Most U.S. agronomists agree on one major cause of global warming (or climate change if you prefer that term). That is the reduction of organic matter (OM) on U.S. cropland, arguably a greater issue than lost OM at any other farmed location on our planet. [Brazil may be a close second, as this equatorial nation keeps plowing up and/or burning more tropical rain forest]. The lower the OM level in our nation’s summer annual cropland (non-sod, basically corn and soybean), the lower the amount of carbon sequestered in our soils — and the lower the total plant biomass.
Reduced carbon in these two points of sequestration means that much more of this element is in the atmosphere as green-house gases. Reduced soil OM and reduced plant biomass also lower evaporative cooling capability. If we expand our understanding of OM, we encounter the term “humus”. According to sciencedaily.com, “humus is a complex organic substance resulting from the breakdown of plant material in a process called humification. This process can occur naturally in soil, or in the production of compost.” Take-home message here is that the more OM/humus your soils boast, the healthier they are. The very good news here is that growers can control the health of their soils. Soil health is the first crop production factor.
The bad news is that growers have basically no control over the other three main factors, namely solar radiation, temperature, and precipitation. Incoming solar radiation is abbreviated to “insolation”, a commodity measured in Langleys. A Langley is defined as one small calorie per square centimeter. Smog cover reduces the number of Langleys making it from the sun to earth. One can argue that this is a human-based control — and not a positive one. Temperature is measured in growing degree-days (GDDs). GDDs are a day’s average temperature in Fahrenheit (F), minus 50 degrees F. Thus, a day with an average temperature of 70 degrees F has accrued 20 GDDs. A “90-day corn” basically needs 1800 GDDs to mature. The GDD concept is pretty much corn-centered; note: it measures air temperature, not soil temperature. Soybeans, sorghums, sudangrasses, and millets want a soil temperature to be at least 60 degrees F prior to intense germination. Forage seedings and small grain plantings do just fine with 40 degree F soil temperatures, if the ground is dry enough, and Langleys are plentiful.
Precipitation is the fourth factor. Most crops grown in temperate regions (like our Northeast) greatly enjoy a stable monthly average of about three inches precipitation. Higher OM levels provide crops a lot of stability when rainfall comes with unpredictable timing. University of Texas agronomy research shows that when moisture is very short, sorghum can produce twice as much forage dry matter as corn can. We can’t control how much rain falls, but we can control how much gets stored for a non-rainy day. I extrapolated from some classic USDA data to show that that an acre of topsoil that has 2 percent OM can retain 32,000 gallons of water (about three quarts/square foot), while an acre with 8 percent OM can retain 128,000 gallons! This means that during a drought the higher OM soils, by using stored moisture, can continue performing, while nearby lower OM soils visibly parch. Conversely, when the floods come there’s significantly more resilience with the higher OM sods than with the lower OM annual row crops.
Tom Kilcer, a retired certified crop advisor, oversees field operations at the Cornell Valatie Research Farm. He addressed last year’s fledgling growing season in the May issue of his newsletter: “This season for the Northeast and Northcentral has one of the latest dates to start planting corn. Planting earlier would have made a muddy mess of the field, severely restricting yields all season. The cold and wet would probably have decimated the stand. So we waited and are now full-tilt planting corn. It is mid-May, shouldn’t we be worried about the hay crop, as we are usually starting mowing about now. The good news is that while the corn is going in late, the hay crop is also one of the latest I have seen in years.”
Tom didn’t predict it, but with a growing season start like what he described 10 months ago, it certainly didn’t surprise either of us that 2018’s season delivered the Northeast’s most mycotoxin-contaminated corn crop in many years.
Let me tap into Kilcer’s most recent, February 2019, newsletter. He titled this newsletter “Wet Soil Rotation Management.” His lead-in question read: “Why do we manage poorly drained soils like they are well drained?” Then he answers it himself: “This sounds like a dumb question, but it is very apropos. It happens on farms all across the Northeast and Midwest. Real farmers grow corn and alfalfa, so they do multiple years of corn. (This) makes drainage worse as the soil structure collapses and machinery compaction squeezes out what little porosity the soil originally had. In Canada, on silt soils, they now tile on 25 foot space as 50 foot no longer works because of compaction and over-worked soils.”
On a silty clay soil Kilcer performed an experiment last spring before planting. Quoting Kilcer, “We deep tilled on the only part of the farm dry enough to work in the spring. When we dug a hole, at 16 inches down we had liquid water that we could have pumped out.” Moisture sponged above in the soggy topsoil drained down to that hole.
Here are Kilcer’s preferred rotations, as he tries to get growers to refrain from soil-damaging long-term corn: “A 3 corn and 6 alfalfa over the 9-year life of the rotation on good soils will produce an average of 4.6 tons of dry matter/year. For less well-drained soils, two years of corn followed each year with winter forage, and then short three-year alfalfa or clover rotation will both improve the soil and the economic return.” Kilcer dislikes monoculture — he likes bare soils even less.