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M.L. Arpaia, G.S. Bender, and G.W. Witney

A project evaluating the performance of cv. Hass on eight clonal avocado rootstocks—G755A, G755B, G755C, Duke 7 (D7), Borchard (BR), D9, Toro Canyon, and Topa Topa was established in southern California in 1986. Two additional rootstocks, Thomas and G1033, were added in 1987. Of the trees planted in 1986, the BR and D7 rootstocks have consistently had the highest total yields for all rootstocks, whereas the three G755 selections have had the lowest productivity. No differences in productivity between the two rootstocks planted in 1987 have been detected. The influence of rootstock on the magnitude of alternate bearing will be discussed, although the oscillation in yield is greater for the higher-yielding rootstocks. Tree size has been measured throughout the study. The BR selection has consistently produced a larger tree, even though it has continued to have high productivity. There are no consistent differences between the other rootstocks. Yield efficiency, measured as the kg fruit/m3 of canopy volume has been calculated. In selections that are prone to severe alternate bearing, the swing in yield efficiency is also the greatest. The data thus far suggests that a yield efficiency of ≈2.5 kg fruit/m3 canopy volume is the maximum yield possible for California `Hass' avocado.

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Nicole E. Burkhard, Derek H. Lynch, and David C. Percival

Within-row weed management of highbush blueberry (Vaccinium corymbosum L.) is reliant upon herbicide applications. However, in organic production, herbicides are typically not permitted and alternative methods must be used. The impact of thick (25-cm) mulch applications on weed pressure in an organic production system was initiated at a commercial operation in Nova Scotia, Canada, during 2005. A split-plot experimental design was used with five blocks (replications), six treatments, and five plants per split plot (cv. Duke). The whole-plot factor consisted of mulch/fertility treatments and included: i) control (no amendment); ii) ammonium sulphate fertilizer (30 kg·ha-1 N); iii) pelletized poultry manure (60 kg·ha-1 N); iv) pine needles (80 t·ha-1); v) horse manure and sawdust compost (550 t·ha-1); and vi) seafood waste compost (360 t·ha-1). The split-plot factor consisted of level of hand weeding (–/+). Weed control was assessed by sampling percent ground cover and weed shoot biomass in three 0.25-m2 quadrats in nonweeded subplots. Blueberry leaf N content, plant canopy volume, and berry yield (fresh weight and number) were recorded. The manure/sawdust compost and pine needle treatments had the lowest weed biomass and percent ground cover values, thereby providing the best weed control. Weed shoot biomass, blueberry leaf N, plant canopy volume, and berry yield were greatest in the seafood waste compost treatment. Results from this preliminary study indicate the potential of using these groundcover treatments to improve organic cultural management practices.

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M. Ozores-Hampton, H.H. Bryan, B. Schaffer, and E.A. Hanlon

The effects of municipal solid waste (MSW) materials on growth, yield, and mineral element concentrations in tomato (Lycopersicon esculentum Mill.) (1991 and 1992) and squash (Cucurbita maxima Duch. Ex Lam.) (1992 and 1993) were evaluated. Agrisoil compost (composted trash), Eweson compost (co-composted trash and sewage sludge), or Daorganite sludge (chemically and heat-treated sewage sludge) were incorporated into calcareous limestone soil of southern Florida. The control had no MSW material added to the soil. The effect of MSW on crop growth, yield, and mineral element concentrations varied considerably between years for tomato and squash. In 1991, tomato plants grown in soil amended with Eweson or Daorganite had a greater canopy volume than plants in the control treatment. Tomato plants grown in Daorganite had greater total fruit weight (1991) than plants in Agrisoil and more marketable fruit (1992) than control plants. In both years, tomato plants in Agrisoil had higher root Zn concentrations than plants in the other treatments. In 1992, tomato plants in Eweson had lower root Mn concentrations than plants in the other treatments, whereas Mg concentrations in the roots were higher in the Daorganite treatment than in Eweson. Tomato plants in Agrisoil had higher Pb concentrations in the roots than plants in all other treatments. In 1991, leaves of tomato plants in Agrisoil had lower Ca concentrations than leaves of plants in the control treatment. In 1992, leaf Zn concentrations were greater for tomato and squash in Agrisoil than in the control or Daorganite. In 1992, canopy volume and yield of squash were greater for plants in Daorganite than for plants in the control and other MSW treatments. Although canopy volume and total squash fruit weight did not differ among treatments in 1993, plant height was greater for squash plants in the MSW treatments than for those in the control. In 1993, leaf Mg concentrations were greater for squash grown in Daorganite than for plants in the control or Agrisoil. In 1993, fruit Cd concentration was higher for plants with Eweson than for plants in the control or Agrisoil. However, the fruit Cd concentration in squash grown in Eweson compost (1.0 mg/kg dry weight) was far below a hazardous level for human consumption. Our results indicate that amending calcareous soils with MSW materials can increase growth and yield of tomato and squash with negligible increases in heavy metal concentrations in fruit.

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Neusa M.C. Stenzel, Carmen S.V.J. Neves, José C. Gomes, and Cristiane C. Medina

This study reports the performance (yield, tree size, and fruit quality) of 'Ponkan' mandarin (Citrus reticulata Blanco) on seven rootstocks, evaluated for 11 years under Southern Brazil conditions. Trees on C13 citrange had higher cumulative yield for seven harvests than those on trifoliate orange. Cleopatra mandarin, rough lemon, Rangpur lime, Sunki mandarin, and Volkamer lemon rootstocks maintained their values at an intermediate position and did not present any significant difference regarding C13 citrange, and trifoliate orange. Trees on C13 citrange and on trifoliate orange exhibited the lowest alternate bearing index. Cleopatra mandarin induced the greatest canopy volume, but it was not significantly different from Sunki mandarin and rough lemon. The smallest trees were those on Volkamer lemon and trifoliate orange. The highest yield efficiency came from trees on C13 citrange and the smallest on Cleopatra mandarin. Rootstocks did not significantly affect fruit weight.

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Ramzy Khoury and Jimmy L. Tipton

Evergreen elm (Ulmus parvifolia), southern live oak (Quercus virginiana), and South American mesquite (Prosopis alba) were irrigated at 75%, 50%, and 33% of reference evapotranspiration for 2 years in Phoenix, Ariz. Each tree was irrigated with twenty-nine 3.8-L·h–1 drip emitters to a depth of 90 cm. Initial trunk diameters were about 4 cm. Water use was monitored by heat balance sap flow gauges and related to canopy volume, projected canopy area, and total leaf area. Oak used more water than elm, and elm more than mesquite under all irrigation regimes. Irrigation regimes had a greater effect on oak and elm water use than on mesquite, but all trees maintained an acceptable canopy regardless of treatment.

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Thomas E. Marler and Frederick S. Davies

Growth responses of young `Hamlin' orange [Citrus sinensis (L.) Osbeck] on sour orange (C. aurantium L.) trees to microsprinkler irrigation were studied under field conditions from 1985 to 1987 to determine the most-efficient irrigation rates and duration. Trees were irrigated when available soil water depletion (SWD) reached 20% (high frequency), 45% (moderate frequency), and 65% (low frequency). Trees at the moderate and low levels received 49% and 13%, respectively, as much irrigation water as the high treatment. Canopy volume, trunk cross-sectional area, dry weight, shoot length, leaf area, total root dry weight and volume, and new root dry weight were similar for the high and moderate levels in 2 of 3 years, but were significantly reduced at the low level. Summer and fall growth flushes were delayed or did not occur at the moderate and low levels. More than 90% of root dry weight was within 80 cm of the trunk at the end of the first growing season.

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Ramzy Khoury and Jimmy Tipton

Evergreen elm (Ulmus parvifolia), southern live oak (Quercus virginiana), and South American mesquite (Prosopis alba) were irrigated at 75%, 50%, and 33% of reference evapotranspiration for 2 years in Phoenix, Arizona. Each tree was irrigated with twenty-nine 3.8-L·h–1 drip emitters to a depth of 90 cm. Initial trunk diameters were about 4 cm. Water use was monitored by heat balance sap flow gauges and related to canopy volume, projected canopy area, and total leaf area. Oak used more water than elm, and elm more than mesquite under all irrigation regimes. Irrigation regimes had a greater effect on oak and elm water use than on mesquite, but all trees maintained an acceptable canopy regardless of treatment.

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Thomas E. Marler and Grace B. Paloma

Container-grown Annona muricata seedlings were bare-rooted and re-potted in sand. Containers were irrigated daily with a complete nutrient solution adjusted to a pH of 3, 4, 5, 6, 7, or 8, and the seedlings were grown for ≈5 months. Numerous growth variables were measured, including canopy volume, increase in mass, and trunk diameter. There were no differences in growth measurements among the pH levels. Moreover, leaf tissue was analyzed for mineral content. Leaf tissue concentration of various minerals did not differ among the pH levels. Annona muricata is known for growing well in a range of soil conditions. These data verify that the species is adapted to a wide range of substrate pH.

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D.A. Devitt, R.L. Morris, and D.S. Neuman

A 2-year study was conducted to quantify the actual evapotranspiration (ETa) of three woody ornamental trees placed under three different leaching fractions (LFs). Argentine mesquite (Prosopis alba Grisebach), desert willow [Chilopsis linearis (Cav.) Sweet var. linearis], and southern live oak (Quercus virginiana Mill.) (nursery seedling selection) were planted as 3.8-, 18.9-, or 56.8-liter container nursery stock outdoors in 190-liter plastic lysimeters in which weekly hydrologic balances were maintained. Weekly storage changes were measured with a portable hoist-load cell apparatus. Irrigations were applied to maintain LFs of +0.25, 0.00, or -0.25 (theoretical) based on the equation irrigation (I) = ETa/(1 - LF). Tree height, trunk diameter, canopy volume, leaf area index, total leaf area (oak only) and dry weight were monitored during the experiment or measured at final harvest. Average yearly ETa was significantly influenced by planting size (oak and willow, P ≤ 0.001) and leaching fraction imposed (P ≤ 0.001). Multiple regressions accounting for the variability in average yearly ETa were comprised of different growth and water management variables depending on the species. LF, trunk diameter, and canopy volume accounted for 92% (P ≤ 0.001) of the variability in the average yearly ETa of oak. Monthly ETa data were also evaluated, with multiple regressions based on data from nonwater-deficit trees, such that LF could be ignored. In the case of desert willow, monthly potential ET and trunk diameter accounted for 88% (P ≤ 0.001) of the variability in the monthly ETa. Results suggest that irrigators could apply water to arid urban landscapes more efficiently if irrigations were scheduled based on such information.

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Thomas A. Obreza and Robert E. Rouse

The growth response of young `Hamlin' orange (Citrus sinensis L. Osbeck) on Carrizo citrange (C. sinensis × Poncirus trifoliatu L. Raf.) trees to N-P-K fertilizer rates under field conditions in southwestern Florida was studied to determine the minimum fertilizer required to bring trees into maximum early production. The highest 8N-1.8P-6.6K fertilizer rate was 2.72,5.45, and 8.17 kg/tree in 1989,1990, and 1991, respectively. Additional fertilizer treatments equaled 50%, 25%, or 13% of the maximum rate. Fertilizer sources contained either all water-soluble N (applied more frequently) or 40% to 50% controlled-release N (applied less frequently), and they did not affect fruit yield or quality. The response of trunk cross-sectional area, tree canopy volume, and fruit yield to fertilizer rate was described by a linear plateau model. The model predicted a fruit yield of 22.6 kg/tree at the estimated critical fertilizer rate of 48% of maximum. Fruit yield at the 50% maximum rate averaged 21.2 kg/tree. As fertilizer rate increased, total soluble solids concentration (TSS) in juice and the TSS: acid ratio decreased, but weight per fruit and TSS per tree increased. A fruit yield >21 kg/31-month-old tree indicated vigorous growth.