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
The Effect of Surface Cover on Soil Moisture Losses by Evaporation
RECENTLY, Duley and Russel proposed for experimental consideration a new method of farming that they call "sub-surface tillage" (3, 4). By this method soil would rarely if ever be turned upside down, but would be handled as regards all operations of seedbed preparation, planting, and tillage, in such manner as to leave all residues so far as possible on the surface of the ground. This method has four objectives: namely, facilitated infiltration, reduced evaporation, decreased erosion by water, and improved control of the hazards of blowing. In another paper Duley (i) has dealt with experimental work being conducted by the Soil Conservation Service and the Nebraska Experiment Station on factors affecting infiltration. This paper will deal with the question of surface evaporation.
Replant Management Strategies Influence Early Growth of Apple Trees in a Sand Soil

Two field experiments were conducted to evaluate the influence of rootstock (seedling, M.26, MM.106), soil fumigation (metam-sodium, methyl bromide), and planting hole substrate (original soil, non-orchard soil, organic mix) on early growth of ‘Granny Smith’ apple trees (Malus domestica Borkh.) in a Quincy sand. Application of soil fumigants in the fall before tree planting the next spring or replacement of the original soil with non-orchard planting hole substrates having greater water-holding capacity and nutrient status significantly improved tree growth. Combination of fumigation and soil replacement had a synergistic positive effect on tree growth. The size-controlling characteristics of the rootstocks were evident in the non-orchard soil and organic mix treatments, but not when the trees were planted in the original orchard soil. Chemical name used: sodium N-methyldithiocarbamate (metam-sodium).