- till back into the soil to add organic matter
- make compost of the tops, and till the roots back in (especially legumes)
- prevent erosion
But now I grow them for a different reason. Phytoremediation. (Cleaning the soil with plants)
Around here, all compost piles have become bio-accumulators of cesium.
Everyone knows that your compost pile shrinks up to 60%. Well it came to me over the winter, that means that the compost I made has 3x as much radiation contamination as the original leaves and stems did! And I harvest weeds and grasses to compost from all over the acre or so that I mow. If I spread this back on my garden, it would greatly increase the concentration in the garden beds! Thank goodness I realized that over the winter, and not after I spread it! The goat's manure is also a no-no, since they only eat local grasses. But the cow manure I bought should be relatively clean, since cows here eat mostly imported hay and feed from the US. No grazing for the poor things.
So now I am reverse green manuring. I take the plants and roots out, and trench compost them in a clay lined trench in the corner of my property, and don't return the compost.
This strip mining will probably wreak havoc on my soil. Only time will tell.
By trench composting, I can cover it with thirty centimeters of soil- which will cut 90% of the gamma rays. And cesium binds to the clay lining, which should keep it from penetrating further.
But it looks like I will have to use imported organic fertilizer, or chemical fertilizer for at least a few years. Sigh. I draw the line at pesticides/herbicides/fungicides though.