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K.R. Woodburn and J.R. Clark

Flower cluster thinning effects were investigated on A-2274, a large-fruited, seedless table grape selection from the Univ. of Arkansas Grape Breeding Program. The objective of the study was to evaluate flower cluster thinning as a method to enhance cluster size and fill. Treatments included thinning to one flower cluster per shoot, removing one-half of each cluster, and a control (no flowers removed). Each treatment consisted of three, single-vine replications, with each vine being pruned to 32 buds. Removal of entire flower clusters (to one per shoot) resulted in larger clusters and a trend toward higher cluster fill ratings. Berry mass, number of clusters per vine, and yield per vine were unaffected by flower cluster treatment. Berries per cluster were reduced by the partial flower cluster removal treatment. Flower cluster thinning to one cluster proved a beneficial practice in increasing cluster characteristics of this promising selection.

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J.R. Clark and J.N. Moore

Two new seedless grape cultivars were released in 1999 from the grape breeding program at the Univ. of Arkansas. `Jupiter' is the fifth release from the program. `Jupiter' is blue-fruited, has large berries, non-slipskin texture, and a mild muscat flavor. Yields of `Jupiter' were very good in replicated trials, and hardiness is also adequate for production in all areas of the South. `Jupiter' ripens 5 days later than `Venus', but earlier than `Mars' or `Reliance'. `Neptune' is the sixth release and first white-fruited cultivar from the program. It has medium-sized berries, large clusters, non-slipskin texture, and a mild, fruity flavor. Yields of `Neptune' were moderate in replicated trials. `Neptune' ripens 17 days later than `Venus' and 3 days earlier than `Mars'. Both cultivars were developed and evaluated with a commercial cultural system including routine fungicide applications, and fungicides will be required to reliably produce these cultivars. Neither of these cultivars has been tested in a Pierce's Disease region of the United States, and it is not anticipated that either will have resistance to this disease.

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J. Naraguma, J.R. Clark, and R.J. Norman

A spring application of 19 g CO(15NH2)2/plant at 2.49% atom percent enrichment was made in Mar. 1995 on 2-year old, field-grown `Arapaho' blackberry plants. Individual plants were harvested during the study at preharvest (late May), postharvest (mid-July), and early dormancy (late October). The following plant parts were separated for analysis: roots, primocanes, floricanes, primocane leaves, floricane leaves, fruits. Soil samples were also taken from within the drip line of the plants at each sample date. Plant tissues were washed, dry weights measured and ground for acid digestion, total N determination and 15N analysis. Samples were measured for 15N atom percent abundance by a isotope ratio spectrometer. The whole-plant dry matter in creased during the season from 53 g in May to 153 g in October. Plants sampled in October had a greater amount of dry matter in roots than in any other tissue. There was a decreased total N content in all vegetative tissues (leaves and canes) from May to October. The maximum fertilizer 15N percent recovery was 43% (October) and the minimum was 12% (May) from the total plant tissues. Compared to other plant tissues, floricane leaves and primocanes recovered significantly more fertilizer 15N in May, while roots and primocane leaves recovered more in October. Floricanes and fruits did not increase in 15N levels during the sampling period. Fertilizer 15N recovered in the soil amounted to 35.5% of the applied with 4.5% found in the inorganic fraction, 31% in the organic fraction. There were no statistical differences in percent recovery of the fertilizer 15N among sample dates in the topsoil. October 15N percent recovery was much lower than May in the subsoil, indicating a downward movement of N by leaching. Averaging all sample dates, 59.5% of the labeled fertilizer was accounted for in the plant and soil, with the remaining portion probably lost via volatilization, leaching, and/or denitrification.

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John R. Clark and Paul J. Sandefur

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John R. Clark and Paul. J. Sandefur

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John R Clark and J.N. Moore

Blue Ridge, Cape Fear, Georgiagem, and O Neal southern highbush blueberry cultivars were grown for 5 years on a fine sandy loam soil in a comparison of plants either mulched with uncomposted pine sawdust and woodchips or nonmulched. Other cultural practices were identical and all plants received the same amount of trickle irrigation. A significant mulch × cultivar interaction for yield and mulch × plant age interactions for yield, individual berry weight, and plant volume were found. Cape Fear was the highest-yielding mulched cultivar, followed by Blueridge, Georgiagem, and O Neal. Mulched plants had higher yields and produced larger plants. Average individual berry weight was greater for mulched plants in the first year of harvest, but not different among treatments in other years. The data reveal that these southern highbush cultivars performed similar to northern highbush (Vaccinicum corymbosum L.) in their need for mulching for adequate production on upland soils.

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J.R. Clark, J. Naraguma, and R.A. Allen

A planting of sawdust-mulched highbush blueberries (cv. Bluecrop) was established on a Captina silt loam at the Univ. of Arkansas Research and Extension Center, Fayetteville, in 1994. Nitrogen rate and method of delivery treatments were begun that year and continued through the first two fruiting years (1996 and 1997). Rates included 0, 67, 134, 201, and 268 kg·ha-1 N using ammonium sulfate during the fruiting years (one-half and two-thirds these rates in 1994 and 1995, respectively), and methods of delivery included dry, surface-applied, and fertigation. Total N for the year was applied in three applications for the dry application and in 12 applications using fertigation. Neither yield nor berry mass were statistically significantly affected by N rate or method of delivery. Also, method of delivery had little effect on foliar levels of any macro- and microelements. Rate of N influenced foliar N most years, with the highest N rate increasing foliar N the greatest. The N rate required to consistently achieve adequate foliar N levels (minimum of 1.6% N) was 134 kg·ha-1. Foliar levels >2.0% were common with the two highest N rates. Foliar Mg and Mn were also influenced by N rate, with the lowest Mg level found for the highest N rate, while excess foliar Mn (800 to 100 ppm) was common with the higher N rates in 1997.

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L.R. Costello, N.P. Matheny, and J.R. Clark

Since it is unlikely that crop coefficients will be established for landscape plantings, a method to estimate landscape water requirements is proposed. By evaluating three factors that significantly influence water use-species planted, vegetation density, and site microclimate-and assigning numerical values to each, an estimate of a landscape crop coefficient (or landscape coefficient, KL) can be calculated. An estimate of evapotranspirational water loss for landscapes is then the product of the landscape coefficient multiplied by the reference evapotranspiration. This paper presents values for the above three factors and discusses the rationale for each. Examples using the landscape coefficient formula are included, as well as a discussion of special considerations relative to its use.

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J.N. Moore, John R. Clark, and Justin R. Morris

The impending release of a new blackberry cultivar and a new grape cultivar by the University of Arkansas Agricultural Experiment station will be discussed. The blackberry, tested as A-1536, is an erect, thornless type ripening two weeks before 'Navaho'. It produces very firm, highly flavored fruit similar to 'Navaho'. The grape, tested as A-1335, is a blue-seeded juice grape with good adaptation to areas with high summer temperatures where 'Concord' does not ripen evenly. Fresh fruit and processed juice quality has been rated equal to or better than 'Concord' juice for quality attributes.

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P. Perkins-Veazie, J.K. Collins, and J.R. Clark

The storage life of blackberry fruit is generally `2 to 3 days when stored at 1C. This study was done to determine the maximum storage life among erect blackberry cultivars, and to determine storage temperature effects on storage life. Shiny black fruit from `Navaho', `Arapaho', and `Shawnee' cultivars were stored at 2C, 5C, or 10C for 20, 14, and 7 days, respectively. At any temperature. only 10-20% of `Navaho' fruit had decay, while 30-50% of `Arapaho' and 40-70% of `Shawnee' fruit had decay. Weight loss was 3-5% depending on temperature and was not different among cultivars. Soluble solids concentration did not change during storage but titratable acidity decreased in all cultivars for fruit held at all temperatures. Anthocyanin content increased during storage in `Shawnee' and `Navaho' but not in `Arapaho' fruit. Results indicate that `Navaho' fruit have a longer shelflife than other blackberry cultivars.