The phenomenon you are asking about is allelopathy.
Remarkably, it has its own journal - Allelopathy Journal (ISSN:
0971-4693) published since 2009 and currently at volume 30, issue 1.
Here are the titles of the papers from the most recent issue:
In-vitro assessment of allelopathic effects of wheat on potato.
Allelopathic effects of sunflower on seed germination and seedling growth of Trianthema portulacastrum.
Effects of simulated acid rain on the allelopathic potential of invasive weed Wedelia trilobata.
Allelopathic effects of Brachiaria ruziziensis and aconitic acid on Ipomoea triloba weed.
Effects of Butia capitata pyrenes extracts on the germination of lettuce seeds.
Effects of root exudates from crop plants on the growth of Fusarium oxysporum f.sp. niveum.
So, if you have specific questions, this might be the place to look.