Right now is the best time to test your garden soil. But which "earth exam" should you give? MOTHER EARTH NEWS evaluates the best garden soil tests for 1985. (See the soil test chart in the image gallery.)
Point number one: While the best indicator of your garden soil's quality is how well your crops grow in it, a test of major chemical nutrients should provide a useful check on your plot's condition.
Point number two: The best time to test your soil is in the fall. Not only will any organic nutrients you add in response to the test results have time to decompose in the soil, but you'll be a whole lot more likely to get those results promptly. (You may have to wait six weeks or more to get a mail-ordered kit or audit in spring!)
Point number three: The test you should use is . . . uh, is . . . well, what is the best garden soil test? Have you ever wondered? We often have, so to try to satisfy our curiosity, we carefully unearthed a sample of Eco-Village garden soil—following all the recommended guidelines, such as taking the sample from several representative spots and being careful not to touch it with our hands or galvanized tools. Then we ran some of that sample through five different tests so that we—and you—could compare the results.
MOTHER EARTH NEWS evaluated the best garden soil tests for 2000. We used two do-it-yourself kits: the least expensive Sudbury model ($13.04 at our local nursery) and the LaMotte garden kit (model EL; $25.30 plus shipping from LaMotte Chemical, Chestertown, MD). We also sent off for three soil audits: one by our local agricultural extension service (available—at little or no cost—in most areas of the country) . . . a "standard audit" by Woods End Laboratory (Orchard Hill Rd., Temple, ME; $20.00) . . . and the "basic soil audit" by Necessary Trading Company (New Castle, VA; $19.50). Incidentally, if you decide to send a sample to either of the private labs, be sure to write for a questionnaire and sampling instructions before you do so.
And what did we find out for all our efforts?
The Best Soil Tests? That's a Good Question
The first thing we learned was that no two soil tests use the same language! Their testing procedures and rating systems vary, so you can't directly compare most of their results. For instance, look at our "Test Results" chart under potassium (K). Sudbury says we need 4% K . . . LaMotte says our K level is "very high" . . . the county ag service gives a free-floating "index" number, 286 ... Woods End tells us we've got 780 pounds per acre of the nutrient . . . and Necessary tallies our K at 500 parts per million! Uh, run that by us again?
Backup literature (or, in the case of the extension service, a friendly agent) tells how to interpret these results into low-to-high terms, though, so we did finally understand it all. We included those assessments in parentheses in the chart so you could interpret our feedback, too.
The next thing we learned was a bit more troublesome: The results don't always agree. Well, they all agree that our garden's pH is somewhere between 6.1 and 7.0 (a good plant-growing range), and that we have high levels of potassium and magnesium . . . but after that they range from "medium" to "quite high" on the same nutrient! Not surprisingly, then, the interpretations and recommendations vary, as well.
Sp What's it All Mean?
That's another good question. If you just look at our "Test Results" chart, you'll probably conclude that soil testers are like the proverbial blind men who each feel different parts of an elephant and therefore each decide it's a different creature. But that's not really a fair conclusion. For one thing, we weren't able to include all the detailed backup descriptions of each test in our five-in-one chart . . . and those often resolve some apparent differences. For example, although Woods End assesses our phosphorus (P) levels as "medium" and three of the other tests say it's "high," the company's full report states that, while our "available" level of P is on target, our "reserve" P level is 70 pounds per acre greater than desired. Woods End interprets the overall phosphorus data as "medium," but someone else could look at those same numbers and say they're high. Similarly, Woods End reports that our calcium level of 2,300 pounds per acre is "medium" (Necessary rates it "low"), yet also states that the desired level is 2,900 pounds per acre.
Several other times the interpretation of the data varied more than the data itself. Still, there were some real differences in the five replies. You just can't reconcile LaMotte's "medium" phosphorus rating with Necessary Trading Company's "quite high" one, for instance. And since the do-it-yourself kits involved assessing color variations of liquid in test tubes, those homespun results sometimes depended on who was reading them. Some people we showed that LaMotte phosphorus test to thought the liquid had a light blue tint, indicating a "medium low" level, while others thought the same tube was a darker, "medium"-rating blue.
Equally interesting were the various assessments of nitrogen. While the do-it-yourself kits quite confidently reported nitrogen levels, the results from the three services were much more equivocal. Both Woods End and Necessary admitted that their nitrogen numbers were made-up estimates based on such things as the amount and type of organic matter in the sample, while our local ag service didn't even pretend to be able to measure it there isn't even an N category on its form! Steve Rioch of Necessary explained the nitrogen problem to us: "The irony is that the nutrient that's commonly considered to be the most important one is also the one that's hardest to measure. Nitrogen's so variable depending on soil conditions and so volatile once taken from the ground that you really can't measure it except out in the field."
Quit Stalling: Which Soil Test is Best?
The principal conclusion we were able to draw from the variety of results we got may sound like a cop-out on our part, but we think it's actually quite important: The content of a soil test report depends on the philosophy of the tester. The two kit makers and the extension service apparently hold to the chemical theory of agriculture—the idea that the soil is little more than a medium to hold the plants' roots, so you have to add the specific chemicals that crops take out. Sudbury even gives its results in terms of how much of each nutrient you need to add . . . while the ag service people told us to add nitrogen to the soil even though they admitted complete ignorance of our soil's nitrogen levels! "Why?" we asked. "Because you're growing vegetables," they replied. (Incidentally, if you read our article "Preparing the Soil" in MOTHER N0. 93, you'll know how to substitute organic soil amendments for any recommended chemical ones.)
The people at Woods End seem to have a much more open-minded outlook. Like our gardeners, they clearly have an organic bias and are great believers in the virtues of compost (see their recommendation in the chart). Yet Robert Parties of Woods End told us they suggested compost partly because we told them on our audit questionnaire that the homemade amendment is our primary fertilizer. "If a gardener indicates that he or she always uses 10-10-10-type fertilizers, we'll give our advice in those terms. No sense in recommending something that won't be used." They also seem to run a surprisingly tolerant testing service. While noting that some of our readings were a bit off from ideal, their report doesn't suggest that such variations are cause for concern—a conclusion that's' bound to please anyone who doesn't think chemical analysis is the final word on soil assessment.
Necessary Trading Company seems to be taking a refined organic approach. As Steve Rioch said to us, "You have good fertility. What I'm trying to do is fine-tune your soil to help prevent pest outbreaks and nutritional imbalances in your crops." In our case, at least, such fine-tuning emphasized a balanced relationship between nutrients. Indeed, the words balance and imbalance appeared repeatedly in our report: e.g., "Your pH is out of balance primarily because of an imbalance between calcium, magnesium, and potassium." Necessary also placed special emphasis on the importance of calcium in the soil ("it may very well be the most important of all soil and plant elements") and on cation exchange capacity (and its balance). The latter refers to the number of calcium, magnesium, and potassium ions in the soil, ions that help the soil hold nutrients.
"The Percentage of Milliequivalents of the Reserve Value Index . . ."
Another distinction between the soil tests is how easy or difficult they are for the gardener to understand and follow. The worst report in this category was the one from our agricultural extension service: It was clearly geared to the commercial chemical farmer (or the closet chemist!) and was quite intimidating. On the other hand, our local agent was readily available to explain the results in lay terms (and the test was free!).
The LaMotte and Sudbury size-ups were easier to understand than the county ag's, and both companies provided useful explanatory booklets about soil and fertilizers. (The kits also give you the capability of repeating your tests more than a dozen times.) LaMotte's literature was the more complete of the two—and its kit a good bit easier to use. It was also more sophisticated; some of the LaMotte tests required twice as many steps as the equivalent Sudbury ones.
The Woods End and Necessary reports were both a pleasure to read. Woods End comes with a personal, down-to-earth overview of the results. (Ours included the flattering statement, "I hope you are not having problems with the soil, because I would be hard put to offer any help.") The full report was easy to digest and the enclosed discussion of terms a definite help to anyone who ever slept through part of chemistry class.
Necessary managed to provide the most thorough report of all, while presenting its analysis in a clear and understandable manner. Since its audit questionnaire was also the most thorough—including questions on predominant weeds and persistent bug problems—its recommendation sheet covered areas the others didn't address ("sprinkle diatomaceous earth for slugs"). The additional three-page, detailed report explained the role of each nutrient and the effect of any problem with our levels. (Necessary also offers a 42 page booklet, called "What Makes My Garden Grow," with each test.)
What We'll Do
So now that we've been blessed with an array of agricultural assessments, just what are we going to do in our garden? Well, if our comparisons make nothing else clear, they certainly show that a soil test is just one gardening tool, not the answer, so we'll combine the data gleaned from the tests with our own experience with the soil and the crops at the Eco-Village. And since we're ardent organic growers who believe in cultivating healthy soil first and foremost ("feed the soil, not the plant," the saying goes), we'll give more weight ourselves to the Woods End and Necessary reports. Susan Glaese, our head gardener, says, "I figure our soil deserves about a `three-star' rating. It's definitely not a 10-10-10 wasteland, but it's not growing Findhorn-size cabbages, either. I agree with Necessary that our humus levels are too low, but that's because in the past we've had to spread our compost over 130 raised beds! I've made the garden smaller now, so I should be able to use more compost in each growing area. And I think I'll follow Necessary's recommendations for increasing our calcium levels and avoiding additional potassium it'll be interesting to watch the garden over the next year and see if such measures make any difference in our crops."
But What Should You Do?
One thing for sure: Don't get five soil tests! It's a bear to sort them all out . . . and hard to deal with their contradictions. Instead, we'd recommend that—if you choose to test your soil at all—you pick the approach that suits your own gardening philosophy. If (perish the thought) you'd like to sprinkle an N-P-K formulation on your plot and be done with it, go with one of the first three tests we used. If the organic approaches of the "moderate" Woods End or "balancing" Necessary audits sound like your cup of (manure) tea, pick one of those—both companies were impressively helpful and informative.
Most important, whichever test you pick, don't automatically believe everything it tells you. Heck, even professional soil testers will admit that what we don't know about soil is a whole lot greater than what we do. So let your own eyes, hands, and crops be the final authorities on the state of your soil.
Sizing Up Your Soil
Bill Wolf of Necessary Trading Company gave us these suggestions for non-chemically assessing the state of the soil:
 Organic matter: If your soil has a high humus level, it should look dark and have an appealing "earthy" smell.
 Texture: Roll a handful of medium dry soil into a ball. If it holds its shape, you've got a substantial amount of clay in your soil . . . and if you can further roll the ball into a "sausage, " you've got a lot of clay.
If you can make scratches on the surface of your clod, it's got a significant sand content, but if it feels somewhat greasy in your hand, your soil's got a fair amount of silt. If that handful crumbles when you try to ball it up, your soil has a nice, balanced texture.
 Root development: Dig a hole two feet deep in your garden and examine it to see where your plants' roots are. If they're going down the full two feet, your soil is fairly friable. If they run lateral at some point, though, you've got a compacted layer—plowpan or hardpan—that needs to be broken up.
 Drainage: Now fill that hole with water. The liquid should slowly percolate out into the surrounding soil. If it stays pooled at any level, you have a drainage problem.
 Soil fauna: Pick a day when your garden is somewhat moist, dig up an exact 1 inch by 1 foot by 1 foot section of soil, sift through this cubic foot, and count the number of earthworms you find (they'll serve as barometers of all kinds of soil fauna). Ten or more is a good sign of soil life; zero is terrible.
 Nitrogen facing: Dig up the roots of some legumes—beans, peas, alfalfa, clover—and examine them for nodules. Break a few of those root lumps open. If they're fixing and storing nitrogen as they should be, they'll be pink inside.
Several garden weeds can give you indications of your soil's condition:
Fertile soil: lamb's-quarter, chicory, purslane,
burdock, and dandelion.
Soil with low fertility: fennel, sorrel, mayweed, and chamomile.
Soil with a crust or hardpan problem: horse nettle, morning glory, quack grass, chamomile, field mustard, pineapple weed, and pennycress.
Soil with poor drainage: hedge bindweed, smartweed, white avens.
Acid soil: dock, horsetail, hawkweed, sorrel, lady's thumb.
Salty soil: sea plantain, sea aster, Russian thistle, shepherd's purse.
"Seeing" Nutrient Deficiencies
We asked our friend Don North, an area nurseryman, horticultural consultant, and native plant propagator, to describe the common nutrient deficiency symptoms of garden crops. Don told us that, in general, tomato plants are especially good "deficiency meters" and then listed the shortage symptoms he most often sees:
Nitrogen: Many deficiencies, including nitrogen, show up as chlorosis, a yellowing of leaves. N shortage, though, appears mostly in the older leaves (the young ones hog the available nitrogen) at the bottom of the plant. These yellow and "fire" (get a burnt look). The entire plant may also be stunted.
Iron: The veins keep their green color in iron-deficient plants, but the rest of the leaves yellow or turn light green. (Don's remedy? Iron chelate.)
Sulfur: In this case, the young leaves (including veins) turn chlorotic.
Potassium: K-short crops exhibit yellow streaking, along with curling, mottling, or spotting of older leaves. The plants are often particularly disease-susceptible.
Phosphorus: Plants low in phosphorus are often small, have very dark green or bluish foliage, and red or purplish veins. Poor fruit development is another indication of P deprivation.
Calcium: The classic sign of calcium deficiency in tomatoes is blossom-end rot. Other symptoms are hard to spot: Young leaves and terminal buds may become hooked in appearance or die back at their tops, or the young leaves may remain folded or look wrinkled. (Don recommends Viking brand calcium nitrate—from Norway—for both calcium and nitrogen shortages: "It's one of the best fertilizers around. ")
Boron: If your broccoli and cauliflower stems are soft and brown in the center, your soil's got a boron deficiency.
Soil Test Results for Mother's Eco-Village Garden