I'm trying to kill off a large area (30'X30'X4') of living grass that has been established for hundreds of years. What would be the best way to kill off this grass? I do have a 30'X30' grain plastic tarp that I'm putting logs and pallets around/on the tarp and was wondering if I can do anything else to compress the area quicker to kill the grass in the area so I can hopefully do about a 700' long area during the winter winter in order to have wood chip trucks fill the area with free wood chips to try to establish a large garden next year with. I do know that this area will sink down a lot as it shakes a little when dropping about a 100 lbs log on the ground in area.
In general, I've heard technique of tarping over grass (and weeds and...) and killing it with heat and UV is called Solarizing while tarping to starve weeds of light is Occultation. If you use a clear tarp it's solarizing while opaque tarps are used for occultation. Another common method of covering soil is the "lasagne" method or the back to eden method, both of which are basically similar.
- Solarizing works by heating the ground using a clear plastic tarp for 4 to 6 weeks. It kills weed seeds in just the top few inches and also kills many small insects and fungi/bacteria. It also kills beneficial insects/fungi/bacteria, so you should balance that out after the solarizing process. If the soil is disturbed after solarizing, weed seeds from below the top few inches may be turned and may become viable. Here's an article on solarization
- Occultation is done similarly to solarizing: laying down an opaque tarp over the ground. This doesn't get as hot and tends to cause plants to germinate. Once germinated, they either die (if left in the dark long enough) or are in a weak state of growth that makes it easy for the gardener to simple pull them to kill them. Soil that has been treated by occultation should, again, not be worked as that will bring up viable seeds. Here's a good article on occultation.
- Lasagne gardening and Back To Eden gardening work as a form of bringing in a known-good soil on top of the old soil. This causes the same effect as the occultation process and the good soil on top should not have any weeds.
All of these processes should ideally result in the decomposition of that cut grass, but I'm not sure it is technically "composting."
I think the first step of all of these processes has to be to mat down or cut down the 4 foot tall grass. A string trimmer seems well suited to cutting it down, but it could take a while. If you "chop and drop" the grass then the cut stems can be combined with a carbon material to become the base layer in a lasagne garden. You could also try rolling over the surface with something like an ATV or tractor to simply flatten the grass stems before using one of the above techniques.
It sounds like you want to do the Back to Eden thing. I have no experience of this but
HOW TO GROW A BACK TO EDEN VEGETABLE GARDEN:
For an ideal Back to Eden garden, apply 3-4 sheets of newspaper. Then apply 3-4 inches of organic compost or composted manure. Then an additional 2-4 inches of wood chips or alternative covering on top. If you are implementing the methods in the Spring or Summer, additionally apply a dusting of composted manure for organic fertilizer.
WHEN TO COVER A BACK TO EDEN GARDEN:
For an ideal Back to Eden garden, cover your garden in the Fall! If you look at creation, nature drops its needles and leaves in the Fall. Note: *If you are using raw wood chips, allow time for them to break down (at least Fall - Winter). You will experience more work fertilizing with organic manure if you wait until the Spring or Summer to apply raw wood chips. Note: *If you are using composted wood chips that have had time to decay, you may apply and plant in the compost immediately. Note: *If you are using composted wood chips that have been screened, you may apply and plant in them immediately (Paul prefers this method for his home garden).
Composting is the decomposition using aerobic bacteriae usually of previously live biologic materials. So, you need to kill the grass first, and that's what the newspaper is for - to exclude light. You don't want to compress the area as that will cause soil compaction which doesn't help anything to grow. Plants need air spaces in the soil for their roots to breathe.
The old way of doing this would be to cut and stack the sod/turf on one side, till over the ground, let weeds appear, handle the perennial weeds that appear and then till again.
A sod cutter may be available for rent in your location; how long that would take would depend on how quickly you learn mechanical things and how carefully you can follow instructions. Otherwise 30x30 is not such a large area and might be cut by hand with a spade, which requires a strong back and determination. But since you appear to be tossing heavy logs with ease this will not be a problem. Turves are stacked upside down and allowed to rot like a regular compost pile, eventually to be returned to the new garden as a top dressing.