A METHOD TO SCREEN WEED-SUPPRESSING ALLELOCHEMICALS IN FLORIDA BIOMASS
Wood chip mulches derived from woody species grown in Florida are sometimes used for weed suppression in perennial fruit crops, especially in sustainable and organic production systems. A method for testing allelopathic qualities of these materials was developed, including wood chip incubation and filtering followed by bioassays of lettuce seed germination and growth. Eluates of wood chips from red maple ( Acer rubrum cv. ‘ Rubrum ’ L.), swamp chestnut oak ( Quercus michauxii Nutt.), red cedar [ Juniperus silicicola (Small) E. Murray] and sweet bay ( Magnolia grandiflora L.) highly inhibited germinating lettuce seeds, as assessed by germination percentage, radicle and hypocotyl growth. The effects of eluates from these four species were more than or equal to that found for eluates from wood chips of black walnut ( Juglans nigra L.) a species with a high level of allelopathic activity. In the United States annual estimated waste biomass of urban tree and wood mill residues totaled 38,000 and 5,600 dry metric tons, respectively (National Research Council, 2000). Wood chip mulches from such biomass applied as a preor post-plant treatment have been shown to suppress weeds (Autio, 1999), moderate soil temperature (Harris, 1983), soil moisture (Russel, 1939), and increase growth of young pecan trees (Foshee et al., 1996; Smith et al., 2000). Experiments to determine allelopathic activity of woody species and their derived materials have included interplanting corn with black walnut (Jose et al., 1995) and application of plant tissue extracts to weeds growing in the field (Al-Saadawi and Al-Rubeaa, 1985; Al-Saadawi et al., 1985). Other laboratory studies assessing allelopathic activity of cover crops have used germinating lettuce seeds as a test crop because of its high sensitivity to bioactive substances (Fujii and Shibuya, 1992). Our objective was to test a laboratory bioassay for allelopathic chemicals from wood chips of species commonly found in woody biomass waste management operations. Once developed, such a laboratory bioassay could be used to evaluate biomass allelopathic potential prior to longer term field trials. This research was supported by the Florida Agricultural Experiment Station and approved for publication as Journal Series No N-02514. This research was supported by a grant from the University of Florida Center for Biomass Programs. 1 Corresponding author
Improving the growth of newly planted apple trees
Increasing the N application rate (in the form NH 4 NO 3 ) to newly planted Marshall McIntosh'/M.9 apple (Malus domestica, Borkh.) trees beyond 76 g N per tree per year reduced growth in the first two growing seasons. Peat moss or composted manure mixed into the planting hole of Royal Gala'/M.26 increased growth in the first growing season after planting. The soil-active fungicides, fosetyl-Al and metalaxyl, increased trunk and shoot growth of Royal Gala'/M.26 in the first season after planting (...)
ALLELOPATHY AND ITS INFLUENCE ON THE DISTRIBUTION OF PLANTS IN AN ILLINOIS OLD-FIELD
SUMMARY (1) A whole-community investigation of allelopathy in an old-field in Illinois was undertaken, by comparing bioassay results with association patterns in the field. (2) The seven most abundant species in the field were tested upon each other in nine commonly-used bioassays. Eight of the nine bioassays gave many cases of statistically significant inhibition, and strong phytotoxicity was exhibited by species which have not previously been suspected of being allelopathic and which show no readily-observable signs of allelopathy in the field. (3) Autotoxicity was found to be as severe as allotoxicity, indicating that the species have not evolved resistance to their own inhibitors. (4) When the distribution patterns of species in the field were statistically compared with the results of each of the bioassays in turn, no significant correlations were found. (5) It was concluded that the types of allelopathy which were tested by these bioassays were not demonstrably effective under field conditions, that perhaps any species can be shown to have allelopathic properties in bioassays, and that bioassays may, for many communities, have no ecological meaning.