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R.G. Linderman and E.A. Davis

Formation of arbuscular mycorrhizae (AM) has been inhibited in soilless potting mixes that usually contain some proportion of peat moss. The cause of the inhibition has been thought to be high fertilizer P content in the media that suppresses spread of the fungal symbiont in the root tissue. However, there has also been some suggestion that the peats themselves may contribute to the inhibition. That possibility was explored in this study. A sandy-loam soil, in which mycorrhizae consistently enhance plant growth under P-limiting conditions, was amended with six different peats. Onions (Allium cepa 'White Lisbon'), as an indicator host, were grown in the mixes under P-limiting conditions, and were inoculated or not with the AM fungi Glomus deserticola or Gigaspora rosea. Plant growth response to inoculation with AM fungi (AMF) varied with the type of peat and AMF isolate. Inoculated plants generally had the highest root biomass when grown in soil amended with peat. Root colonization by the two fungal symbionts was also affected differently by different peat amendments. Root colonization by Glomus deserticola and Gigaspora rosea was inhibited by at least half of the peat types. However, the types of peat inhibitory to Gigaspora rosea colonization were not the same as those inhibitory to Glomus deserticola colonization. These results indicate that different peat amendments can suppress or enhance mycorrhiza formation on onion roots and resultant growth benefit under P-limiting conditions, depending on the mycorrhizal fungus used.

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K.M Whitley and J.R Davenport

Potato (Solanum tuberosum) production in Washington State's Central Columbia Plateau faces nitrogen (N) management challenges due to the combination of coarse textured soils (sandy loam to loam) and hilly topography in this region as well as the high N requirement of potato. Potato growth and development can vary with the N availability across the field. In this 2-year study, two adjacent potato fields were selected each year (1999 and 2000). Each field was soil sampled on a 200 × 200 ft (61.0 m) grid to establish existing soil N content. One field was preplant fertilized with variable N rate while the other was conventionally preplant fertilized, applying a uniform rate across the field based on the field average. During the growing season, each field was monitored for nitrate leaching potential using ion exchange membrane technology. Soil and plant nutrient status were also monitored by collecting in-season petiole and soil samples at two key phenological stages, tuber initiation and tuber bulking. Overall this research showed that variable rate preplant N fertilizer management reduced N leaching potential during the early part of the growing season, but did not persist the entire season. Since preplant N accounted for only 40% of the total seasonal N applied, it is possible that further gains could be made with variable rate in-season N application or with variable rate water application.

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Teri A. Hale, Richard L. Hassell, Tyron Phillips and Elizabeth Halpin

Increased value of fresh sweet corn (Zea mays) during the last decade has lead to increased interest into the characteristics that increase marketability. Sweetness was examined over three phenotypes (su, se, and sh2) to determine if there was an optimum phenotype or cultivar within a phenotype. Each phenotype was isolated to prevent cross-pollinization. Cultivars were grown on sandy loam soil located at the Clemson University Coastal Research and Education Center (Charleston, S.C.). Early, mature, and late harvest dates were also evaluated to determine the optimal harvest date(s) for maximum flavor. High performance liquid chromatography was used to determine sucrose, fructose, glucose, and total sugars. Panelists' evaluation of sweetness and its acceptability significantly correlated with the high performance liquid chromatography analysis for sucrose and total sugars (sweetness, R = 0.70 and 0.61; acceptability, R = 0.64 and 0.55). Sucrose correlated with the total sugars (R = 0.95). As maturity increased, the ability of the taste panel to identify differences in phenotypes also increased. Although sucrose and total sugar levels were different between se, sh2, and su, taste panelists indicated no difference between se and sh2. Sh2 cultivars were considered sweet and acceptable on all harvest dates, but su was only acceptable to panelists at early maturity.

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Todd J. Cavins, John M. Dole and Vicki Stamback

Anemone (Anemone coronaria L.), snapdragon (Antirrhinum majus L.), larkspur [Consolida ambigua (L.) P.W. Ball & Heyw.], delphinium (Delphinium ×cultorum Voss.), sunflower (Helianthus annuus L.), lupine (Lupinus hartwegii Lindl.), stock [Matthiola incana (L.) R. Br.], and pansy (Viola ×wittrockiana Gams.) were grown in raised sandy loam ground beds in double-layered polyethylene-covered greenhouses which were either unheated (ambient) or had a 55 °F (13 °C) minimum night temperature in year 1 and 36 or 50 °F (2 or 10 °C) minimum night temperature in year 2. Results were species specific; however, the extreme low temperatures [21 °F (-6 °C)] in the unheated house limited delphinium and lupine production. The warmest greenhouses (55 and 50 °F) reduced production time for anemone, delphinium, larkspur, lupine (year 2), snapdragon (year 2),stock, and sunflower. The coolest greenhouses (unheated and 36 °F) increased stem lengths for anemone (year 2), delphinium, larkspur (year 1), lupine (year 2), snapdragon, stock, and sunflower. The coolest green-houses also yielded a profit or lower net loss for all species except delphinium, lupine, and snapdragon (year 2) for which profits were highest or net losses were lowest in the warmest greenhouses.

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Ken Tilt, Charles Gilliam, John Olive and Emmett Carden

Crape myrtle (Lagerstroe-mia L. × `Natchez'), live oak (Quercus virginiana Mill.), and Chinese pistachio (Pistacia chinensis Bunge) were planted into a sandy loam soil directly in the field or in grow-bags. Root and top growth were measured in March and July of the second year. Some of the trees were transplanted to 20-gal (76-liter) containers in March or July and grown for 3 months. Chinese pistachio developed a poor root system in field soil and was not ready for harvest in March or July. There was no difference in height, caliper, or top fresh weight for crape myrtle. Caliper and top fresh weight were similar for live oak trees. However, live oaks grown by traditional field production methods were taller than trees produced in grow-bags. With March transplanting, both crape myrtle and live oak trees from traditional field plantings were taller than trees transplanted from grow-bags 3 months after transplanting into containers. Tree top weight, caliper, and root ratings were similar for March-transplanted crape myrtle. Live oak trees transplanted from grow-bags had similar caliper and top weight but a higher root rating. July-transplanted crape myrtle trees had similar values for all variables 3 months later. All live oaks died when transplanted from traditional field plantings to containers in July. All live oaks grown in grow-bags survived transplanting.

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James W. Paterson

The effectiveness of varying rates and timing of applied primary plant nutrients as a completely soluble N-P-K fertilizer through a drip/trickle low volume irrigation system was studied during 1991 on eggplant (Solanum melongena cv. Harris Special Hibush). Before the drip irrigation tubing and black plastic mulch were laid on a coastal plain sandy loam soil, plots were treated with 0, 22, 45, and 67 kg ha-1 of nitrogen (N), phosphate (P2O5) and potash (K20). The higher rates of preplant fertilization did have a significant beneficial effect on total seasonal yields of quality eggplants. The preplant treatments also had an influence on mid and late season production. As the frequency of drip/trickle applied primary plant nutrients increased up to 6 seasonal applications, the total quality fruit production substantially increased. Frequency of applications also had an influence on seasonal yields. Applying increased rates of the primary plant nutrients at a low seasonal frequency of 3 applications had little influence on increasing total quality yields of eggplants. Individual quality fruit was significantly heavier from plants which received 5 to 6 applications of the soluble N-P-K fertilizer than from plants which received no fertilizer through the drip/trickle irrigation system for the season.

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Michael L. Parker and John R. Meyer

Peach trees (`Biscoe'/Lovell) were planted in March, 1988 in ten different ground cover management systems. The trees were planted at the Sandhills Research Station in Southeastern North Carolina on a Candor sand and Eunola sandy loam. In December, 1991 the trench profile method was used to evaluate root distribution under the six orchard floor management systems of nimblewill, bare ground control, centipedegrass, brome, bahiagrass, and weedy control. Trenches were dug parallel to the tree row 60 cm from the center of the row on both sides of the tree. Grids 1 meter square, sectioned into 10 cm squares, were placed on the profile walls and root distribution (in three size categories) was recorded for 1 meter on each side of the tree in each trench. Root numbers were greatly reduced under the vegetative covers that provided the greatest suppression of vegetative tree growth. Total root densities under the trees in the vegetative covers were ranked into three size categories which were correlated with the amount of vegetative tree growth.

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James L. Lasswell and Josiah W. Worthington

Field studies were conducted June 2, July 27, and October 15, 1988 to determine root concentrations within the dry and wetted soil of trickle-irrigated peach trees (Redglobe variety) in Windthorst fine sandy loam soil. Two “dryland” and four irrigation treatments (based on time of year irrigation initiated and previous irrigation history) were used. A single soil core sample 2.2 cm in diameter and 80 cm deep was taken 50 cm from trickle emitters on each of 8 trees per irrigation treatment and a single sample taken the same distance from the trunk on the “dry” side of the 8 trees in each dryland treatment. Each core was sectioned into 20-cm increments, washed, roots collected, separated (small, feeder roots; large suberized roots), dried and weighed.

Analyses of data for the small, feeder roots showed a significant difference (0.01 level) in root density between treatments, between sample times (each treatment), and with depth (each treatment). Root concentrations were highest in soils that had received irrigation in previous years and also when irrigation was initiated early in the year. Root concentrations were also found to be highest in the top 20 cm of soil regardless of treatment.

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Senay Ozgen, Mustafa Ozgen and Jiwan P. Palta

Several recent studies, including from our laboratory, have provided evidence that by improving tuber calcium level, we can improve tuber quality such as low internal defects and better storability. The purpose of this study was to be determine the influence of supplemental calcium fertilization on tuber size and tuber number. For this purpose, plantlets of Solanum tuberosum cv. Russet Burbank raised in tissue culture were planted in 20-L pots filled with sandy loam soil with pH of 6.9 and soil calcium level of 350 ppm. All treatments received same total amount of nitrogen (at the rate of 280 kg·ha–1). Five treatments were evaluated: i) nonsplit nitrogen (from ammonium nitrate), ii) split nitrogen (from ammonium nitrate), iii) split nitrogen + gypsum, iv) split nitrogen (from liquid nitrogen) + calcium chloride, and v) split nitrogen (from calcium nitrate). The total calcium was applied at the rate of 168 kg·ha–1. Gypsum application was made at 4 weeks after planting, and other sources of calcium were applied on a split schedule (equally split at 4, 6, 8 weeks after planting). Four months after planting, tubers were harvested and evaluated. In general, all calcium treatments had lower tuber number and greater tuber size compared to the nonsplit nitrogen control. The percentage of total A-grade tubers as well as the percentage yield from A-grade tubers was increased by all calcium applications. These results suggest that calcium content I the soil can influence both potato tuber number and tuber size.

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F.J. Peryea

Monoammonium phosphate (MAP) is a popular starter fertilizer in Pacific Northwest tree fruit orchards; however, its use on soils contaminated with lead arsenate pesticide residues can enhance As solubility, thereby increasing As phytoavailability. `Fuji'/EMLA.26 apple trees (Malus ×domestica Borkh.) were planted in Mar. 1992 on a lead arsenate—contaminated Cashmont gravelly sandy loam soil (HCl-extractable soil As range: 60-222 mg·kg-1) using in-hole starter fertilizer application of either MAP or ammonium sulfate at equivalent N and anion rates. In ensuing years, all trees received identical applications of ammonium nitrate only. Relative trunk cross-sectional area was inversely related to soil As concentration in the year of planting but not in subsequent years, and was independent of starter fertilizer treatment. Leaf and fruit As were positively related to soil As in all years. Leaf As was initially higher in the MAP-treated trees; however, this effect diminished over time and disappeared by 1995. Fruit As was independent of starter fertilizer treatment, and was substantially lower than the tolerance established for As in fresh produce. The experimental results indicate that MAP starter fertilizer can increase soil As phytoavailability to apple trees grown under field conditions; however, the effects on tree growth and food safety are insignificant.