Crop Comments: Thirty-nine months of carbon loss

This past February, Edward contacted me for help resolving some cropping issues — hopefully before the next growing season started. He runs an organic cash grain operation in western New York. His main crops are corn and soybeans. His biggest complaint was that the straight buckwheat stand he planted in 2019 — to give the land a break from corn and soybean — performed rather poorly. I asked him if he was able to plant winter forages (or cover crops) following the combining of these grains. By the time he gets his corn grain combined, he said it’s too late to plant anything else, and have it get a good start before winter sets in.

Next, I asked him if he had recent soil test results. He had nine test results from 2017, which he would send to me electronically. I told them that fields should be sampled at least once every three years. Thus, he should resample those fields before spring 2020 planting. He agreed to re-sample six of those nine fields, when the ground had thawed some, and get them analyzed at the Dairy One Lab in Ithaca (the same lab he used three years earlier).

In late March 2020, Edward was able to take those samples, get them air-dried, and sent to the lab in mid-April. The new test results appeared in my in-box on April 20. These brand-new figures let me compare such current values with data from January 2017. The “sorest thumb” sticking out was organic matter (OM). This is where I tell folks, “these are good numbers — you may not like them — but they’re good numbers”: His 2017 soil test results averaged 4.1% OM, and his 2020 results averaged 2.4% OM. Avoiding the percentage term, let me state that for every seven pounds of OM present in January 2017, only four of them remained in April 2020!!

Let’s put another face on this loss: OM is approximately 58% carbon. The other 42% consists of oxygen, hydrogen, and proteinaceous nitrogen — plus negatively charged anions (like nitrates, phosphates, and sulfates). With one acre, with a 6-inch deep topsoil layer, conveniently presumed to contain 1,000 tons of earth (2,000,000 pounds) for one percent of lost soil OM, the soil in question has released 11,600 pounds of carbon into the atmosphere (2,000,000 x 0.01 x 0.58). That lost carbon is mostly in the form of carbon dioxide (CO2), a greenhouse gas (GHG). Some of that dissipated carbon is in worse GHG form, namely methane. If that lost one percent of soil OM had avoided destruction, the resulting retention of 11,600 pounds of carbon would have increased that soil’s water reservoir benefit by 16,000 gallons. A little more math here shows Edward’s OM reduction of 1.7% (4.1% – 2.4%) reduced his soil water reservoir capacity by 27,200 gallons. He mentioned that his fields were taking their sweet time drying up. Apparently lost OM helps make mud even muddier. Reading between the lines even further, we can conclude that losing OM makes it even harder for soil to store nitrogen, phosphorus, and sulfur, since those elements — in their negatively charged forms — like to hang out in the soil’s OM fraction.

For Edward’s corn starter, I formulated a blend containing rock phosphate, Chilean nitrate (16-0-0), sulfate of potash, feather meal, blood meal, zinc sulfate, and boron. He is planting corn as I write [Tuesday (6/2/20) — once field conditions dried up enough — before they get wet again]. The fertilizer (or more correctly, soil amendment package) will be applied by PTO-spinner, as soon as corn emerges enough for rows to be quite visible. The soil is being fed — not the crop. When the corn is 6-8 inches tall, the field will receive its first row-cultivation, a process which, in addition to killing weeds, aerates the soil, giving the young plants much needed oxygen.

Once the corn is planted [a process which was delayed until soil temperature reached 50 degrees Fahrenheit (F)}, soybeans can be planted (assuming soil temperature hits, and stays at, 60 degrees F). Also in love with warm (60F+) soils are buckwheat (BW) and millets. One of Edward’s 2020-tested fields showed an OM of only 1.6%! So I recommended that he plant a blend of basically 17# BW, 33# millet, 3-4# clover per acre. Fertilize this with 150#/acre of rock phosphate.

This concoction gives symbiosis a good name. The allelopathic (natural weed-killing) nature of BW will discourage weeds — but somehow not the millet nor clover. The acidulation trait of BW will liberate bound phosphate (P) into the soil, as well as that nutrient complexed in the rock phosphate. The liberated P feeds the BW, the millet, and the clover. The clover fixes atmospheric N on its root nodules, thus forming nitrates for itself and its neighbors, BW and millet. This trio forms a huge amount of biomass. Some of the BW and millet will go to seed when they freeze to death; then the clover kicks into higher gear, before really cold weather forces it into dormancy. In dormancy, the clover survives the winter. Most of the BW and millet begins self-composting under the snow. Some of the still-standing members of these two summer annuals hang onto the snow. Come spring the clover will wake up, continuing to form nitrates for the next crop in the rotation — now, sensibly, corn. We should take another soil test when 2021 corn emerges in that field.

Edward and I talked about getting winter rye spun on the standing corn just before its too tall for a tractor to pass through with the last cultivation. He said he remembers when small aircraft would broadcast winter rye seed into standing corn, to give the winter grain a head start.

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