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Salo Ponchner and R.M. Carlson

Effects of crop load and potassium on seasonal trends in root starch concentrations were studied in a commercial orchard. Treatments were a factorial combination of fruit thinning and potassium fertilization. Root samples were divided into <10mm and >10 mm diameter categories. Large crop load was associated with lower starch concentrations in the >10 mm roots after stage III of fruit growth. Highest root starch concentrations occurred in low crop trees that had been fertilized with potassium. Roots <10mm diameter also accumulated starch throughout the season but the concentrations were much lower than found in the >10 mm roots and there was little difference among treatments at any sampling date. On the basis of these results, roots >10mm appear to be more important than smaller roots as storage organs and therefore are more affected by stresses and competition with other organs. Continuation of the project will seek relationships between early season root starch concentrations and tree performance including alternate bearing.

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J. A. Rivers, R.O. Miller and R.M. Carlson

Ornamentals, fruit and vegetable crops are commonly tested for inorganic anions, NO3-N, PO4-P, Cl and SO4-S, to identify the nutritional status of the plant. Two percent (0.20 M) acetic acid has primarily been used as the extractant for these inorganic anions. The use of acetic acid does not quantitatively extract SO4-S and PO4-P. Research using calcium formate was initiated to assess its effectiveness as an universal extractant for inorganic anions. Results of a series of experiments will be presented identifying the optimum calcium formate concentration, extraction time, and extractant sample ratio for quantitative removal and measurement of NO3-N, PO4-P, Cl and SO4-S. Results of spiking experiments will be presented using a range of horticultural crops important to California agriculture. Additional data will be presented on the use of calcium formate for the determination of K and NH4-N in botanical tissues.

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M. Lenny Wells, D. Scott Carlson and R. Philip Edwards

The effects of mechanical fruit thinning on pecan [Carya illinoinensis (Wangenh.) K. Koch] yield, nut quality, and profitability were assessed using ‘Sumner’ and ‘Cape Fear’ pecan trees cultivated in a commercial orchard. The moderate to light production year (OFF year) return crop and return crop value of ‘Cape Fear’ and ‘Sumner’ was increased by mechanical thinning in the year of high production (ON year). This enhanced the 2-year total value and 2-year average value of both cultivars. Increased profitability of these cultivars with mechanical fruit thinning results primarily from higher yields and prices in the OFF year of production, which offset any loss in yield and/or crop value generated by fruit thinning in the ON year. Premature germination of ‘Cape Fear’ pecans was reduced from 34% to 4% with mechanical fruit thinning. Mechanical fruit thinning appears to be a highly valuable practice, leading to increased profit potential for ‘Cape Fear’ and ‘Sumner’ pecan.

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F.J.A. Niederholzer, R.M. Carlson, K. Uriu, N.H. Willits and J.P. Pearson

A study was undertaken to determine the seasonal dynamics of leaf and fruit K content and the influence of tree K status and fruit growth on leaf and fruit K accumulation rates in French prune (Prunus domestics L. cv. d'Agen). Mature trees in a commercial orchard were treated with various rates of K2 SO4. (O to ≈20 kg/tree) in the fall. Fruit dry weight yield per tree at harvest and fruit K content were higher for high-K trees, but fruit percent K (by dry weight) was ≈1.0% for all trees. Leaf scorch and subsequent abscission severely reduced the canopy of K-deficient trees. Significant positive linear relationships between leaf and fruit K accumulation rates existed for the periods of 28 Apr.-28 May (May) and 28 May-7 July (June). A significant negative linear relationship existed between these two criteria from 7 July-3 Aug. (July). May (0.237 mg K per fruit-day) and July (0.267 mg K per fruit-day) mean fruit K accumulation rates were similar, but both were significantly higher (P = 0.001) than those for June (0.140 mg K per fruit-day). Mean leaf K accumulation rates for May (- 0.007 mg K per leaf-day) and July (-0.010 mg K per leaf-day) were similar, but both were significantly (P = 0.001) less than for June (0.005 mg K per leaf-day). Potassium per fruit accumulation was highest in trees with highest K status. Periods of net leaf K efflux and influx did not precisely correlate with fruit growth stages measured by fruit dry weight. The period of lowest fruit K accumulation (28 May-7 July) coincided with the period of maximum dry matter accumulation by the kernel. After 7 July, all increases in fruit dry weight and K content were due to mesocarp growth.

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S.A. Weinbaum, F.J.A. Niederholzer, S. Ponchner, R.C. Rosecrance, R.M. Carlson, A.C. Whittlesey and T.T. Muraoka

Four adjacent heavily cropping 12-year-old `Petite d'Agen' prune (Prunus domestica L.) trees were selected, and two of the trees were defruited in late spring (28 May) after the spring growth flush and full leaf expansion. Trees received K daily through the drip-irrigation system, and 15N-depleted (NH4)2SO4 was applied twice between the dates of defruiting and fruit maturation. Trees were excavated at the time of fruit maturity (28 July) and fractionated into their component parts. The following determinations were made after tree excavation and sample processing: tree dry weight, dry weight distribution among the various tree fractions (fruit, leaves, roots, trunk, and branches), tree nutrient contents, within-tree nutrient distribution, total nonstructural carbohydrates (TNCs), and recovery of labeled N. Trees only recovered ≈3% of the isotopically labeled fertilizer N over the 6-week experimental period. Heavily cropping trees absorbed ≈9 g more K per tree (17% of total tree K content) during the 2-month period of stage III fruit growth than defruited trees. The enhanced K uptake in heavily cropping trees was apparently conditioned by the large fruit K demand and occurred despite greatly reduced levels of starch and TNCs relative to defruited trees. Fruit K accumulation in heavily cropping trees was accompanied by K depletion from leaves and perennial tree parts. Except for K, fruited and defruited trees did not differ in nutrient content.

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Erin M.R. Clark, John M. Dole, Alicain S. Carlson, Erin P. Moody, Ingram F. McCall, Frankie L. Fanelli and William C. Fonteno

Each year a wide variety of new cultivars and species are evaluated in the National Cut Flower Trial Programs administered by North Carolina State University and the Association of Specialty Cut Flower Growers. Stems of promising and productive cultivars from the National Trial Program were pretreated with either a commercial hydrating solution or deionized (DI) water and placed in either a commercial holding solution or DI water. Over 8 years, the vase life of 121 cultivars representing 47 cut flower genera was determined. Although there was cultivar variation within each genus, patterns of postharvest responses have emerged. The largest category, with 53 cultivars, was one in which a holding preservative increased vase life of the following genera and species: acidanthera (Gladiolus murielae), basil (Ocimum basilicum), bee balm (Monarda hybrid), black-eyed susan (Rudbeckia hybrids), campanula (Campanula species), celosia (Celosia argentea), common ninebark (Physocarpus opulifolius), coneflower (Echinacea purpurea), coral bells (Heuchera hybrids), feverfew (Tanacetum parthenium), foxglove (Digitalis purpurea), ladybells (Adenophora hybrid), lisianthus (Eustoma grandiflorum), lobelia (Lobelia hybrids), obedient plant (Physostegia virginiana), ornamental pepper (Capsicum annuum), pincushion flower (Scabiosa atropurpurea), pinkflower (Indigofera amblyantha), seven-sons flower (Heptacodium miconioides), shasta daisy (Leucanthemum superbum), sunflower (Helianthus annuus), snapdragon (Antirrhinum majus), sweet william (Dianthus hybrids), trachelium (Trachelium caeruleum), and zinnia (Zinnia elegans). Hydrating preservatives increased the vase life of four basils, coral bells, and sunflower cultivars. The combined use of hydrator and holding preservatives increased the vase life of three black-eyed susan, seven-sons flower, and sunflower cultivars. Holding preservatives reduced the vase life of 14 cultivars of the following genera and species: ageratum (Ageratum houstonianum), false queen anne's lace (Ammi species), knotweed (Persicaria hybrid), lisianthus, pineapple lily (Eucomis comosa), sneezeweed (Helenium autumnale), yarrow (Achillea millifolium), and zinnia. Hydrating preservatives reduced the vase life of 18 cultivars of the following genera and species: feverfew, lisianthus, ornamental pepper, pineapple lily, seven-sons flower, shasta daisy, sneezeweed, sweet william, sunflower, trachelium, yarrow, and zinnia. The combined use of hydrating and holding preservatives reduced the vase life of 12 cultivars in the following genera and species: false queen anne's lace, feverfew, pincushion flower, sneezeweed, sunflower, trachelium, yarrow, and zinnia. Data for the remaining 50 cultivars were not significant among the treatments; these genera and species included beautyberry (Callicarpa americana), black-eyed susan, blue mist (Caryopteris clandonensis), calendula (Calendula officinalis), campanula, cleome (Cleome hasserliana), common ninebark, dahlia (Dahlia hybrids), delphinium (Delphinium hybrids), flowering peach (Prunus persica forma versicolor), heliopsis (Heliopsis helianthoides), hemp agrimony (Eupatorium cannabinum), himalayan honeysuckle (Leycesteria formosa), hydrangea (Hydrangea paniculata), larkspur (Consolida hybrids), lily of the nile (Agapanthus hybrid), lisianthus, lobelia, ornamental pepper, pineapple lily, scented geranium (Pelargonium hybrid), sunflower, sweet william, and zinnia.