Knowing the Soil
Seasoned farmers can judge a soil at first glance, first touch, first taste. Dark means fertile. Loose and coarse-grained is appropriate for root crops like beets and potatoes. A "sour" taste indicates a low pH, well-suited to blueberries, for example.
My great-great-grandfather moved to this country, in the middle of his life of farming, from the marine province of Friesland in The Netherlands. Shortly after he arrived, he discovered soils in the northwestern corner of Michigan's lower peninsula that reminded him of the rich dirt of his homeland.
While visiting, he bagged a handful of that soil and then brought it home to his farm in southern Michigan. Everyone was offered a look. Maybe they fingered the dirt as well, or tried a pinch on their tongues. On the virtues of that bag of soil, he purchased 90 acres up north from a lumber company on contract. There my great-great-grandfather and his sons cleared the virgin hardwood forest to raise dairy cattle and establish potato fields, corn fields and cherry orchards that remain today, worked by my cousins.
Unlike the sandy loam of northwestern Michigan, the soil I dig in southwestern Wisconsin is dense and damp, dark as brownie dough. This is as much as I've learned from examining a handful. And in my first year of gardening this was all I cared about. But I knew that the more gardens I grew in that spot, the more I would be taking from the soil.
If we are what we eat, and what we eat derives from the soil, then we are of the soil. Depleting the soil's nutrients was akin to depriving my family of nourishment. I imagined a few years into the future, wan carrots, stunted peppers, and pale greens withering in their. But how does one know what the soil needs? I couldn't, by sight, touch or taste, have judged the soil's percentage of organic matter, nor the nitrogen and phosphorus content of what lay beneath that field newly scraped of its gargantuan goldenrod, wild parsnip and box elder saplings.
My neighbor to the north told me he's lived and farmed at "the home place" for fifty years. I asked whether he ever tested the soil. "Oh, now and then, I suppose," he said, but he didn't offer details, except that the pH was high compared to the more acidic soils typical of the area. He theorized that the adjoining road, which was topped with crushed limestone for a century before it was paved about 25 years ago, had caused enough lime run-off to keep the pH between 6.5 and 7.
He admitted to fertilizing his cornfields heavily with a basic nitrogen-phosphorus-potassium mix, but on his cash crop, tobacco, he would spread only the manure from his cattle.
"Frankly," he said, "I didn't see a need to test the soil much. It grew tobacco so well it had to be good."
Like much of our valley, the narrow plateau east of the river that has become my garden was once planted with short-season, cigar-wrap tobacco. It's a back-breaking crop. Older farmers of the region are bent like bucket handles from stooping over those rows at least thrice a season — in spring, to set the fragile seedlings; mid-summer, to snap off the budding tops; and late summer, to strip the leaves.
Until recently, when cheap imported tobacco flooded the market and the U.S. government ended price supports for the domestic crop, it was also one of the most lucrative. Now, it's more lucrative to collect what the government pays to not grow tobacco, and that is not a bad thing for the soil, either.
Tobacco exhausts the soil's nutrients — nitrogen, phosphorus, sulfur and especially, potassium. (This is partly due to farmers topping the plants, which prevents flowering and directs more energy to the leaves, resulting in a higher nicotine content.)
I decided to have my soil tested at the University of Wisconsin Soil and Forage Analysis Lab. But first I called to ask about the effects of tobacco-growing.
"When was it last grown there?" the soil scientist asked, and I guessed, based on local lore, that it had been two decades. "Oh, there won't be any effect. Maybe traces, a trace amount of chemicals left over, but probably not even that."
He wasn't concerned, then, about nutrient depletion. His comment referred to the methyl bromide farmers used to fumigate the soil before planting and the multiple applications of pesticide required during the growing season. Again he assured me, "But after decades, I'd say none of that is probably left."
Then he asked, "Was ginseng ever grown there?"
Ginseng ruins the soil forever, as far as agronomists can tell. In northern Wisconsin, acres once devoted to ginseng (another finicky and temporarily lucrative crop) are now worth one-sixth the going rate for agricultural land planted to anything else. "It's not an issue of soil fertility," he said. "You can add all the manure or commercial fertilizer you want, and still nothing will grow." Scientists have known about ginseng's effects on the soil for some thirty years, and yet they haven't identified the precise mechanism ginseng uses (perhaps a defensive toxin) to rid the land of competitors.
"No, just corn and tobacco," I repeated, and he gave me the usual advice: "Add manure."
The soil lab's sample submittal form requests your soil's name, which can be found online in the National Resources Conservation Service (NRCS) soil survey database. The map I retrieved for my property represented multiple soil types in bright colors, pieced together like the panes of a cathedral window atop a satellite photograph.
The federal government began amassing soil data systematically at the turn of the 19th century. Congress was persuaded by Milton Whitney, a Maryland agronomist and cigar lover — who claimed to be able to identify the soil in which his tobacco was grown by the flavor of the cigar — to survey the nation and to begin with soils of tobacco-growing lands.
Since then, the government has sampled every square mile of the country, mapping and naming over 20,000 soils. Early sampling was, of course, conducted manually. A USDA agent asked permission to walk your property, bored a metal auger into your dirt maybe a dozen times per field, marked each stop with a pinhole in the heavy paper of his field book and recorded his observations. Some agents set up small tables on tripods to sketch soil maps with colored pencils. Now the soil survey database is updated from the air, through satellite-based, digitized analyses of thermal, moisture, elevation, and vegetation patterns on the ground.
The soil of my garden is Fayette, named after Fayette, Iowa, and found in southwestern Wisconsin, southeastern Minnesota and northeastern Iowa. By name, one can know generally a soil's particle size and makeup, color, pH, water content, mineral composition, percent organic matter and dozens of other characteristics. According to the NRCS,"The Fayette series consists of very deep, well drained soils formed in loess."
Loess (which rhymes with "bus") is windblown silt, dust from the rocks the glaciers ground on their journeys south. Loess plus millennia of rotted organic matter make Fayette a silt loam, moderately acidic and very fertile. It's found on benches of land near rivers and before cultivation would have once supported a forest of oak and hickory. The State of Wisconsin declares Fayette "prime farmland."
I mailed two cups of Fayette in a Ziploc bag to the state lab and asked them to test levels of the trace elements calcium, magnesium, copper, zinc, boron, and sulfur, in addition to the standard organic matter, pH, phosphorus, potassium, and nitrogen. I waited two weeks for the results and then opened the envelope with the anticipation of a kid opening a report card. How did I do?
Most of the results did not surprise me. Potassium and nitrogen levels were somewhat low for growing vegetables. Organic matter was 2.4% and the pH was 6.5, high for the region, but ideal for a garden. And as other area farmers had warned, sulfur, calcium, and magnesium levels were well below the minimum necessary to grow plants high in nutrients and resistant to pests.
What was unusual, however, was the level of available phosphorus. At 75 parts per million (ppm), it was excessively high — triple the optimal amount and much higher than the state's average. Furthermore, according to the soil lab, average levels of phosphorus in the soils they tested between 1964 and 2004 had nearly doubled.
The reason? Continual fertilization. Phosphorus, along with nitrogen and potassium, is one of the key components of commercial fertilizers and manure. However, phosphorus doesn't disappear as readily as nitrogen and potassium. So the crops once grown on my soil had absorbed only a small fraction of the phosphorus added over the last century; the larger portion remains.
The detrimental effects of excessive phosphorus have to do mostly with runoff. If the phosphorus makes its way, through erosion or drainage, to ponds and lakes, it triggers algae blooms that suffocate fish and other fauna. On land, excessive phosphorus is less hazardous. However, it can imperil a garden's health as it bonds with minerals such as calcium and zinc, thus depriving plants of these essential nutrients.
With such high levels of phosphorus and so many trace elements to account for, perhaps the answer to bettering my soil wasn't as simple as "add manure," after all. I began to research alternative organic soil amendments — kelp, crab shells, fish guts, cottonseed meal, Peruvian bat guano — and soon became overwhelmed. None alone contained the right mix of nutrients, yet combining them, it seemed, would require the insight of a pharmacist dosing a patient, as the addition of one nutrient in excess could inhibit a plant's uptake of another. Some amendments adversely affected pH. Furthermore, I didn't know which additives were most effective and which, with their colorful labels and exotic names, were merely designed to appeal to new growers.
Late at night, I called a friend who farms a few miles up the road.
"Here's what you need to do," he said patiently. "Go to Cashton Farm Supply and ask for Ernie. Bring your soil report. You'll sit down with him in his rickety little office out back. He'll smoke a cigarette, look it over, tell you what you need. Then he'll mix up a custom batch of fifty pounds or whatever and deliver it to your place."
Sensing the reason for my quiet, my friend added, "He works with a lot of organic farmers, so that's no problem."
When I arrived at Cashton Farm Supply, Ernie was not in. I'd been warned that he's rarely in. Rumor had it that afternoon he was making a delivery to a nearby farm.
I stood in the small waiting area and examined the contents of a few shelves around its perimeter: bags of sunflower seeds and cracked corn for the birds, a revolving rack of greeting cards that featured watercolor country scenes, small bottles of teat conditioner and boxes of insecticide ear tags for dairy cows.
But these items, sparse and inconsequential, seemed to be there for exactly the purpose I found for them — diversion while waiting for Ernie. The real products, the huge bags of seed, feed and fertilizer, were in a long Quonset building behind the office, and they would be dispensed by Ernie.
In the next five minutes, three calls came for him. "No, not sure where he is. We're trying to track him down," the receptionist chirped. She paged him and called his cell phone twice. After a while, I left a copy of my soil report and a note, with faith that Ernie would eventually call, despite the relative triviality of my order compared to his regular customers.
A week later Ernie did call. He had just returned from an organic farming conference and was spending his first day back returning messages. He spoke with a smooth, low voice that, together with a barely perceptible speech impediment, made him sound like an east-coast mobster advising me on my first job.
"That soil's in good shape," he said admiringly. "It's obviously had a lot of manure put on it in the past." He wasn't at all concerned about the high phosphorus level. In fact, he told me I was lucky: "Phosphorus is the most expensive thing to add. That soil test was valuable for you. It saved you a lot of money."
His concern was the low level of potassium: "Potassium is responsible for the setting the seeds, for the seed bearing parts of the plants, which is mostly what we eat. Your garden probably looked good, nice and green, but you didn't get the yield you hoped for. Am I right?"
When I didn't answer immediately (what yield had I hoped for?), he continued, insisting that I add potash and debating the relative merits of different fertilizers.
In the end, he recommended 70 pounds of potash and 100 pounds of a compost-based fertilizer that, he said, contained a full level of trace elements. He calculated the total cost, less than $25.00, in his head. For him it was a simple business, and he seemed happy to help put an end to my confusion — and then ready to move to the next "While You Were Out" note.
Since my call with Ernie, I've worked the amendments into my soil and begun planting. I'm eager to see how this year's garden differs from last year's. Maybe the soybean aphids and flea beetles won't be as numerous, considering that pests prefer poorly nourished plants. Maybe yields will improve.
But, as grateful as I am to Ernie, my neighboring farmers, the USDA and the state soil lab for helping me assess the soil, in the long run, I would prefer to draw my own conclusions. After years of observation and patience, I hope to know my soil as well as my ancestors in Michigan and the farmers who preceded me on this land must have known theirs.
Maybe I'll taste it, even make a habit of tasting it, until I'm able to decide what its flavor means for the plants.