|Cornell Soil Test Report.|
Bianca Moebius-Clune, a graduate student at Cornell University, introduced the Cornell Soil Health Test (CSHT) at the 2008 Farmer-to-Farmer Conference, and Dennis King of King Hill Farm in Penobscot, Maine, told how he evaluates soil health on the diversified farm that he and Jo Barrett own and run.
Soil health is the ability of the soil to function physically, chemically and biologically so that crops can grow and soils resist degradation, said Moebius-Clune. Soil chemistry – the pH, N, P, K, etc., measured in most soil tests and useful for organic farmers to know to some extent – is well understood. Physical aspects of the soil are well understood but are barely applied in soil testing. A healthy soil, for example, will resist damage during flooding by having stable aggregates, but most soil tests do not measure aggregation.
Biological aspects of soils are less well understood, yet soil life drives the system. For example, when organic matter is added to soil, biological activity increases, which results in some decomposition, leading to detoxifying harmful substances, releasing nutrients, building humus and other growth promoting substances, increasing aggregation, improving pore structure and soil tilth, and often reducing soilborne diseases and parasitic nematodes – all resulting in healthy crops. A healthy soil balances many functions, and the CSHT measures that balance… or imbalance.
New York growers report increasing susceptibility of soils to drought with resultant poor crop growth, or “Sick Soil Syndrome,” said Moebius-Clune. “With that you get increased pest outbreaks and other biological and physical problems. With decreasing soil health, people are having to use more inputs, to get the same or lower yields.”
The CSHT increases awareness of soil health and determines constraints, whether compaction, low organic matter, insufficient pore space or others, and recommends improved management techniques. It also helps researchers study soil management; and it can help those considering buying land.
The CSHT has been available for two years. For $45 per sample in 2008, it measures 13 indicators in the lab and two in the field. The test is optimized for spring sampling, because many aspects of soils change over the seasons, and sampling at the same time each year improves interpretation of the results. The indicators measured are sensitive to management; can be measured reproducibly; are easy for the public to sample; and are inexpensive to run in the lab.
Those indicators are:
- Aggregate stability – the ability of soil crumbs to hold together
- Available water holding capacity
- Soil strength – how hard the soil is at the surface and subsurface
- Texture and stone content
- Organic matter content
- Active carbon content – the “dead” organic matter (as opposed to the living and the very dead) that is highly available for microbes
- Potentially mineralizable N – the potential of the soil microbial community to produce N from the organic matter (OM) fraction
- Root rot rate
- The standard nutrient analyses
Soils are sampled at five points by taking uniform slices from 0 to 6 inches deep, and the slices are mixed in a bucket. The uniform slice is important, especially for measuring the biota that live in different zones – e.g., at the soil surface, down 4 to 5 cm, or deeper. The sample must be kept cool to preserve this life. About 6 cups of soil are sent to the lab, along with a form that includes penetrometer measurements of soil compaction.
To measure aggregate stability, the lab simulates a controlled rainfall over a soil sample on a sieve. The percent of soil (on a dry weight basis) remaining on the sieve after this “thunderstorm” is the measure of aggregate stability. “If you’re only getting 5% stable soil aggregates, that’s not so good,” said Moebius-Clune.
Available water capacity is measured by seeing how much water remains in the soil under various amounts of pressure.
To measure the potential for N to be mineralized from OM, available N is measured before and after the soil is incubated anaerobically for seven days.
Active carbon is measured by adding permanganate to a soil-water suspension. The more active carbon, the less purple the soil extract becomes. This factor is measured by light absorbance.
To measure root rot potential, beans, which are highly susceptible to disease, are grown in the soil for five or six weeks, then the roots are rinsed and rated from 1 (very good – white, fibrous, healthy looking roots) to 9 (very diseased roots).
All 15 indicators get a 1 to 10 rating. For example, a pH of 6.6 rates 10; 5.4 rates 1. Aggregate stability is not so well studied, so, after testing thousands of soils, samples are now rated according to percentile distributions for N.Y. state farms.
Then each measure is color coded on the report sent to growers. Green means good; red indicates a problem; yellow suggests caution. So a glance at a test report tells how good (green) or bad (red) the soil is overall. Another part of the report lists constraints of the soil.
An overall quality score is based on a possible 100 points. On one soil that tested 58.8, for example, “You want to do a lot of work,” said Moebius-Clune; another, at 81.7, “is pretty good.”
In looking at thousands of New York soil samples, Cornell researchers noticed issues with aggregation where vegetable crops had been grown for years (mostly using conventional methods), because of so much tillage. Many diseases followed. One conventional farm had virtually no aggregate stability, while a long-term organic farm had 70% aggregate stability – among the highest in the database. “You can till, as long as you’re putting enough organic matter back in,” said Moebius-Clune.
Aggregate stability on an organic farm with permanent beds that are never tilled but are mulched and get an inch of compost added per year was almost 85%. This grower sees little disease in his crops. Other measures were also very good on this farm – except for phosphorus (P), which was getting too high because cow manure was added every year.
The CSHT can help growers think about ways to improve their farms. Depending on constraints and on available resources, growers may choose to change management by reducing tillage, rotating crops, growing cover crops or other practices. Different management approaches can mitigate any particular problem, and individual management practices can mitigate more than one problem. Adding manure, for example, improves aggregation, adds OM and active carbon, increases nutrients in the soil, and more. This differs from the traditional soil test, which just tells which materials to apply.
Indicators are sometimes related. For example, high OM is often associated with high mineralizable nitrogen – but potentially mineralizable nitrogen could be low, for example, if soil microbes are not well equipped to produce plant-available N from that OM. Stable aggregation is possible even with relatively low OM. Total soil OM changes slowly, so you may have high active carbon but low OM if you have just started adding organic matter.
One soil health report isn’t a sign that one farmer is “better” than another, because farms differ so much in their histories, management, soil types, etc. A recently established organic CSA farm that previously grew corn with repeated moldboard plowing and had soils containing 80% sand may be well managed now but should not be compared with an organic farm with better soil texture and a less abusive history.
Moebius-Clune noted that soil texture influences the interpretation of some test results. For example, “a sand that has an aggregate stability of about 30% is really pretty good, whereas a clay at 30% is really bad.” And “clay holds water in smaller pores than sand does, and a loam is especially good at holding a large amount of plant-available water. No matter how well you manage [a sandy soil], it Available Water Capacity is not going to make it to the same point of a loamy, perfect soil texture.”
The CSHT can be done without the penetrometer measure. Moebius-Clune noted that growers could simply push a metal stake into the ground to test for compaction. “Especially with subsurface compaction, you can usually tell where your plow compaction is. You’ll push in your stake and it will go and it will go, and suddenly you won’t be able to push it any further if it’s really hard. Or suddenly you’ll break through and it will be soft under that.” If you moldboard plow to a depth of 8 inches regularly and you detect a plow layer, she suggested setting a subsoiler to go an inch or two below where that layer stops, and going through the field once or twice (criss-crossed). After breaking up the plow pan, use cover crops or other management tools to keep the soil in good shape.
One participant noted that gypsum (calcium sulfate) can break down compaction. Another suggested growing sweet clover for two years, but plowing it down before it goes to seed the second year; and alfalfa, which also puts down a long taproot. King said that he only moldboard plows sod, and then he doesn’t repeat that until he has sod to plow down again, in six to eight years. He added that frost also helps break up compaction.
Moebius-Clune suggested getting an initial soil health test and then testing again three or five years later to see if management changes made after the first test had any effects. Those changes (covered in the manual) might include reducing tillage, minimizing compaction, adding OM or rotating with cover crops. For example, with low aggregate stability, you might include a cover crop to feed microbes that secrete “glues” that hold aggregates together; and you can reduce tillage. Cornell’s cover crop decision tool at allows you to pick a management goal, a planting time, and the time available in the field; the tool then lists the best cover crops and planting information for that situation.
Cornell continues to work with many growers to refine its soil health test and its cover crop decision tool. Soil samples are accepted between about mid-April and late June. Most come from New York, but growers from other states are welcome to send samples. Results are available in about two months. The researchers plan to have regional databases eventually, to help them interpret tests better.
“What we’re really looking for is healthy food,” said Dennis King, “and I do measure that.
“The first thing that I think is important for soil health is diversity,” he continued. King Hill Farm raises livestock, hay, balage, grain, pasture and about 2 acres of vegetables per year with an eight-year rotation. “The thing I get the most bang out of is taking blueberry land and making it grow alfalfa” – which King has been doing on his once stony, overgrown farm since the ‘70s. By using practices including topdressing with nutrients and grazing cows and sheep, he converted land “from Scotland to Ireland,” as one friend said. Now some 12 acres of old blueberry land is permanent pasture.
King and Barrett keep 30 ewes and sell freezer lambs. They winter sheep and cows on opposite sides of a barn on concrete pads with deep beds for about five months, later making some 200 yards of compost from the manure-bedding mix. After diversity, said King, compost is most important for soil health.
The farm doesn’t import much feed but grows wheat, oats and barley for feed grain. King does buy 1 ton of soybeans every year and a half.
The lush, beautiful legumes growing on the farm are one measure of soil health. He makes one cutting of hay on some 10 acres of land, then puts lambs and young beef cattle there. King likes to leave the last cutting of a legume on the field to die and decompose.
King flushes sheep on brassica pastures, which increased lambing by almost one lamb per ewe. He plants 60-day ‘Burket’ stubble turnip on Aug. 1, before weeds have gone to seed; puts ewes on it on Oct. 1 and rams on Oct. 20. Sheep immediately eat the pigweed and lambsquarters, before they go to seed. “You get far more feed out of 90-day brassicas, but the weeds have a chance to go to seed,” said King. He brings fattened sheep off the brassicas the day before the first big snowstorm.
He grazes animals together: “Sheep can go through and eat every blade of grass and never eat a seedhead. Cows don’t have that ability; they’re just mowing machines, so I get a lot better grazing with sheep and cows together.” As soon as carrots are pulled, animals graze the whole farm, including vegetable remains. “I don’t let them on an alfalfa stand until we’ve had really hard freezes. I’ve read that alfalfa needs the month of September to develop root reserves. Snowless winters can kill a lot of alfalfa or clover.”
Mulching between rows of vegetables growing on black plastic helps the soil. “The next year the biology under that mulch seems to be really good and [the soil] has beautiful structure.” He also cover crops with a PVO (peas-vetch-oats) mix and thinks that a year’s rest in PVO increases the biological activity in a soil. “PVO is amazing; it can take a poor field, and the next year it doesn’t even look the same. Wild turkeys and deer like it, too.”
On one new field, he grew PVO for a whole season; the following year he summer fallowed the land, then grew forage brassicas to kill perennial grasses and reduce weeds. Sheep foraged on the brassicas, and the next spring, King quickly weeded then planted a grain undersown with a legume, leaving that for three seasons. This is typical of his six-field farm and six-year (or longer) rotation. He added nutrients twice during the six years, based on soil tests.
King likes to have at least five kinds of seed in his pasture mix but is careful not to put too much red clover with alfalfa, because clover can dominate alfalfa. “I have had times when I’ve just put 2 or 3 pounds of red clover in with 5 to 8 pounds of alfalfa, and in two years I can’t find a single sprig of alfalfa.”
Kinsey’s Soil Test
King uses Neal Kinsey (www.kinseyag.com), a William Albrecht disciple, for his soil chemical analyses. “He’s really fussy about keeping proper cation ratios,” said King, suggesting a ratio of 68% base saturation of calcium, 12% magnesium, and about 5% potassium. Kinsey charges $50 for first test and $35 after that. (The UMaine soil test is $12.) The old Dragon lime from Thomaston gave King’s soil the perfect ratio of Ca to Mg. “Now all the lime you can get is higher in magnesium. You don’t want magnesium up to 20 – that makes soil hard and sticky.”
The UMaine soil test didn’t show changes in the phosphorus (P) content of his soil, even though King added about 3 tons per acre of colloidal P over the years. Kinsey’s test, however, shows that a lot of that land has too much P. Different labs use different extraction methods and give different results. Kinsey measures total reserve P, and because that’s so high in King’s soil, Kinsey says not to apply compost or manure. King sometimes breaks this rule, but last year he put 500 pounds of fish meal on the vegetable plot instead of compost and didn’t see any difference in crop growth.
Kinsey gives micronutrient recommendations, always suggesting that King add iron, which he doesn’t, because our soils have abundant iron. He does apply copper, zinc and boron and believes that those nutrients “really improved the flavor of our vegetables” after a year.
Sometimes, based on Mg levels, Kinsey recommends Sul-Po-Mag or potassium sulfate. “In my hayfield, I have a hard time keeping the K levels up. If you don’t keep K levels up, you won’t have healthy legumes.” King tests soil only once or twice per rotation or when he’s going to add nutrients. His nutrient mix is made by Northeast Ag Sales in Detroit, Maine (1-800-462-7672), based on Kinsey’s recommendations.
Brix, measured with a refractometer, tells the sugar content of plant sap. “Acres eco-consultants say if you can keep your plant sap at 12 or above, you don’t have any insect or disease problems,” King explained. “It’s really hard to get that high and keep it that high.”
Last year, the lowest Brix in his balage occurred in grass stems (12) and leaves (15) from the first cutting; the second cutting measured 15 to 20. “We could have put one of those bales in the back room and lived on that 20-brix stuff,” King joked. “It was kind of alfalfa sauerkraut.” His carrots measure about 10 Brix – “good but not excellent.”
King makes 200 yards of compost with the bedding from his barn, adding old waste hay because the balage is so moist. He makes 200-foot-long windrows in the spring, spending at least two hours making each windrow with his tractor and leaving a foot or two between windrows. A compost turner shared with Paul Birdsall has paid for itself, as it turns one windrow in about 15 minutes. Tractor-operated turners cost half as much as the stand-alone model, but King didn’t have a tractor with a low enough transmission to run a turner when he bought his. His turner handles the long plant material from balage well. He had worried that balage – a fermented product – and the fermented manure on the pads wouldn’t make aerobic compost, but that hasn’t been a problem. He turns piles about 10 times. When the material peaks at 130 degrees, he turns it every other day for about two weeks. Once the temperature drops to 100, he turns it once a week. He pushes the compost into a pile in the winter to reduce leaching.
He spreads about 20 yards of compost per acre on forage brassicas and about 16 yards per acre on vegetables, which are on the plot for only two years; he doesn’t apply any compost when grain crops are grown. King noted that by planting early enough and densely enough to suppress weeds (but not so densely that plants lodge), he hasn’t had many weeds in his grain crop.
The first time you put compost on a field, you probably can’t put too much on, said King. “But if you’ve got a field you’ve farmed for 20 years, and you’re still putting 20 yards per acre on it yearly, that would be way overdoing it. Even at my 8 yards to the acre, once I run the disc over a field I’ve put compost on, you can’t see it anymore. It’s such a thin layer.
Nicolas Lindholm recommended the book From the Soil Up to help with interpreting soil test results. Lisa Turner said that the $12 UMaine test is most economical for her as she tests often and in many spots while bringing pH 4.5 soil up to grow vegetables, and as she tracks the pH of her greenhouse soils. She adjusts a 6.2 soil up to 6.5, because otherwise, “I know I’m going to be dropping and heading down, and when I’ve [raised the pH], things have grown better.” King said that most of his fields needed 5 to 6 tons of lime to begin with, but, maybe because he’s been easy on the land farming it, “once I’ve got the calcium, magnesium, pH where they’re supposed to be, I’ve got fields where I haven’t put any [lime] on for 30 years.” Turner said her soil pH will go up, then it drops, then it goes up again and stays, “but I get that drop at about two or three years, then I can hold it.” Extension educator Mark Hutchinson said that’s partly due to the buffering capacity of compost. Initial lime additions will raise the pH, but as the soil has more OM, its buffering capacity increases, so fluctuations are less likely. Moebius-Clune said that soils differ in exchangeable acidity. “For some soils, you might have to add lime over 10 years, for some you only need to add it once or twice.” Hutchinson stressed the importance of accumulating soil test results over time; one soil test will not tell how to manage your soil.
One participant said that if soil cations are balanced, the pH will take care of itself. Others cited charts showing that nutrient availability changes at different pH levels, so these growers address pH first.
Moebius-Clune said that adding OM to the soil, among other benefits, increases its buffering capacity, by for example creating more places for hydrogen ions (which cause acidity) to bind instead of remaining in the soil solution. Different soil functions are interrelated, she added, so changing one thing will likely affect many others. “Some things are easier to change than others. You have to look at all of your soil constraints so you can effectively decide how to change management.”
– Jean English