Check out this peer-reviewed research paper on the subject: http://www.sciencedirect.com/science/article/pii/S0261219412000920
These researchers performed an experiment where they mixed up a variety of concentrations of ground Cannabis leaves to a soil mixture, planted plants, and then inoculated the soil with nematode eggs to determine if using Cannabis components as soil amendments will act as a nematode control.
After growing for a while the plants were harvested and the roots and plant shoots were measured to determine the magnitude of effect that the nematodes had on the plants as well as the number of nematode eggs present on the roots and in the soil. It was found that at a concentration of 10g of leaves per g of soil, the shoot length of the target plant increased by over 25% and the soil contained over 55% LESS nematode eggs compared to the control soil with no amendments.
More and more research is being conducted to find out if the antibacterial, antifungal, and insecticidal properties of Cannabis can be taken advantage of as a soil amendment.
Have some experience using Cannabis as a soil amendment? Share your experience!