Market Farming

[Steve Diver <steved AT ipa.net>]

>How long does the rye residue inhibit the sprouting of small seeded 
>crops?  I could not get oats untreated this fall, so planted rye instead 
>but am concerned about the suppression factor for early crops. We have a 
>spader which can chop and incorporate pretty well if that is beneficial.
>
>Scott


Alan R. Putman, a horticulturist at Michigan State University,
was one of the early pioneer in sustainable agriculture who 
brought attention to allelopathy from cover crop mulches as a 
non-chemical weed suppression tool.
 
The bottomline is that rye, barley, sorghum-sudan, buckwheat,
oats, and a few other cover crops can function as allelopathic
weed suppressive cover crops..... if you undercut or roll-down 
the cc biomass and leave it on the soil surface as a killed mulch.

The intact stems leak out allelochemicals which function as
natural pre-emerge herbicides.  The weed suppressive
effect is pretty good for about 30 days. After that, the 
effect wears off and you'll see little weed sprouts poking
thru the mulch.   The effect might last fairly well for
30 to 40+ days. 

There's many factors that effect how much weed suppression you 
get and how long it is effective:  biomass, mulch coverage,
weather, past history of field, cover crop species, etc. 

One of the outstanding benefits of the mechanical roller-crimper 
popularized by Rodale/NewFarm.org is this weed suppressive 
mulch effect, in part, due to allelopathy.   

Putnam and others found that allelopathy is most effective
against small-seeded weeds (pigweeds, lambsquarter,etc), but 
the double-edge sword in cropping systems is that it can also 
be suppressive to small-seeded and medium-seeded veggie crops 
(lettuce, carrots, cukes, etc) that follow these cover crops.

SINCE you are employing the spading machine, this changes
the dynamics of the cereal rye. CC biomass that is incorporated 
is rapidly attacked by soil biology so you lose the allelopathic 
effect to a large degree.  The old recommendation, still used
widely, is to wait two weeks after cover crop incorporation
to avoid allelochemicals, nitrogen tie-up, and the like. 

The flip side is that you have very active soil biology
from cover cropping, composting, microbial teas, and spading...
then the waiting period can be reduced dramatically. 

Steve Diver
Texas