Back in 2005… while I substitute-taught the ag program at the local vocational school… a student got a lesson in soil compaction. (I liked it when someone grew tomatoes, particularly when they ripened during the dead of winter.) One student was watering his little elevated garden plot, using a pretty intense hose nozzle setting. It wasn’t the jet setting, but the blobs of water were still landing pretty hard on the bare soil. I told him that these heavy water drops landing that way can cause compaction. So he switched to the mist setting.
A main problem caused by soil compaction is oxygen exclusion. The first time I ever made brownies, I followed the recipe closely, carefully sifting the flour. Then for good measure, following the sifting, I tapped the stainless steel mixing bowl to settle the flour. My better half saw what I had done, then pointed out the error of my ways. The flour was supposed to stay fluffy. My future brownie efforts (with properly sifted flour) fared much better.
Similarly, soil should be fluffy. Heavy traffic on a field causes compaction. Plowing can cause a plowpan, a type of compaction. Disking a field when too wet often causes compaction. Any tillage operation should throw some dust, be it mold-board plowing, disking, chisel plowing, row-cultivating, or other secondary tillage methods. Dust presence indicates less likelihood of soil compaction. Conversely, heavy rains hitting bare soil cause compaction, which in turn lowers soil porosity and oxygen levels.
Less soil oxygen means lack of aeration. Such anaerobic soils discourage most desirable crops, inviting undesirable plants — commonly called weeds — to germinate. A couple years after the greenhouse compaction demonstration, the weed which drew most of my attention was horse nettle (Solanum carolinense). (Regular tomatoes, potatoes, and most peppers belong to genus Solanum.) One of my columns, that particular year, dealt with horse nettle in late August. A woman subscriber, in southeastern New York, questioned me about the weed, suspecting her own horse nettle infestation.
She boarded horses, in addition to a few of her own equines; most of the hay she harvested was bought by other local horse owners. The last thing she wanted in her horse hay was horse nettle! Her verbal weed description matched my printed description. Most of the specimens were about a foot tall, had light purple flowers, and sharp prickers, these in turn surrounded by short hairs. She said there were no berries yet. I told her that when the berries did form and ripen, they would be orangish-yellow (like miniature grapefruit) — and toxic!! I was quite certain — without physically examining these weeds — that the problem plant was horse nettle, a.k.a. wild tomato, a.k.a. Carolina nightshade (hence the species name carolinense).
She hadn’t recently soil-tested the fields in question — but planned too soon. I told her that most likely the phosphate levels were too low. Other factors encourage the development of S. carolinense, but the three most prominent ones are low oxygen, low phosphate, and low calcium base saturation percentage. Most cropland in her area has consistently low pH, and thus needs more lime. I told her that we should be as accurate as possible in determining the soil’s needs, and that, for starters, she should get a lime spreading service lined up.
2018 has been a year for Queen Anne’s Lace (wild carrot)… much more than horse nettle. Soil samples from a reactivated farm (that I submitted earlier this year to Dairy One Lab in Ithaca) showed interesting data. Results for the meadow with the worst wild carrot infestation showed pH 6.8 (not surprising for a Lima silt loam), very low phosphorus (8.5 ppm, Mehlich 3), sulfur very low at 5 ppm, organic matter at 6.8 percent (very nice), and magnesium base saturation very low at 7.1 percent. So we didn’t need any lime at that high pH. A couple hundred pounds per acre of Epsom salt (magnesium sulfate) would work wonders on those sulfur and magnesium issues. For the phosphorus, the soil test results said to apply 50 pounds per acre actual phosphate, these days most likely mono-ammonium phosphate (organic folks could use a mined rock phosphate and/or bone meal). Soon after these corrective soil amendments were applied to this Lima silt loam, alfalfa and clover seed, lying dormant in the seed bank, popped to life.
In his November 2018 On-line Newsletter (advancedagsystems.com.), Certified Crop Advisor Tom Kilcer wrote: “The wide spread soggy conditions that started in mid-July have continued through harvest across most of the New England, Mid Atlantic, and upper Midwest dairy regions. The corn silage was too dry to harvest and fields were too wet to drive… The end result is tremendous amount of soil compaction across all soil types. It happened, now how can we correct it?”
I’ll pick a couple of the answers Tom gave to his own question. He said frost will not remove compaction. What is lifted by the frost settles to the same density after thaw. A more effective system is a holistic approach with a mix of prescription tillage and fibrous deep-rooted crops. Tom says the latter is critical. If you loosen the soil and plant corn, there is nothing to stabilize it, and structure will collapse again worse than before.
Quoting Kilcer directly, “As soon as the ground is friable, simply work the top 6-7 inches with a chisel and plant. Resist the temptation to run the chisel as deep as it can go. First, the lower layers are wet and you will assure the lower layers laterally compact to the consistency of a paved interstate even if the top looks nice.”
Soils that are too wet to kick loose any dust — when subjected to any form of tillage — land much harder than dusty soils, due to heavier weight associated with all the contained water. Such water-logged Northeast soils were the rule — not the exception— in growing season 2018.