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 (...)
Synergistic Effect of High Temperature and High pH on the Destruction of Salmonella enteritidis and Escherichia co1i O157:H7.
This study was undertaken to determine if high temperature and high pH interact synergistically to enhance the rate of destruction of two important gram-negative foodborne pathogens, Escherichia coli O157:H7 and Salmonella enteritidis . The rates of destruction in NaHCO3-NaOH buffers at pH 7.0, 10.0, and 11.0 were determined at 35, 40, 45, 50, 55, 60, and 65°C. Use of an improved heating protocol eliminated a "tailing effect" at longer exposure times. The present study demonstrated that the combination of high pH and high temperature resulted in a highly significant synergistic interaction (P > F = 0.0001), which caused rapid death of both E. coli O157:H7 and S. enteritidis . This "alka-therm" technology might be used commercially to destroy gram-negative foodborne pathogens on various raw agricultural commodities.