That looks very much like many clay soils I see often, very low in organic matter. What you want to get the level of OM to is between 6 and 8 percent which can be a fairly large amount of organic matter. Hugelkultur is a way of getting OM into the soil but can take a very long time. Compost, shredded leaves, and cover crops are quicker methods of amending soil.
Perhaps these simple soil tests might be of some help.
1) Soil test for organic matter. From that soil sample put enough of the rest to make a 4 inch level in a clear 1 quart jar, with a tight fitting lid. Fill that jar with water and replace the lid, tightly. Shake the jar vigorously and then let it stand for 24 hours. Your soil will settle out according to soil particle size and weight. For example, a good loam will have about 1-3/4 inch (about 45%) of sand on the bottom. about 1 inch (about 25%) of silt next, about 1 inch (25%) of clay above that, and about 1/4 inch (about 5%) of organic matter on the top.

2) Drainage. Dig a hole 1 foot square and 1 foot deep and fill that with water. After that water drains away refill the hole with more water and time how long it takes that to drain away. Anything less than 2 hours and your soil drainsâ too quickly and needs more organic matter to slow that drainage down. Anything over 6 hours and the soil drains too slowly and needs lots of organic matter to speed it up.

3) Tilth. Take a handful of your slightly damp soil and squeeze it tightly. When the pressure is released the soil should hold together in that clump, but when poked with a finger that clump should fall apart.

4) Smell. What does your soil smell like? A pleasant, rich earthy odor? Putrid, offensive, repugnant odor? The more organic matter in your soil the more active the soil bacteria will be and the nicer your soil will smell.

5) Life. How many earthworms per shovel full were there? 5 or more indicates a pretty healthy soil. Fewer than 5, according to the Natural Resources Conservation Service, indicates a soil that is not healthy.

Whether there is enough N to make significant heat depends on how much fertilizer and grass clippings and manure is in your layers. But that may be a moot point: if you cover it with soil the oxygen input will probably be slowed to a point where it will not heat up.

I think you could do this any time, the sooner the better. I myself would use minimal to no fertilizer and let the organic materials provide the nutrients.

If you are planting right over it and the N is too high, it can certainly damage the plants whether the temp is hot or not. You might want to plant to the side a little and let the roots find it?

Thank you for the replies.

I'd avoid tilling the whole area since the SFW is quite damaged already, not to mention it would be very labor intensive due to the soil structure. Hence the planting to the side might prove difficult for the plant in terms of roots penetrating through the hard clay.

I'll post the results mid and late season for future reference.

Cheers,
Djole

I would still trench and bury as much manure as I can. For that type of soil top dressing does not work.

Hugelculture was developed as a way to get plants up and out of clay soil. The pit you dig would probably go anaerobic on you because it's in clay and that would not be good for your plants. Chipping up the branches, or using then as sides for a raised bed, would be a better use of them.

It's better to amend a small area well than to thinly cover a larger area because you ran short of material.

Layer large quantities of whatever organic material you can get - several layers of newspaper, then stable straw, dead leaves, tree chippings and a bit of high nitrogen chicken or turkey waste ... right on top of the clay soil. Don't till.

Pile it 6-12 inches thick ... then go on to the next section when you get more material.

When you get to planting time, plant right in the organic material. The tomato roots will go through the newspapers into the clay looking for water.

Leave the forest alone - the trees are stressed because of the drought and need as much of thgeir own organic material as they can get.

Hi Djole: I like your soil layering method. My soil is heavy clay, rock-hard dolomitic with limestone, pH 7.7. Most likely your soil pH is alkaline, high in magesium like mine.

I had the best bumper crop of tomatoe when I used fresh cow manure pH 4 ... but they don't sell that stuff anymore, the cow manure in bags is very alkaline now, pH 8, due to the lime added to deodorize.

The second best bumper crop was when I raked FRESH grass clippings lighly onto the top 6" of soil. U. of Connecticut documented the release of nitrogen from grass clippings is 1 month. NPK of grass clipping is 4-0.5-2, quite high in nitrogen.

Tomato Tone NPK is 3-4-6 for neutral/acidic soil. If your soil pH is alkaline, phosphorus will be tied-up, so you would need a much higher number of phosphorus fertilizer. I didn't give my tomatoe last year high phosphorus, with the grass clippings it became too tall, too green, and not much fruits.

The best method to fix heavy and alkaline clay? Check out the link below. Trust me, I experimented with 10+ different holes for my roses, the below method is the best for deep root. The method below is for acid-loving plants, but it makes the soil so fluffy that tomatoes love it.

"In clay soils, a mixture of 50 percent ground pine bark, or leaf mold from pine or oak leaves, 25 percent coarse sand and 25 percent topsoil could be used. Avoid using a large amount of peat , especially for rhododendrons, because peat-amended soil may hold excessive moisture during wet conditions in winter and spring." .....

Peat doesn't work well with clay, since it binds up and become cement when dry. Pine bark, leaves, and coarse sand is best. Pine bark is acidic at pH 4 to 5, with 21% moisture retention when decomposed.

Here is a link that might be useful: University of Missouri on fixing heavy clay