I own a Tortella 005 120 (47" spader from Italy) so here is my 2 cents.
Pros:
Trash burial - go into a field of annual rye cover and you can just punch it down into the ground. If you go over that after with a shallow tiller you get a nice seed bed with good organic matter incorporation
Hardpan cracking - my Tortella spades 10" deep and does an awesome job of breaking the hardpan created by other implements and tilling. This does improve water flow through the soil.
Cons:
Expensive - New my Tortella would have been $7500. Thankfully I didn't have to pay for it.
Hard on Equipment - I know they say it is easier on the tractor then a tiller but that is total crap. I run mine on a 32hp Kubota and it shakes that poor little tractor to pieces. No matter how hard I tighten the sway chains, after 2 hours of spading the slacks are loose and the top link has gotten longer. My 48" Sovema tiller on the other hand is so smooth I can hardly notice it, unless I hit a rock or root. If the tortella hits something strong enough it will jump right out of the ground and slam back down.
The spader definetely has its place, especially if you do a lot of cover crop incorporation,and it is very well built, but it is a limited tool. I used to use it for almost all my tillage, but now use a cultivator and very shallow rototilling unless I need to incorporate a lot of organic matter. I kinda got carried away with it, but it looses it advantage if you use it too much.
I am all for building your own equipment, I do it all the time, but seeing how heavily built my Tortella is, I would worry about using engine components.
A few questions:
1. Do you have an idea on how wide of a track you want to cover?
2. How deep do you hope to go? Any less then about 7 or 8 inches and I would likely be using a disc. They are cheaper and far faster.
3. What is your primary use going to be?
I think spaders are great for their specific purpose, but I would have a few concerns building my own. The 47" sometimes works my 32hp tractor and weighs 800#. You need the weight to hold it down and although the 4100 could probably lift it, I think it would struggle to run it. Im not really trying to discourage you, just my own opinion from experience, but if you were just after breaking up the hardpan I would find a subsoiler your tractor can pull or hire it out once a year. A good cultivator can break up most hardpans created by rototilling and the subsoiling would do a good job cracking the hard ground below that without disturbing soil structure too much.
If you still want to build then I support 100% and if you need any dimensions or photos from mine just let me know.
