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  • Author or Editor: R. M. Carlson x
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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.

Free access

Abstract

Nutrient solution experiments were conducted to characterize the absorption of K+ and NH 4 + , as affected by plant K+ status and solution concentrations of K+ and NH 4 + , for tomato (Lycopersicon esculentum Mill. cv. UC823) and ‘French’ prune scions (Prunus domestica L.) on Myrobalan 29C rootstocks (P. cerasifera Ehrh.). Prune and tomato plants pretreated in solutions adjusted daily to 1000 μm K+ had significantly higher K+ concentrations in leaves and roots than those plants pretreated in nutrient solutions adjusted on alternate days to 100 μm K +. NO differences in total N concentrations of roots or leaves due to pretreatment were detected. Potassium uptake rates of prune and tomato plants of high K+ status were significantly lower than those of low K+ status. For both plant species, NH 4 + uptake by roots was independent of plant K+ status. On a relative basis, the presence of solution NH 4 + inhibited K+ uptake to a greater extent in K+-loaded plants than in K + -starved plants. Potassium status of the plant had no effect on the extent of NH 4 + uptake inhibition due to solution K +. Ammonium-induced efflux of K+ from plant roots to initially K+ -free solutions was greater from roots of high K+ status than from roots of low K+ status. Increasing solution NH 4 + concentrations from 100 μm to 1000 μm significantly lowered the K+ uptake rates. The effect was much more dramatic in prune than in tomato. Increasing solution K+ concentrations from 100 μm to 1000 μm had no significant effect on the NH 4 + uptake by either plant species.

Open Access

Abstract

A sample of clinoptilolite with an exchangeable K, Na, Ca and Mg content of 160.0, 33.5, 18.7, and 0.4 meq/100 g was evaluated as a slow-release К fertilizer by leaching and growth studies of Chrysanthemum morifolium, Ramat. Potassium release from an amended potting medium indicated that clinoptilolite did not behave like a soluble K source but was very similar to slow-release fertilizers. A single application of 50 g clinoptilolite per 1.5 liters of potting medium produced 3-month chrysanthemum yields equal to those obtained with a daily irrigation with 234 ppm K.

Open Access

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.

Free access

Abstract

A greenhouse screening system was developed with ‘Curtis’ seedlings of ‘Curtis’ pecan (Carya illinoensis (Wang) K. Koch) to test the effect of Ca in reducing defoliation caused by foliar applications of (2-chloroethyl)- phosphonic acid (ethephon). Ethephon alone at 2000 ppm induced 100% abscission, but the effect could be offset with 0.01 M Ca from several sources. The added Ca increased the freely available Ca in treated leaves. As pH of the solutions containing ethephon alone increased from 2.0 to 8.0, less defoliation occurred.

Open Access

Abstract

Leaves and stems from bearing and non-bearing branches of French prune (Prunus domestica L. cv. Agen) were collected periodically during the growing season and analyzed for their carbohydrate and mineral contents. The non-bearing shoots contained more starch than the bearing ones during the period when the fruits were growing rapidly and accumulating soluble solids. The % dry matter and alcohol insoluble substances (AIS) were also higher in the former than those of the latter. Analysis of fruits revealed that sorbitol was the predominant carbohydrate, followed by sucrose and reducing sugars during the ripening period. These findings indicate that when internal competition for carbohydrates becomes limited, the stem cells assimilate constituents, presumably cell wall substances, other than reserve food. Leaf analysis also reflected the diminished competition in that the dry matter, sugar and starch contents were consistently higher in leaves from non-bearing limbs than those collected from bearing ones on a unit area basis. No difference was detectable in mineral contents of leaves and stems collected from de-fruited and bearing limbs.

Open Access

Abstract

Although premium wine grapes (Vitis vinifera L.) are planted in soils of low P availability, there is little knowledge of P requirements and of the appropriate methods of P analysis in grapevines. Therefore, acetic acid extractable P was investigated as a method for determining grapevine P status. Analysis of absorption spectra established that absorbance peaks at 710 or 882 nm of the phosphomolybdate complex formed in acetic acid extracts of grapevine tissues can be used for analysis of P status. Acetic acid-extractable P was independent of sample size and extraction time and was linearly related (r 2 = 0.96) to total P in four premium wine grape varieties. Lamina indicated whole plant P status better than petioles, since extractable P accumulated more in lamina than in petioles. Total and extractable P of basal lamina decreased significantly after anthesis, which diminished the differences between P-sufficient and P-deficient vines. Therefore, the best time to assess vine P status using leaves is at anthesis. When P fertilizer was applied, lamina-extractable P was positively correlated with berry weight, yield, and pruning weight in Chenin blanc vines growing under P-deficient conditions. The results indicate that acetic acid extractable P in lamina sampled at anthesis is a sensitive measure of grapevine P status.

Open Access

Abstract

Flower petal abscission (shattering) in seed geraniums (Pelargonium X hortorum Bailey) is delayed by low temperature (1-5°C) and ethylene-free air. Naphthaleneacetic acid (NAA) or CO2 (5%) did not delay shattering. Respiration and endogenous ethylene synthesis did not follow a climacteric pattern. A method was devised to test flowers for petal abscission. Variation in petal abscission was found among flowers of 35 cultivars evaluated over a 2-year period.

Open Access

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.

Free access

Abstract

Abscission of inflorescence buds increased progressively as leaf area decreased or number of nuts per branch increased. The data strongly indicate that dominance of the developing seed over the inflorescence buds in competition for carbohydrates might be responsible for bud abscission. However, the possible involvement of a hormone(s) originating in the leaves should not be overlooked.

Open Access