A couple points re this and the original question:
Doug Kalmer wrote:Researching keyline plowing, I found this-
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http://onpasture.com/2013/06/17/keyline-plowing-what-is-it-does-it-work/
One needs to read the Part 2 post in this series, all the way to the end, to get to the most relevant information - the part where "that depends" is acknowledged, for example "Is it that keyline plowing is more suited for drier climates, where water is a limiting factor in production?"
Well duh. That's where it was developed and actually seems to make a difference, over decades at least. So assuming it will work the same in the completely different context of northern New England
dairy farms is problematic.
It's far too common that we transplant a context specific or context sensitive method, approach, system, to a significantly different context and assume it will work the same.
And this author is trashing keyline for 99% of the article, until admitting at the very end that maybe the context has something to do with it.
The "research" has its own problems, mainly in that the sample size is far too small for any statistical value, and the uncontrolled variables are far too numerous. Also the cherry-picking of outrageous claims of rapid soil-building as what one
should expect as a result. At least half the problem there is people making those claims.
However, anecdotally, it seems likely that keyline implementation is a waste of money in the context studied.
An open question is, does Holistic Management and similar short rotation grazing have benefits in that context?
And, did the fact that something like HM was already in use mean that adding keyline was moot because HM was already giving as much benefit as could be gotten?
If you read the details on how the animals were managed:
"Before and throughout the process, the dairy farmers maintained their grazing management. For three of the four farmers, herds of dairy cows or heifers grazed for 12 to 24 hours on the pasture, and farmers were careful to avoid overgrazing. ... The herds were brought into the paddocks when forages were at about 8-12” and came off before the forage reached 3-4”.
So these farmers were already doing something like HM grazing. If it was giving them benefit (more soil carbon, more root mass, etc. etc.), that benefit was already in place.
It could simply be that keyline couldn't add anything to the benefits already gained by HM, if any.
A better test of keyline would have been to implement it on land where HM type practices were NOT already in place.
Truly degraded, compacted, badly over-grazed land. Then we could see if there was benefit from keyline alone.
To the original question - the context you have, as described so far, is much more like where keyline was developed, than the northern New England dairy farm context.
And I assume you're not doing HM type grazing already?
So there's some chance you'll get more benefit from a keyline subsoil plow, used appropriately. It's always an experiment. Start small and see what happens.
The rest is pretty well covered by previous comments about what a swale is (vs. a diversion ditch), terrain impacts of swales vs. subsoil ripping, use of tree belts in classic keyline, etc.
Another question is, what is your soil composition? % clay? % sand? % of organic matter? And so on...a critical part of context when talking about any spread slow sink methods (swales, subsoil ripping, ponds, diversion ditches, etc.).
There are soils in which swales are a type one error, because when dug and wetted and exposed, the soil hardens to near or completely impermeable and nothing infiltrates (there's areas of stuff like that here in the Siskiyou region of southern Oregon). You get a long, narrow pond, with high surface area to volume and thus high evaporation losses.