Crop Comments: Rubik cubes under foot

Recently, Thomas called me with some questions regarding soil tests results coming from five fields which he had sampled in late-June. On all the fields the soil type was primarily Mardin silt loam. According to the website https://soilseries.sc.egov.usda.gov, “The Mardin series consists of very deep, moderately well-drained soils on glaciated uplands, mostly on broad hilltops, shoulder slopes and backslopes. These soils formed in loamy till, and have a dense fragipan that starts at a depth of 14 to 26 inches below the soil surface.”

I lump Mardin in the category of soils that offer the crop person the advantage of not being able to get away with sloppy practices. In other words, Mardins have to be managed.

Thomas borrowed one of my soil augurs and brought me the soil samples, which I air-dried, then thoroughly screened. I mailed the five samples to Dairy One Lab in Ithaca. They were received on June 26. With incoming sample volume past peak, the tests were performed promptly, with the results being e-mailed two days later. The results did not surprise me. The predominance of goldenrod and curly dock had pretty well foretold what showed up on paper: all five soil test results showed pH in the 5.2-5.5 range. Phosphorus levels were all very low. Potash levels ranged from low to medium. And base saturation percentages (BSPs) for magnesium (Mg) ranged between 4.4 and 7.7 percent. To most agronomists (myself included) these low Mg BSPs mean that the limestone should be dolomitic (high magnesium).

Even before we got the test results back — since he wanted to plant a balage hay crop for his small beef herd — I recommended Japanese millet. Of the summer annuals, the millets are (in my opinion) most tolerant of less desirable growing conditions, with Japanese being the most forgiving. On a seven-acre piece I recommended that he plant straight millet at a generous seeding rate of 50 pounds per acre. The soil test called for 1.5 tons of ground limestone rated at 100 percent ENV (effective neutralizing value). Thomas said the limestone he would procure was 80 percent ENV. This meant the actual amount applied per acre should be 1.875 tons. The ground limestone arrived in early July and was spread at the correct rate on most of these five fields, including the ones where millet would be planted. On another piece — this one three acres — I recommended that Thomas plant a blend of millet and buckwheat: 50 pounds of buckwheat mixed with 100 pounds of millet, drilled-seeded. So each acre receives approximately 17 pounds of buckwheat and 33 pounds of millet. Buckwheat is unusually tolerant of poor fertility, including low pH. With its allelopathy properties, buckwheat fends off most weeds; fortunately, it doesn’t appear to consider millet an enemy. Buckwheat’s acidulation trait enables it to secrete mild acids from its roots to liberate complex nutrients (particularly phosphates), that it can “ingest” as well as share with a companion crop — and the next crop in the rotation. Understand, the phosphorus thus mobilized must be replaced — and sooner rather than later.

On July 20 I helped Thomas calibrate his antiquated John Deere Van Brunt grain drill. By studying the still-legible charts on this implement we were able to determine the correct gear setting, so as to drop the 50-pound rate per acre. I double-checked that accuracy by calculating the circumference of the seven-acre piece. With the field in question roughly twice as long as wide, a calculated 1900-foot field circumference — combined with a 10-foot wide grain drill — meant that the first pass seeded 19,000 square feet, or 0.44 acres. So Thomas and I looked at the small grain seed hopper and agreed that we had dropped about 22 pounds of millet seed. As we used to say in Cooperative Extension: sometimes you measure with a micrometer, then cut with a hatchet. A day later, Thomas successfully planted the buckwheat/millet blend all by himself.

The main question he called about dealt with the term CEC on his soil tests. I told him that CEC means cation exchange capacity; that cations are positively charged element forms. On his five soil tests, CECs ranged from 7.6 to 8.8 milli-equivalents per 100 grams; without getting too fancy, just accept that these numbers are on the low side of normal. I told him that CEC can be best thought of as a production site where the microscopic biochemical plant food building basics take place. And that these sites are three-dimensional. So I likened the CEC concept to the brain-teaser toy Rubik’s Cube.

Without explaining exactly how the game is played, each side of a 3x3x3 cube has nine squares; since all cubes have six sides, the 3x3x3 would display 54 squares worth of surface area. The 4x4x4 Rubik Cube, with six sides — and 16 squares per side, boasts total surface area of 96 squares. There is also a 2x2x2 Rubik Cube (much more my speed); each side has only four squares, resulting in that cube’s total surface area equaling 24 squares. Volume-wise, eight of those 2x2x2 cubes would fit in one 4x4x4. Total surface area of those eight smaller cubes equals 192 squares. Punch line to the joke: the smaller the cube, the greater its surface-to-mass area. This concept applies to soil particles: the smaller their size, the greater their surface area to mass ratio — and thus their CEC production site.

USDA data define sand particles as having diameters in the 0.05-2.0 millimeter range; silt particles have diameters in the 0.002-.05 millimeter range: and clays are less than .002 millimeters in diameter. Some of the most productive soils are clays with high organic matter, and good depth (at least 30 inches) to fragipan. Their CECs can approach 30!

2018-08-07T07:30:20+00:00August 7th, 2018|Eastern Edition, Western Edition|0 Comments

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