Soil Chemistry’s Invisible Dance
By TODD OPPENHEIMER
This sidebar is a supplement to The Drought Fighter
In a scattering of soil tests taken over the last two years, the nitrate levels in Kaiser’s fields have measured at an average of 50 parts per million (ppm)–twice the norm of 25 ppm. His phosphate levels are even higher—one measures 247 ppm. That’s roughly five times the level considered ecological by Ward Laboratories, of Kearny, Nebraska. (Ward Labs is one of the most advanced soil test labs in the country, and it’s where Kaiser tested his most recent samples.) “I would say that is extreme excess,” Ray Ward, the lab’s director, says, regarding the phosphate levels.
But here’s what really scared some of the soil scientists I spoke to: Kaiser gathers his soil samples in a fashion that is entirely different than the method recommended by soil testing laboratories.
Standard protocol calls for soil samples to be gathered from a field’s top 6 inches–to focus on where fertilizers are likely to be most intense. In some no-till systems, in fact, tests are gathered even shallower–at depths of 0-4 inches–because the lack of tilling is commonly believed to keep nutrients unmixed, and thus even closer to the surface. However, since Kaiser’s soil is so rich, he believes his nutrient profile runs deeper than most, and that the roots of his crops follow. So he generally gathers his soil at depths of 9-12 inches.
The difference this makes? “I don’t even know how to interpret that,” Thomas F. Morris, a Plant Sciences professor at the University of Connecticut who specializes in soil fertility, told me. “A sample is meaningless unless it’s taken at the depth recommended. If he’s measuring at nine to twelve inches, his nutrient levels would be two to three to four times higher at six inches. His phosphorus would probably measure at 500 to 700 ppm if he sampled properly.” Translation: The phosphates in Kaiser’s fields could be 10 times higher than they should be to keep water clean.
Then why aren’t these excesses showing up in Kaiser’s ponds? The answers fill in the final pieces of Kaiser’s nitrate-phosphate puzzle—at least, to the extent possible right now.
Both nitrate and phosphate, soil scientists say, often hide out in the soil. Nitrate can get buried inside the stomachs of soil microbes, becoming visible only when the bugs poop or die. Phosphorus hides in a different way—by clinging to soil particles, releasing over many decades as it slowly dissolves in rainwater. And sometimes both these nutrients, and the dozen or more others that are currently measurable, escape the tests altogether. This latter possibility is because Kaiser gathers his soil tests deeper than most–at 9-12 inches. Soil labs generally ask that samples be drawn from between 0-6 inches, because the upper layer is usually where nutrients are most intense.
Kaiser doesn’t follow the standard protocol because he believes it does not reflect the depth of his soil richness. That assertion is based on unconventional sampling tests, however, which really annoys traditional academic experts. “It’s disembodied data,” says Tim Hartz, a respected agronomist at U.C. Davis. Thomas Morris, a University of Connecticut professor of Plant Sciences who specializes in soil fertility, concurs. “I need real numbers,” he says, “I need a soil test that’s done in a way that’s proscribed by testing laboratories. Right now, he doesn’t understand the system. He’s operating blind.” Nonetheless, Morris thinks this much can be known right now: “It’s a leaky system. If he keeps this up for another seven years, there’s almost a 99 percent chance this will turn into an environmental disaster.”
Ray Ward, however, has an entirely different take. After reviewing the soil and water tests his lab performed on Kaiser’s samples, and considering them in light of the full scope of the farm’s operation, Ward began to suspect that Kaiser’s critics might be wrong. Part of what persuaded him was a single test, which drew soil at two depths from the same hole in Kaiser’s field. The test showed the concentrations of nutrients at 0-6 inches to be virtually the same as what could be seen deeper down, at 9-12 inches. Since this was a lone test–and one that contradicts what most traditional agronomists and soil scientists believe about how fertilization works–most were inclined to dismiss it. Yet it matches some intriguing recent studies that Ward has witnessed in Nebraska.
These studies compared fields worked with various kinds of tilling machinery against fields that aren’t tilled at all. After several years of cultivation, the researchers tested the soil in each of them at 2-inch increments, all the way down to 10 inches. To nearly everyone’s surprise, in the tilled fields, where the machinery vigorously turned and mixed the soil, the nutrients actually traveled downward more slowly than they did in the no-till fields, where no mixing occurred at all. The reason, the researchers concluded, is that in the no-till fields, where the soil was left undisturbed, a far greater multitude of soil microbes were able to develop. Those microbes then built tiny networks of roads and freeways throughout the soil, enabling them to transport nutrients more quickly and effectively than a plow can. “When you open up those pores with no-till,” Ward explains, “this stuff moves faster, because of the worm activity.” In other words, what is excessive in one environment may not be in another. “Paul has probably developed enough soil to hold these excesses,” Ward says. “He can do that now, because he’s still building organic matter. But he can’t keep building at this rate or eventually it’s going to spill out.”
Given Kaiser’s unusual circumstances, Ward isn’t concerned about his high nitrate levels (even at 40-55 ppm). But Kaiser’s phosphate numbers still worry him, and nearly everyone else I spoke with. And no wonder. In mid-January, 2015, 18 researchers reported in the journal Science that pollution from both phosphate and nitrate constitutes one of four changes wrought by human activity over the centuries that is now breaking the “planetary boundaries” that make the earth a safe place to live. If that’s not enough to worry you, using too much phosphorus fertilizer–a mistake that many farmers make–contributes to yet another looming problem: depletion of the world’s supplies of phosphorus supplements, all of which are mined.