Allelopathic potential of leachates derived from landscape mulches on weed seed germination

Greenhouse and laboratory experiments using leachates at various strengths from several decomposable landscape mulches and other types of decomposable materials were conducted to determine the influence on several weed seed species.

Leachates for the experiments were collected either by mist percolating through the mulch for one hour or by soaking the mulch for six hours or 24 hours. Four groups of experiments were conducted.

Group I consisted of eleven experiments conducted in the greenhouse over a period of eleven weeks. Leachates from a single mulch were collected from three different mulch layers and used to germinate four weed seed species. A bioassay using duckweed to test the variables associated with differing amounts collected and the variation of color in the leachates was a second series of experiments under Group I.

The leachates in the Group II greenhouse experiments were collected by soaking the mulches for six or 24 hours, collecting the leachates and germinating weed seed species placed in sand.

The experiments in Group III and Group IV were conducted in a laboratory under more controlled conditions. In both groups of experiments, seeds were germinated in petri dishes on filter paper. The leachates for the experiments in Group III were collected from mulches that had soaked for six and 24 hours. The resulting leachates were used full strength, half strength and one-third strength.

Leachates in Group IV experiments were collected by soaking the mulch for 24 hours; reapplying distilled water, soaking for another 24 hours; and reapplying distilled water for another 24 hour soaking period. These leachates were used to test this dilution method on weed seed germination to determine if repeated exposures to water effected the mulches ability to inhibit or stimulate seed germination.

Overall results indicated that no one mulch leachate effectively stimulated or inhibited the germination of all the seeds tested. However, the various methods of testing indicated that cocoa bean hulls, red maple and cedar leachates inhibited a wider variety of seed species than the other mulches. Leachates from barley stimulated the germination of annual rye.