1) were efforts made to make sure the soil temperature was uniform across all treatments?  I will guarentee you that the soil temp will be cooler where the cover reside was laying, compared to bare open soil

2) Also, weeds light to have open, sun-lit areas to grow in.  I have often noticed that winter annual and perennial weed (i.e. dandelion) pressure is much greater where corn silage is harvested, compared to where corn is allowed to stand and harvested as grain.  Am I to presume that corn stalks also have allelopathic effects on weeds?  Or is this really an issue of weeds not germinating because they don't have sunlight?  I tend to think the latter is more true.

In years past, I have heard of this allelopathic effect.  But, I have also seen crop response to having that cover on the soil, especially in a relatively dry summer, where open bare soil will dry out.  I have also seen positive corn yield response in fields following wheat.

I am not going to say that allelopathy does not exist.  However, I don't think it is as important as some people would like to believe.  I think there are other, more important, effects going on.  And I have not seen enough allelopathic effects that I can comfortable reduce my herbicide use in the process.  Maybe others can...... but I haven't seen it yet.