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C. Stevens, V. A. Khan, A. Y. Tang, and R. M. Cody

Field plots on Norfolk sandy loam soil at Tuskegee and Eufaula, AL were treated by soil solarization (SS). Samples rhizsosphere (R) and nonrhizosphere soil from cole crop and strawberry plots were collected and assayed with selective media for population densities of microbes involved in organic decomposition and mineralization. Microflora population densities of bacteria, actinomycetes and fungi increased 2-7 folds in the solarized compared to the bare soil (BS). Microflora population densities in the soils involved in cellulose and protein decomposition, ammonification, nitrification, phosphate mineralization were greater in solarized soil compared to BS. Nitrogen-fixing bacteria in R soil 7 months after SS was higher when compared to BS at Tuskegee, but was reduced 50 folds 18 months after SS.

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I.A. Merwin and W. C. Stiles

Eight groundcover management systems (GMS) have been evaluated since 1986 in an apple orchard replant site. Tree-row GMS have included post-emergence herbicide (glyphosate) “killed sods,” pre-emergence herbicide (norflurazon + diuron) strips, a crownvetch “living mulch,” hay-straw mulch, monthly cultivation, a close-mowed sod, and an unmowed, chemically growth-regulated (maleic hydrazide + 2,4-D) sodgrass. Soil organ&matter content, surface aggregate structure, and water infiltration have improved under vegetative groundcovers relative to herbicide treatments. Extractable soil N, K, P and B have increased under straw mulch. Except for K, foliar nutrient content (dry wt basis) has not been closely coupled with soil nutrient content. Leaf K, P and B contents have increased, while leaf N, Mg and Zn, have decreased in trees in sodgrass relative to herbicide GMS.

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James H. Cane and Daniel Schiffhauer

Cranberry flowers (Vaccinium macrocarpon Ait.) require bee visitation for pollination. Bees visit cranberry flowers for nectar and sometimes pollen, but honey bees (Apis mellifera L.) in particular often work alternative co-flowering species for nectar, presumably because cranberry offers inferior nectar rewards. In a common garden setting, replicated plots of the cultivar Stevens were found to secrete significantly more nectar sugar (25% to 35% more) per flower than either `Ben Lear' or `Early Black', two other common commercial cultivars. The nectar secretion rate of `Stevens' was unaffected by a 4-fold range of fertilizer application rates over the preceding 2 years. These results are compared to studies of other crops involving varietal differences and programs of selective breeding for nectar secretion.

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Alan Kahler and Charles Sherwood

Abstract

Thirty-five pairs of shade trees were studied to determine the relation of premature senescence and resulting early defoliation to annual growth and conditions in the upper soil about the tree. The late defoliating trees experienced more radial and linear growth over the preceding five-year period. Regression analysis of radial on linear growth within each tree group revealed near linear to linear relationships for the late defoliating trees but nonlinear relationships for the early defoliating trees. Early defoliators had higher levels of N, P, and Ca in the soil about the tree at three soil depths tested. Significant positive correlations occurred between the levels of soluble salts, N, and P; between Ca, P, and N; and between K and radial growth in the early defoliators. Significant negative correlations occurred between levels of Ca and radial and linear growth. For the late defoliators, significant positive relationships were found for levels of soluble salts, N, and Ca and between radial and linear growth, with significant negative relationships between levels of P and Ca, and between N and linear growth.

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R. W. Roncadori and F. A. Pokorny

Abstract

Total fresh weight and crown spread of Juniperus chinensis var. sargentii Henry plants, grown in microplots containing a low fertility medium of 4 soil:l sand:l milled pine bark and amended with 10N-4.4P-8.3K fertilizer at rates of 0, 110, or 220 μg/g, were significantly increased by inoculation with a spore mixture of 3 different vesicular-arbuscular (VA) mycorrhizal fungi. Higher fertilizer concentrations improved crown spread but did not affect plant growth. Root colonization by the endophytes ranged from 24.4 to 39.2% and was unaffected by fertilization rates.

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Laura K. Paine and Helen Harrison

Since the domestication of the first crop species, farmers have dealt with the problem of soil depletion and declining crop yields. Fallowing of land was the first approach to restoring soil fertility, and is still the most commonly used method among indigenous farmers. Alternatives to fallow, such as crop rotation and green manures, developed in a number of areas. The earliest record of their use is in Chinese writings from ca. 500 B.C. Discussion of these practices is found in European agricultural publications dating from the 16th century. While these ancient techniques have proven value for soil conservation, their use in modern agriculture is quite limited. Renewed interest within the agriculture community in recent decades has resulted in a greater research effort in the areas of green manures, cover crops, and living-mulch cropping systems.

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R.S. Mylavarapu

High-quality diagnostic soil, plant, and water-testing programs are required to achieve optimum agricultural production and to minimize negative environmental impacts. While soil fertility assessments and field-calibrated nutrient recommendations

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Timothy K. Hartz, P. R. Johnstone, E. Williams, and R.F. Smith

leaf P and leaf Mg at the preharvest stage ( r = −0.26), yet mean preharvest leaf Mg was the same for both yield groups (3.4 g·kg −1 ). This field survey approach did provide an opportunity to evaluate the soil fertility management practices of the

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Ashley A. Thompson and Gregory M. Peck

to improving soil fertility and reducing N loss is to use carbon-based amendments, such as composts. In apple orchards, compost applications have been shown to improved edaphic properties, including soil OM, microbial biomass carbon (C), microbial

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Monica Ozores-Hampton, Philip A. Stansly, Robert McSorley, and Thomas A. Obreza

Many vegetable growers rely on methyl bromide or other soil fumigants to manage soil pathogens, nematodes, and weeds. Nonchemical alternatives such as solarization and organic amendments are as yet largely unproven, but do offer promise of more sustainable solutions. The objective of this study was to evaluate the effects of long-term organic amendments and soil solarization on soil chemical and physical properties and on growth and yield of pepper (Capsicum annuum L.) and watermelon (Citrullus lanatus [Thunb.] Manst.). Main plots consisted of a yearly organic amendment or a nonamendment control. Four subplots of soil sanitation treatments consisted of solarization, methyl bromide, Telone, and nonfumigated. Each subplot was divided into two sub-subplots, one with weed control and one without weed control. Plant biomass was higher in plots with organic amendments than in nonamended plots. There were no differences in marketable pepper and watermelon yields between organic amended and nonamended plots during the 1998-99 and 1999-2000 seasons, respectively. However, higher pepper yields were produced from organic amended plots in the 1999-2000 season. Soil pH and Mehlich 1-extractable P, K, Ca, Mg, Zn, Mn, Fe, and Cu were higher in organic amended plots than in nonamended control plots. Soil organic matter concentration was 3-fold higher in amended soil than in nonamended soil. Effects of soil sanitation and weed management varied with crop and season. The methyl bromide and Telone treatments produced higher yields than soil solarization. In general, weed control did not affect plant biomass and yield for any of the crops and seasons. The results suggest that annual organic amendment applications to sandy soils can increase plant growth and produce higher or comparable yields with less inorganic nutrient input than standard fertilization programs.