maybe zone tillage is one answer" to the question of how to maintain organic matter but have a good seed bed. "Maybe no-till systems will be developed for organic culture."
Evaluating Your Soil
One way to evaluate your soil is to evaluate your pest problems. Magdoff said, "Itís amazing what nature has done," as he told how many plants, when attacked by insects, secrete volatile compounds that attract the specific predator that attacks that pest. "These signals are enhanced in better quality soils," he said. One grower told him, for instance, that he had no insect problems on his organic fields, but many on his conventional. Likewise, when corn borer moths were released in a greenhouse in which corn was grown in conventional versus organic soil, "time after time, the moth wanted to lay eggs in the conventional corn. This is one of the exciting developments in the whole story of soil organic matter management."
One way to judge your soil is to look at it, smell it, feel it. Magdoff said that when farmers brought their best and worst soils to a workshop at the Rodale Institute, you could tell them apart by their odor (good ones have a nice, earthy smell), structure and color (darker being better). You can also use a penetrometer, which measures the force in pounds per square inch (psi) required to penetrate the soil. At more than 300 psi, roots canít penetrate.
Root development is a clue to soil conditions. Are roots well branched? Do they have good color? Are they growing laterally to avoid a compaction layer?
You can measure water percolation by cutting the top and bottom off of a coffee can, pushing the can into the soil, placing Saran Wrap over the top, carefully pouring about a cup to a cup and a half of water into the Saran Wrap, then removing the Saran Wrap carefully and seeing how long the water takes to soak in. "Taking measurements in different places will give different results," said Magdoff. "You need to reproduce measurements in several parts of the field to get an accurate picture."
You can also look for crusting after rains, and/or "go out in the middle of a rainstorm and see where runoff occurs." Magdoff talked about Steve Groff, a Pennsylvania grower noted for his use of no-till, cover crops and good rotations, who went out with a video camera during a rainstorm and taped runoff from his farm and from his neighborís. His farm produced much less runoff, and what it did produce was clean; the neighborís was abundant and turbid. (For more information, see Groffís website: www.cedarmeadowfarm.com.)
At the other extreme, during a drought you may see parts of your farm that do better than others, Magdoff added. This can tell you where to put additional compost. All observations and measurements should be carefully recorded and organized from year to year, Magdoff recommended. Some states are developing a soil card to help with these evaluations. It includes such items as soil color, number of earthworms, condition of roots, amount of organic matter, subsurface compaction, tilth, erosion, water holding capacity, infiltration rate and drainage. (Eric Sideman is interested in developing such a card for Maine soils.) Magdoff noted, as did Brunetti, that you have to make observations under similar conditions (of soil moisture and temperature, for instance) in order to be able to compare them from year to year.
In a brief discussion about reduced tillage, Magdoff said that you have to be careful with the practice because it eliminates the option of plowing to reduce compaction. One way to reduce compaction on no-till farms is to control traffic to certain areas of the field. "Itís better to pack the hell out of a small area of the field than to have less compaction in a larger area," he said. "Permanent raised beds are the ultimate in controlled traffic."
Responding to a question about what type of cation exchange test to ask for on a soil test, current or altered, Magdoff suggested always getting the current, and keeping track of it each year or two. (The altered test tells what the cation exchange capacity would be at a particular, altered pH; the current tells the CEC at the unaltered pH.) He added that testing the soil every two years is good enough, and Waldo County Extension Educator Rick Kersbergen added that soil test cost less if theyíre sent to U. of Maine between Jan. 1 and April 15; he also said that the soil should be held at room temperature.
Cover Crops and Soil Fertility
Marianne Sarrantonio is the author of The Northeast Cover Crops Handbook, was a researcher at the Rodale Institute, and joined the faculty of the Sustainable Agriculture program at the University of Maine this winter. At MOFGAís Spring Growth Conference in Unity in March, she talked about using cover crops to build soil fertility.
Sarrantonio outlined four basic ways to do this:
As an N source, legumes can make available or contain as much as 300 pounds of N per acre, although 100 to 150 pounds is more common. Approximately two-thirds of this N is "fixed" from atmospheric N when rhizobia bacteria living symbiotically with legume roots take N out of the atmosphere and convert it to a form that plants can use. Plants in return supply the rhizobia with carbohydrates. Some 20 to 60% of the N in legumes generally is available to the next crop. The variation occurs because this N is released by decomposition, and environmental conditions impact decomposition. Very dry, wet, acidic or mineral deficient soils limit microbial activity. The N that isnít released may be retained in residues in the soil or in microorganisms; this, said Sarrantonio, "is a key difference between providing N as a legume versus as a bagged fertilizer."
To tell if the rhizobial relationship is working, Sarrantonio said to carefully dig up the plant, wash its roots, and look for large nodules that are clustered around the main part of the root. Break a few off, break them in half and look for a pink color inside. If theyíre green, white or black, N fixation is not occurring. You are looking for a lot of nodules, large nodules (if that particular plant has large nodules; hairy vetch does not), and active nodules.
"Just because you plant a legume doesnít mean youíre getting N fixation," said Sarrantonio. "You need the right rhizobia in the soil. Thereís a close match between the type of legume and the rhizobia. Vetch [rhizobia] is different from clover, which is different from soy... Itís important to spend $2 and inoculate the legumes youíre planting. The rhizobia may [already] be in the soil, but there may not be enough of them," and they are competing with other soil microorganisms.
The rhizobia that you buy is packaged in a peat substrate. It needs to stay moist and relatively cool, and even under these conditions is good only for about six months, so check the date on the package, Sarrantonio advised. "The number of live cells plummets precipitously after the expiration date." She encouraged conference participants to tell their farm stores to refrigerate inoculum, and she advised against using Ďmultipurposeí inoculum, since you are putting competing rhizobia right on the seed with the desirable rhizobia.
To use the inoculum, moisten the seeds slightly, mix them with the inoculum, then plant them as soon as possible. Some people recommend adding a sticking agent (Kool-Aid is sometimes recommended) to help the bacteria adhere to the seed, but Sarrantonio believes that that may promote fungal growth. Milk does seem to work, she said, but she prefers to use water.
"If youíre going to grow the same legume two years in a row, you probably donít need to inoculate," Sarrantonio continued. "Past that, itís worth inoculating."
Conference participant Dave Colson noted that he uses a spinner to sow his seed, and if the seed is too wet, the spinner doesnít distribute it well. "If the seed is that wet," Sarrantonio responded, "itís too wet. Let it dry for half an hour or so before seeding. A pound of seed needs maybe 1/2 teaspoon of water to get the inoculum on."
The amount of N fixed varies from 20 to 300 pounds per acre. "Some legumes are inherently poor fixers," said Sarrantonio. The common garden bean ( Phaseolus ), for example, "never pulls its own weight. You need to add N." Hairy vetch and alfalfa, however, are excellent and "may provide 85 to 90% of their own needs by fixation." The length and temperature of the growing season impacts fixation; temperatures between 70 and 90 degrees F are optimum for the process. The health of the crop is important. "The legume is feeding the rhizobia. If [the legume crop] is not in good shape, itís not providing enough carbohydrates." As mentioned, the proper strain of rhizobia is critical; and environmental conditions, such as soil moisture, can influence fixation.
Sarrantonio presented the following data to show that fixation varies with cover crop species. The legume was overseeded into spring broccoli in Pennsylvania to fix N during the month between summer and fall broccoli crops there. Yield data were from Aug. 20 harvests.
Species, kg/ha, N kg/ha
Cowpeas produced the most nitrogen--79.9 kg/ha (roughly equivalent to pounds/A) in five weeks. Although the data would be different in Maine, Sarrantonio thinks that cowpeas are "worth looking at."
The Fate of N
What happens to the nitrogen thatís fixed? A small amount may leak during growth, but most of it is going into the legume, Sarrantonio said. The main benefit to the crop comes after the legume dies and begins to decompose, however. Since most of the N is in the tops of plants, if you remove the top growth from a crop such as alfalfa or clover, only a little N remains in the roots. You need to get into a system of using cover crops to get the accumulated benefits of these plants, said Sarrantonio.
"Tillage has a tremendous effect on how much N is available" to a crop, Sarrantonio continued. In conventional tillage, N can be placed as deep as 8 to 10 inches down in the soil by plowing, but no roots grow at that depth early in the season, so N is vulnerable to leaching. In a no-till system, on the other hand, N is concentrated in the top few inches of soil, so there is less chance of leaching. When organic residues are left on the surface of the soil, there is a greater chance of nitrogen going off into the atmosphere, however. "You often see a reduced benefit of a legume when it is left on the surface." The solution may be shallow tillage, Sarrantonio speculated.
Organic matter is important because it improves soil aggregation and tilth, said Sarrantonio; it increases the cation exchange capacity of the soil (the net sum of negative charges in the soil), thus is the key to keeping nutrients in the soil when plants arenít using them; recycles nutrients; provides habitat for microorganisms; and increases the water holding capacity of the soil. "Some organic matter can hold up to 20 times its own weight in water," said Sarrantonio.
Typically, non-legumes increase the organic matter content of the soil more quickly than legumes, because the succulent, nitrogenous legumes are decomposed quickly by microorganisms. Non-legumes have more carbon relative to nitrogen, and high-carbon material usually doesnít break down so quickly, Sarrantonio explained. Thus, grasses break down more slowly than legumes and may even tie up N as they are breaking down. One solution may be to grow grass-legume mixtures. Sarrantonio related another that she saw in California: Crop of fava beans (high N) was grown, cut, and laid on the ground, then was covered with straw (high C) in a sort of sheet composting process.
In addition to providing nitrogen and holding nutrients, cover crops can protect against erosion. They can increase water infiltration rates; their roots can stabilize slopes; they can decrease the physical impact of raindrops on soil structure; and they can slow the velocity of runoff.
One example of a cover cropping system, said Sarrantonio, is overseeding peppers with white clover and ryegrass in the summer to protect the soil in the fall. To protect soil in the spring, winter annuals such as hairy vetch can be sown and then mow-killed in the spring. All winter annuals can be mow killed, she noted. The soil may stay a bit cooler in the spring using this method, and fungal diseases and slugs can build up as well. As an example of a mow-kill, no-till system, she said that corn can be drilled into live vetch, then the vetch can be mowed after a few weeks. In field trials (not in Maine), this system added 10 days of growth to the vetch. In another example, tomatoes were planted into hairy vetch and rye. The cover crops kept the weeds down and the vetch added enough N for the tomatoes. MOFGAís technical director, Eric Sideman, noted that this system works better in the south than here because of climate differences.
Sarrantonio showed a graph comparing the amount of N taken up by September-seeded cover crops (again, not in Maine) to make the point that significant amounts of N can be conserved by using cover crops. She said that among the crops used, cereal rye (the same as winter rye) is best for Maine:
The key, said Sarrantonio, is getting the cover crop planted early enough "to do the job."
A possible added benefit of cover crops, Sarrantonio continued, is that mycorrhizae may enable these plants to take up nutrients--especially phosphorus--that are outside of the normal rooting patter. "Legumes tend to have good mycorrhizal relationships," she said, "probably because of the nitrogen. You may not notice the benefit [immediately], but once P is in the legume and the legume is plowed down, P is now in a more available organic form."
Dave Colson asked Sarrantonio about managing yellow sweet clover, a biennial that grows quite large. "How would cutting it during the second season affect N fixation?" he asked. "Typically," Sarrantonio answered, "when you cut any legume that will regrow, you get a temporary cessation of N fixation while [the legume] reestablishes its growth. Also, the clippings add N to the field and can shut down N fixation. You might cut it and remove it to keep the soil Ďstarvedí for nitrogen."
Eliot Coleman asked whether, over a 13-month, June-through-July period, it would be better to grow sweet clover as a cover crop for the entire period, or grow cow peas followed by rye and vetch. "From a soils point of view," said Sarrantonio, "sweet clover would probably be better because you donít have the added tillage. From the point of view of mixed residues and being easier to work with in the spring," the second option may be better. "But not too much is better than sweet clover," she concluded.
Kersbergen on Assessing Soils
Rick Kersbergen of U. of Maine Cooperative Extension told how to assess soil quality using simple tools and how to manage soil organic matter at the Spring Growth Conference. "What changes are occurring on your farm? Are you improving your soil health?" he asked.
To illustrate one simple way to assess soils, he showed two soils that he keeps in his office--one with peat moss and manure additions, one without; both are kept moist. The vast difference in color of the two can give you an idea of how different management systems affect soils, he said.
"We destroy soil health every time we plow, till or cultivate," he said. "We improve it when we add organic matter." Adding organic matter also helps the soil respond to the negative impacts of whatever tillage is necessary. Kersbergen reiterated Magdoffís assertion that raw manure "is much better than compost or cover crops in producing soil with good aggregation."
To judge the stability of soil aggregates--which determines the ability of the soil to resist breaking down--Kersbergen demonstrated how growers could put soil in a 1.18 mm screen, put the screen in a tray of water, and shake it gently. "Whatís left on the screen in terms of aggregates?" he asked, as he pulled it out of the water, showing the number of clumps remaining. He suggested screening rocks out of the soil first; and to get a better look at the size and number of aggregates, the soil could be sieved through screens of different finenesses.
Crusting indicates poor soil health, Kersbergen continued, and a single green manure crop is not going to reverse that illness. He echoed Sarrantonioís advice that growers need to develop long-term systems to keep soils healthy. "Eighty percent of a green manure crop can decompose in a single season," he said. "You need a continuum of green manure and fresh manure additions."
To measure compaction, Kersbergen showed a penetrometer, which measures resistance as it moves through the soil profile. "Rocks can be a problem," he noted, "so take multiple measurements." As an alternative, "you can just use a wire [or fiberglass rod--especially if youíre testing a hayfield or forage crop and donít want to risk having a cow ingest a lost wire]" as found on flags used to mark fields. Try pushing the wire into the soil between crop rows, within rows, at tire tracks... "It shows how roots would do going through the soil."
Kersbergen demonstrated the coffee can method of measuring water infiltration into soil, mentioned above by Magdoff, but used a 6-inch piece of stove pipe instead. Place a board on top of the stove pipe to drive it into the ground, said Kersbergen. When he has used this technique to compare how fast equal volumes of water penetrated soils that held sod or cover crops, the sod had the highest rate of infiltration. Kersbergen said that heís a big proponent of increasing sod in cover crop rotation systems. If sod is in place for two years with no tillage, "thereís great potential to increase soil health." However, there are tradeoffs regarding nitrogen additions and other inputs, he noted.
A pH meter, said Kersbergen, costs only $40 to $50 and is a good investment for growers. To use it, mix equal volumes of distilled water and soil, let the mixture sit for half an hour, then measure the pH in the soil slurry.
A Soil Health Test Kit, available from Gemplers and from Woods End Lab, costs $200 to $1000 and measures respiration and other parameters of soil health. And, of course, soil tests for chemical properties and organic matter content are widely available and use accepted, well established procedures to measure the nutrient status of soils.
When trying to maintain organic matter in the soil, Kersbergen reminded growers that "there is a big difference between manures. Poultry manure alone is not a good amendment. Chickens eat grains" and their manure does not contain much fiber. "Cows eat grass," so theirs is more fibrous. "Chicken manure is simply a fertilizer source; others are more fibrous and better food sources for microorganisms."
He noted that weed seeds in liquid cow manure that had been stored for three months were very low in viability, while viability of seeds in manure that had been stored in stacks did not decrease much.
Ingham on the Soil Foodweb
Dr. Elaine Ingham, another speaker at MOFGAís Spring Growth Conference, is a professor at Oregon State University and founder of the organization The Soil Foodweb, Inc., which provides growers with information on the health of their soil. After doing a double major in biology and chemistry at St. Olaf College in Minnesota and receiving her M.S. in marine microbiology from Texas A&M, Ingham went to Colorado State for her Ph.D. and Post-Doctoral degrees in soil microbiology. At Colorado, she developed a database of microbes in different soil types and found significant differences in foodweb structures in irrigated versus dryland wheat soils. Ingham continued her study of different soil foodwebs at the University of Georgia, where she looked at soils from agronomic crop fields, from different rotations, from forests and from the everglades. When she moved to Oregon State in 1986, she had the chance to study the soil foodwebs of environments ranging from rainforests to high cold desert. She now has a database on more than 80,000 soils from all over the world.
Ingham learned that the make-up of the soil foodweb depends on the plants growing in that soil, and that the plants growing in a particular soil depend on the nature of the soil foodweb. "Itís not a chicken and egg situation," she explained, but more of a feedback system in which plants do influence what lives in the soil, but a point is reached at which the web organisms have to be changed in order for new types of plants to grow.
Early succession tree species, for instance, such as poplar, birch and alder, start in soil that is dominated by bacteria but move the soil life to a fungal population. "Really productive forests" have 100 times more fungal than bacterial biomass, while the most productive forests have 1000 times more fungal than bacterial biomass.
Inghamís goal in studying soil foodwebs in different situations is to determine what foodweb system will enable growers to raise crops without depending on fertilizers and pesticides. She talked about the strawberry-growing region of California, where the early settlers were able to do just that for several years. After years of monoculture, however, productivity began to decline. After World War II, pesticides and synthetic chemical fertilizers became popular among growers--and pest populations increased. More fungicides were needed to fight the Verticillium fungus. Then the soil fumigant methyl bromide was employed to sterilize the soil so that root-feeding nematodes were also kept at bay long enough for a crop of strawberries to be grown. Starting in 1955, methyl bromide was used once very three years. By 1965, it was used every year, and by 1970, it was used on every crop rotation. For the last 14 years, methyl bromide has been applied two or three times a year in some areas. This option will soon be phased out, however, since methyl bromide depletes the ozone layer.
Ingham was called in to help find an alternative to methyl bromide. She studied soils in the nearby chaparral and found the original soil foodweb complex that had been destroyed by years of chemical applications in the strawberry fields. In the chaparral, sheep and cows grazed and plants grew with no inputs, and no harmful root-feeding nematodes were present in the soil. The valley soil where strawberries grew, however, contained harmful, root-feeding nematodes, spores of harmful fungi and other disease organisms, and was very low in bacteria. Ingham found that by replacing half of the volume of the soil in a strawberry bed with compost, she could get the soil back to a productive stage, with yields greater than those from the methyl bromide system. However, California does not have enough compost to amend that much soil, so Ingham came up with an alternative method of introducing beneficial soil organisms: She grew strawberry plants in plugs of compost for three weeks, then transplanted the plugs to the soil beds. The system worked: The first crop yielded 600 pounds per acre more than that using the methyl bromide system; and by the fourth time compost-plug plants were used, yields were double those of the methyl bromide system. "California is finding that it costs less to do sustainable strawberries than methyl bromide--but they have to know how to make good compost," she said.
She believes that adding organic amendments to the soil--humic acids, compost, compost tea, etc.--is necessary to keep soil life alive. If you add 100 pounds per acre of an inorganic fertilizer to a soil at one time, "youíre killing [soil organisms] basically through a salt effect," she explained, adding that those who use synthetic fertilizers would do better to use split applications--or to switch to organic amendments. Likewise, "Every pesticide has an effect on a soil organism," she said. "Every one is killing a beneficial organism." High concentrations of nitrate-nitrogen in the soil, as well as soil compaction, also kill beneficial organisms and select for disease-promoting bacteria.
"How do you get rid of plant feeding nematodes?" asked Ingham. "Get the competition in," including fungal feeding nematodes, bacterial feeding nematodes, and predatory nematodes. Also, mycorrhizal fungi help as their hyphae "make it difficult for root feeding nematodes to get through the soil to your root." The easiest way to get the competing nematodes in is to add compost. "You cannot buy them," she said. Mycorrhizal fungi, however, can be purchased and added to the soil. These fungi, she noted, do not survive composting.
The members of the soil foodweb, from the protozoa, bacterial, fungi and nematodes to the earthworms, centipedes, spiders, beetles and insect larvae, create a system in which diseases are suppressed, nutrients are retained and made available, toxic materials can be decomposed, and soil structure is built. The plant that you grow is part of that foodweb, too. Ingham told conference attendees to picture a plant growing in their field. "How many of you put the root system into it?" she asked. "How much of the energy from the top of the plant goes down to the roots? Sixty percent on row crops and vegetable crops," she said, and 80% in trees. "More than half of the plantís energy is below ground. That energy is used to grow structural roots to support plants...and lateral roots to take up nutrients." About 50% of the energy that goes into the root system is exuded into the soil as simple sugars, proteins and carbohydrates--"cake and cookies" for microorganisms, Ingham said. "Every plant has a different mixture of sugars, proteins and carbohydrates that it makes," she continued, and you can tell what plant, time of year and soil type is present by that mixture. The mixture is needed "to wake up critters needed to protect against disease." For example, a bacterial wall can form around a root system that will protect the root from disease: A white rot fungus just 1 mm away from the biofilm will not germinate.
The foodweb needed to fight diseases is complex. Ingham said that one cucumber cultivar growing in the presence of one type of fungal rot can require a succession of 12 species of bacteria to counter the disease. A different mixture of bacteria will be required at a different temperature, under different humidity conditions, and so on. Rarely is one disease organism present. "Your plants are challenged by about 1000 things that are trying to attack the root system. You need a lot of species to counter them. ĎBugs in a Jugí [commercial preparations of soil microorganisms] may only have five or six; one brand has eighty. Thatís not enough. You need to maintain as high a diversity as possible."
Not only can the proper soil foodweb help fight disease, but it may increase the nutrient content of plants as well. "You may not necessarily see bigger plants, but you will see plants with higher nutrient levels in them" when the proper fungal and bacterial populations are present in the soil. Grapes growing in a healthy food web, for example, had three times more protein than those growing in a depleted system. Wheat had 10 times more protein; organic produce had higher protein levels; concentrations of organic nitrogen can be increased, adding flavor to crops. "We taste proteins as being sweet," Ingham explained, and nitrogen is a component of proteins. Concentrations of every micronutrient are increased when plants are growing with mycorrhizal relationships, she added.
Nutrient Retention in Soils
Nitrate (NO3-) is the most leachable form of N in the soil, Ingham continued. The ammonium ion (NH4+) is the second most leachable form. Thus, she said, in agricultural soils, 80% of the fertilizer added ends up in the groundwater. On the other hand, bacteria and fungi are the least mobile forms of N in the soil. Bacteria make a "glue layer" that glues clay, sand, organic matter and other particles together and improves the structure and the filtration capacity of the soil. Fungi grow as long strands and bind soil particles together, and they make enzymes that enable them to "pull nutrients out of the soil.
"There is not a more concentrated form of N than bacteria on earth," Ingham said. "Bacteria are sinks of nitrogen. They make enzymes to pull in nitrogen." Plant roots do not make these enzymes, as plants evolved after the system of bacteria and fungi existed in the soil. Bacteria, she continued, maintain N as nitrate--the most efficient form of N for row crops to take up--by maintaining the pH of the slime layer between 5.5 and seven. Thus, the best soils for row crops are dominated by bacteria. For trees, perennial herbs and shrubs, ammonium is the preferred form for uptake, and fungi maintain that form.
Soil StructureBacteria "build the bricks" of soil structure with their slime layers, while fungi bind soil particles together with their hyphae. Then microarthropods and bacterial feeding nematodes create the spaces in those aggregates in which they feed on fungi and bacteria. This produces good soil structure--aggregates with air spaces.
When a soil is compacted, if a healthy foodweb exists, it will spring right back, Ingham said. Otherwise, root feeding bacteria and protozoa are left, the oxygen concentration drops, the aerobic organisms "go to sleep," and facultative anaerobes "turn on anaerobic enzymes" that produce alcohol, which kills roots; acetic acid, giving a smell of vinegar to the soil; butyric acid, which gives a sour milk smell; valeric acid, which gives the smell of vomit; and hydrogen sulfide, which has a urine smell. These anaerobic decomposition products turn the soil into hardpan.
Above Ground Foodwebs
Not only has Ingham studied the soil foodweb, but sheís looked at foodwebs on leaf surfaces and found that the right community of organisms there can fight diseases. Leaf surfaces produce exudates that can feed pathogens, she explained, so "you want to use those exudates for beneficial organisms so that infection sites are occupied" and pathogens canít become established. In one experiment, she sprayed 70% of a leaf surface with Botrytis cinerea, then applied Foliacin bacteria over 100% of the leaf surface. No disease occurred. She has done this with other pathogens and found similar results. "You donít need 100% coverage," she said. On grapes, 70% worked, but 50% didnít. She added that you need to apply beneficial sprays early to avoid foliar diseases, because pollutants, fungicides, dust, and other airborne particles can increasingly interfere with the process over time.
Making Good Compost
To make good compost, Ingham gave two recipes: one for bacterial dominated composts, which are used for annual row crops; and one for fungal dominated composts, which support growth of perennial plants (including strawberries). The recipes are:
After making the pile, it should heat to 135 degrees within 24 to 72 hours; if not, it doesnít have enough nitrogen, and/or pesticides in the material may have killed decomposing organisms. You can add a 1% sugar solution to the pile to feed the bacteria that can degrade the pesticides, said Ingham. If those bacteria have already been killed, they can be added back as "Bugs in a Jug"--i.e., commercial preparations.
The pile should heat to 155 to 160 degrees, when it should be turned so that beneficial organisms arenít killed. After turning the pile three or four times, the organisms should have "used up the juicy material" and protozoa should be proliferating. The temperature will now drop below 135 degrees. When the temperature is around 115 degrees, nematodes start to proliferate; this is the material that should be used to make compost tea, if that is your goal, and this material must be aerobic, said Ingham; if itís anaerobic, "youíre selecting for disease." If compost tea is not your goal, the pile can sit until it soon reaches the ambient air temperature, indicating that it is mature. If you turn it at this point and it heats again, it was not mature. As mature compost ages, the diversity of species that populates it increases for about six months; then diversity decreases, and after two years, it is "no different from topsoil" as far as microbial life.
Mature compost should have a moisture content of 15 to 50 percent, said Ingham. "Dig into the pile with your hand. Take a handful from the middle. If you can squeeze moisture out, itís too wet. If you can only squeeze one drop out, itís good. If you blow on it and can get dust off of it, itís too dry."
For more information, Ingham referred people to her website, www.soilfoodweb.com. Not only is her site packed with information, but readers can subscribe to her free e-mail magazine from the site. She can also be reached at Soil Feedweb Inc., 1128 NE 2nd St., Suite 120, Corvallis OR 97330; Tel. 541-752-5066; Fax 541-752-5142; or at firstname.lastname@example.org. Her site links to www.growingsolutions.com, where you can order an excellent manual on making compost tea. "Some of the most amazing stuff weíre working on now," she said, is controlling "botrytis, mildew, late blight, early blight, black spot on roses" and other diseases with compost teas.
Ingham was the primary author of Soil Biology Primer, available from email@example.com or by calling 1-888-LANDCARE (dialing the last E is not necessary; itís just there to make the acronym). This 54-page booklet, produced by the Natural Resources Conservation Service, is a well-illustrated (with many of Inghamís photos), easy-to-read introduction to what lives in the soil and why itís important.
Michigan Field Crop Ecology: Managing Biological Processes for Productivity and Environmental Quality, is available for $12 from Michigan State Univ., Bulletin Office, 10-B Ag Hall, East Lansing, MI 48824-1039. The 86-page booklet was written for Michigan farmers and edited by M.A. Cavigelli, S.R. Deming, L.K. Probyn and R.R. Harwood. Chapters include Field crop ecosystems, Soil ecology, Carbon, Nitrogen, Cover Crops, Pest ecology and management, The insect community, Nematodes, Directions for farm change, and Bringing it all together.
Better Homes and Gardens Special Interest Publications put out a magazine called Perennials in the spring of 2000 that had an article called "Soilís Alive!" by Ann Lovejoy. The article is an excellent introduction to the field of soil life, with good illustrations and a photo essay that shows how to make compost tea.
Other resources, including soil microbiology textbooks, are cited on Inghamís webstie and in the comprehensive bibliography "Soil Biology Educational Resources," available from USDA Natural Resources Conservation Service Soil Quality Institute, 2150 Pammel Dr., Ames IA 50011; Fax 515-294-8125; email firstname.lastname@example.org or email@example.com; website www.statlab.iastate.edu.
Minerals and Rock Powders
Agricultural Alternatives Consultant Mark Fulford, who lives in Monroe and has been farming for 25 years, spoke about the use of minerals and rock powders at the Spring Growth Conference. "There are lots of poor, sick, tired out soils in New England," he said. The combination of geological processes, weathering, environmental pollution and poor practices has depleted soils of a lot of their mineral content and biological activity. "Some soils have all the minerals but not enough life. Others have the opposite." You must build the soil foodweb and the mineral content of the soil; "You canít have one without the other," said Mark, explaining that the microorganisms are the "delivery system" for the minerals.
When Fulford has seen fruit trees growing in younger soils that have more igneous material than our New England soils, he has observed that the trees are healthier. He listed many characteristics of crops grown in soils that are deficient in available minerals, versus those from soils that are rich in minerals:
Plants and Livestock from Soils Deficient in Available Minerals:
After observing better plant growth on younger, more mineral-rich soils, Fulford became interested in paramagnetism--the weak magnetic fields inherent in these minerals. "There is an electrical and magnetic component of the soil, and you can use it to cut down on diseases, increase productivity," and more, he said. When he began using paramagnetic rock powders and minerals on his farm, he found greater mineralization of the soil in the living base, less trouble with climate zones (i.e., crops had 2 to 3 degrees more frost resistance and fruits matured earlier), less trouble with insects and diseases, and more beneficial organisms. His potato bug problem was gone.
Using a paramagnetic meter to measure a typical garden soil gives a reading of 8 to 10, said Fulford, while an active, minerally-charged soil will have a reading of 100 to 200. Adding a compost-rock mineral mix to the soil can produce a highly charged, productive, disease resistant soil.
Among the minerals Fulford has used are rock phosphate, greensand, granite meal and Azomite--a finely ground rock dust powder that has a high paramagnetic charge on it. "I eagerly buy about a pallet load a year and put it in my compost pile," said Fulford. He adds two or three 50-pound bags of rock powder per cubic yard of compost when he first builds the pile. Putting 25 to 30 pounds of this composted mineral matter around a mature fruit tree, at an expense of about $8 to $10 per tree, "is worth it for an heirloom tree, but not for a Mac or Red Delicious," joked Fulford. Rather than put the minerals in the compost, they can be scattered around the base of the tree, then the compost can be spread, then a couple of layers of cardboard can be applied "to buy time before the quackgrass comes through it." Using these methods, "you can get a crop three to four years earlier," said Fulford.
Greensand and rock phosphate can also be added in with the litter in animal bedding, and the animals will mix the materials together for you. Other ways to add minerals and rock dusts include:
You can contact Fulford about his consulting services at Box 151, Monroe ME 04951; Tel. 207-525-7761. For more about paramagnetism, see Paramagnetism: Rediscovering Natureís Secret Force of Growth, by Philip S. Callahan, 1995 and 1998, Acres USA.