permaculture

[Toby Hemenway <hemenway@jeffnet.org>]

I agree that rye/vetch is an excellent cover crop; I used it 2 winters
running on a 4000 square-foot garden and definitely saw an improvement in
tilth and fertility. However, in comparison to sheet-mulching it had a
virtually insignificant effect. I inherited a garden with some real
problems: it had been "fertilized" with immense quantities of wood ash and
fresh manure, then watered with untreated, stored greywater (pH 9; storing
greywater is a no-no) so  the soil pH was 8.2 and the tilth was gone. It
had been red clay to begin with, thus it was very ugly. Gypsum plus cover
crops did a little good, but it wasn't til I scored 200 2-string bales of
spoiled alfalfa hay and a stable's-worth of wood-shaving manure, and
sheet-mulched a foot deep with it that I saw any real improvement. That
brought the soil life back in a big way, unlike the cover cropping.
Obviously you can't sheet-mulch on a farm scale, so there you must use
cover crops, but for any garden-scale work I've found that sheet-mulch is
infinitely more effective in restoring soil life, structure, and fertility
than cover crops. I did have very good results by seeding fava beans into
the fresh, fall-laid sheet-mulch; the big seeds had no trouble rooting in
the coarse mulch and the roots and nodules tied the mulch together with
fine-structure organic matter, plus the favas gave me a nice crop and more
mulch.
   I've seen some studies that show that cover crops are good for
preventing OM loss on cropland, but that the amount actually added each
year is 0.1 to 0.4%, so it's a slow way to build soil. Obviously it's
better than nothing, plus it protects soil, stabilizes nutrients, and
boosts soil life. I'm not knocking cover crops here-they're great-but scale
should point to the most appropriate technique, and for those working at
the right scale and with access to mulch materials, ya gotta go with deep,
and I mean deep, sheet mulch.

Toby