plow pan

hey john, my understanding is that the top 5 or 6″ of soil, or whatever you’ve ever plowed is disturbed soil and can be compacted by further use with a tractor or implement until you plow or harrow(or disturb it) again. your plow is a shovel and there is a flat pan where you stopped plowing that is soil from the dawn of time that no one has ever touched. it is harder than the gates of hell and can’t be compacted. it already has been by time. a chisel plow will reach down and scratch at that pan and give serious rainfall a place to go besides drowning out your crop. a spring harrow set real hard can bust it up a little. i guess once you have disturbed that layer, it is forever broken and can be compacted but not back to its original state. thats my belief on it.

mitch

@jac 21364 wrote:

Can someone explain to me please what mechanics are at play to create a plow pan ? I have assumed that this was a problem for tractor farms only… turns out horse farms have a pan.. and tractor farms have compaction as an additional problem. Does min till create a pan ? or is it only a plow that does this ?
John

A plow pan is a specific form of soil compaction caused by the action of a moldboard plow, typically over the course of time and usually after plowing at the same depth every year. Soil compaction is a loss of pore space in the soil. Pore space provides pathways for water infiltration and storage, oxygen movement and space for root penetration. Compaction is most often a problem caused by external forces, mostly from vehicles and animal traffic. Vehicles and animals compact the soil, mostly shallow and in the normal tillage zone, but it can go deeper with heavier vehicles, particularly if the soil is too wet for traffic or the soils have a distribution of coarse and fine soil particle sizes that cause the soil to set up tight. Grazing animals can cause severe shallow compaction and that becomes clear real quick to anyone pulling soil cores from pasture ground for a soil test.

Tillage is an external force that loosens the soil, but also, by the application of force, causes localized compaction. As a moldboard plow moves through the soil it pushes the soil apart. The soil at the cutting edge mostly is lifted, but some is pushed down and compressed under the point and share as the plow moves over it. This localized compaction can be aggravated by spring plowing because the soil is likely wetter at plow depth than near the surface. Plowing at the same depth each year contributes to a plow pan as will using worn points and shares with a blunt edge. A blunt edge pushes more soil before either lifting it or compressing it below the edge. These plow pans are often just an inch or two thick but can be quite dense and restrict water infiltration, drainage and root growth.

If by min-till you mean chisel plowing rather than moldboard plowing, generally, yes, it would be less likely to cause a plow pan because you are not compressing the soil uniformly across the bottom of the tillage layer, and you are moving less soil. But if you replace the moldboard with a disk, maybe not. The disk carries all its weight on the edge of the cutting disks and while it is good at loosening the soil above it tends to compact the soil below. So a disk could create a disk pan that would be much like a plow pan. As long as the soil is right for tillage one or two disking, just like plowing, is probably not going to be be a problem. But over time it can become a grey area in various shades of grey depending upon the level of compaction. So the solution is not in the name, it is in what you do.

Awhile back I read the book “Ten acres enough”. It is from the 1800’s about a fella that started a farm growing fruit. He told about making one pass with the walking plow followed by one pass with a subsoiler. He alternated all the way across the field.

John, it seems like it would work. The main thing is to open up the pan to let water and roots down in the ground. If a person had enough horse and not too much plow why couldn’t you make a device for the back of the plow.
It could be like a rolling basket on a field cultivator. Just make it to go directly behind the plow bottom. I don’t know if there would be enough room with more than one bottom, but it seems it would work with a sulky plow. Just a thought.

John, that would be interesting to try. It seems like it would take a fair amount of down pressure to break up a hard pan. So a trailing slitter would have to be quite heavy, and you fix it to your plow it might throw off the balance of the plow. Good luck with that.