Grow boxes - Making Soil

It's time to empty out some of my grow boxes and start them over again. Below is a picture of one box that I've opened and removed a couple buckets of soil out of it already. First of all, you can see that the surface of the soil has gone down a bit more than a foot from the top edge. Initially I overfilled the box by about 3 inches. So over the course of 6 months, the soil has settled quite a bit via decomposition of the organic material (grass clippings, weeds, compost, horse manure, and chicken litter).  I had expected that but I didn't know exactly how far it would go down. 

Next, I was impressed by the well developed root system the sweet potatoes made deep down into the box. The roots travelled all the way to the bottom although the tubers were in the upper 12 inches. 

I've opened this grow box and am taking some of the soil out to use in filling another grow box.
 You can see the deep root system that the plants made. 

When I loaded this box in the beginning, I placed the coarsest material on the bottom. The only pieces still intact were the bamboo chunks and 1 inch thick tree branches. Everything else had disintegrated or else was soft enough to crumble by hand as I unloaded the box.

Most of the organic material has decomposed, turning
into a medium brown soil. 

Most of the material I had originally put into this box is no longer identifiable. It is all crumbly and medium brown in color. As a bonus, I found a few dozen worms living in it. 

I emptied the box, returning to coarse stuff to the bottom. Then I refilled it with lasagna style, with thin alternating layers of  organic material (grass clippings, chicken pen litter, horse manure, weeds, waste mangos) and dirt which I took out of this box. I used 1/3 of the dirt for refilling the box. The rest of the dirt went to starting two new grow boxes.