Shalom Benny!
We have not tried the green manure. It would be much too costly to sow seed to do that, plus the wear and tear on our machinery plus fuel. The closest we get to that is summer fallowing a field. That means we work the weeds down to kill them. We're finding some of the weeds are requiring this since it's been so wet.
1.+2. We do grow legumes...it never occurred to me to mention it...lol. I believe we have two fields in soybeans this year. VERY expensive input costs...but hopefully the crop will bring good returns. We've only grown soybeans once. I really like them. They're nice to work with. Peas are a pain in the backside. They make very good tasting lamb meat but every time we grow them, they lodge (lay down flat on the ground, usually caused by high winds) and are almost impossible to pick up. We stopped growing them for this reason. We haven't found a variety that meets our expectations.
Our fields are in constant rotation and we also change variety of the crop...one has to do that to keep from getting plant diseases occurring. We also have hay crops sown, consisting of alfalfa/brome and separate fields of green feed. The hay fields are rotated every so many years. We only get one hay crop the majority of the time...it's expensive to establish hay so it's left down for a few years before it's put back into crop production.
3. We do leave the plants and they are worked back into the ground. That's what the chopper on the combine does. It's like a large mulching lawn mower. If I drop the straw that means my husband round bales the straw behind the combine for bedding for the cattle. The straw wouldn't get worked back in. I assume we'll be baling the oat straw for bedding for the cattle. The guys will be swathing that whole quarter down tomorrow with two swathers while the the boy and I combine the wheat.
4+5. Both fertilizer and chemical cost as does fuel and equipment wear; farmers here don't put anymore on than they have to and we make as few passes as possible. These input costs easily reach six figures.
