Written by Anna Cates on Tuesday, December 06, 2016 at 4:05 PM
This is a most revealing time of year to drive through agricultural country. While high summer is a vast sea of green, at this time of year the golds, tans, browns and occasional greens tell us not only what crop grew last season but a little about how some one manages their soil.
Broadly, the more residue left on the field, the less vulnerable it is to soil erosion. The residue can be a thick, chunky yellow carpet of corn stalks and leaves left by the combine- that’s about the brightest hue on the hills. If the 2016 crop was soy, the residue is generally a washed-out gray, and there’s a lot less of it than corn. Some farmers will bale most of the stalks and leaves of corn after harvesting grain, leaving only the rows of short stalks on the field. Some will plow the residue in, leaving a smattering of yellow flecks through the choppy dark earth, and sometimes farmers strip-till, leaving long, dark stripes where corn or soy will be planted next spring.
I cringe a little when I see fields plowed up in the fall, because the plowing speeds up decomposition of that residue by exposing it to air and microbes. That usually means less soil organic matter. But there’s plenty of good reason to fall plow: slow decomposition of residue may tie up nutrients that next year’s corn could use, manure may need to be incorporated, and the soil will warm more quickly in the spring, so that it’s dry enough to plant corn or soy nice and early and the seeds germinate comfortably in a warm seedbed. If the spring is wet (common enough), it can be hard to find a dry window to plow and a second window to plant. Maybe putting off plowing until a wet spring would actually lead to more soil compaction because of all those tractor passes on wet soil, which is more vulnerable to compaction. Or maybe farmers are susceptible to that deep open feeling that a field of moist dark turned-over soil gives us: there’s so much potential there. When I see the deep black squares on the landscape, my scientist brain winces but I also feel the satisfaction of pioneer settlers settling happily in for the winter.
Green is about the last color you see on the Wisconsin agricultural landscape this time of year, but it’s my favorite. There’s the yellowy green of grazed pastures or hayfields going dormant, the rich green of an alfalfa stand that’s had a long time to regrow this warm fall, and the fresh bright green of cover crops in long tiny rows against black earth. These green spots are contributing living plant residue to that soil organic matter, stimulating microbial growth and cycling nutrients. The perennial pastures and hayfields are almost never vulnerable to erosion or compaction, because living roots sustain soil structure.
I like to imagine the decisions behind the patchwork quilt of dull colors on the hillsides. Did that area get a cover crop because corn was harvested earlier there, so the farmer had time? Or because it’s more productive and so the farmer could afford cover crop seed? How old is that alfalfa stand and how many more years will it be around? Why plow that side of the road and not this side? Besides the view, the outcomes of these personal decisions made on private land have an effect on public goods like water quality and long-term sustainability of our soil resource. We all get to see the final decisions spread out along the highways, but the dynamics of each one are hidden, and probably as various as the tawny colors themselves.