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did not increase orchard productivity, nut yield, or quality. Wood (2009) suggested that moderate-width (2.4 m from the tree axis), short-cycle (annual or biennial pruning) mechanical hedging did not appear efficacious for southeastern pecan

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management practices for pollination ( Abu-Zahra and Al-Abbadi, 2007 ) and irrigation ( Ak and Agackesen, 2005 ) to maximize crop load ( Boler, 1998 ), trees still produce different fruit or nut sizes and quality in different years. This is a result, in part

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” years is biologically efficacious, but use in heavy crop-load “on” years appears to be without benefit to either nut yield or quality. Materials and Methods Orchard characteristics. The study orchard was located near Valdosta, GA, a humid climatic zone

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, equipment, and financial support; and Santa Cruz Valley Pecan Co., Sahuarita, Ariz., for assistance with the collection of nut quality data for the duration of this research. The cost of publishing this paper was defrayed in part by the payment of page

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. One method to combat alternate bearing and improve nut quality during large crop years is mechanical fruit thinning ( Smith and Gallott, 1990 ). Reid et al. (1993) demonstrated that fruit thinning while the fruit were between one-half and full ovule

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Pecan [Carya illinoinensis (Wangenh.) K. Koch] fruit presents a considerable weight for the tree to support during the growing season. A major part of this weight is due to the pecan shuck that surrounds the developing nut and kernel. Pecan clones vary considerably for the amount of shuck per nut, and little is known as to the value of this weight in determining final nut quality. Six cultivars differing in basic nut shapes and sizes were studied and found to vary greatly for shuck thickness, and weight of shuck per unit final nut weight and volume. Shuck thickness was shown to be a favorable genetic characteristic since fruit with thicker shucks had slightly greater nut fresh and dry weight, nut volume, nut density, kernel weight and content, and shuck weight per nut volume. `Sioux' had the thickest shucks (4.70 mm), while `Pawnee' had the thinnest shucks (3.72 mm). Fresh weight per fruit varied from 21.25 g for `Podsednik' to 10.18 g for Osage. Weight of fruit per tree was extrapolated using average shuck and nut weights, and it was determined that the fruit on each tree would weigh about 104 kg. This is a considerable weight, and adds substantially to limb breakage. However, thicker shucks contribute to final nut quality.

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Pecan tree (cv. “Western Schley”) water stress was numerically quantified with the crop water stress index (CWSI). The CWSI was used to schedule irrigation at increasing water stress levels to correlate the effects of water strees on tree growth, production, and nut quality from 1987 to 1989. Highest growth increases, production, and nut size were attained at lower water stress levels (CWSI = 0.08 to 0.14 units). Even moderate increases in water stress (CWSI>0.20 units) decreased pecan tree growth and production, and significantly reduced nut size (P=0.01). A significant difference (P=0.05) in nut quality was measured only in 1988. Depending on yearly climatic variation, the amount of irrigation water required to maintain the CWSI below 0.14 units in the same orchard varied 44% over three years. The CWSI is a viable tool to assess pecan water stress.

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Six years of previous research in a 12-year-old English walnut orchard, with a history of potassium deficiency, created a large number of trees with different potassium status. This provided the opportunity to study the long-term effects different potassium status has on English walnut trees growth, productivity, and nut quality. Walnut trees with a history of potassium deficiency, adequacy or luxury continued in this mode during this evaluation. Positive correlations existed between July leaf potassium levels and tree trunk sectional area (TCSA), visual potassium status, percent husk potassium, yield per tree, and tree yield per TCSA. These positive correlations suggest July leaf potassium levels of 1.4% to 1.5% as being adequate. This is higher than the 1.2% leaf potassium level currently recommended as being adequate for a July sample. Poor or no correlations existed between July leaf potassium levels and percent shell potassium, shell weight, shell breaking force, percent broken shell, nut size, nut weight, percent kernel potassium, percent light-colored kernels, percent edible kernel, percent kernel yield, or percent shriveled kernel. Trees with leaf potassium levels at or above 1.5% July leaf potassium produced 80 pounds per tree more yield than trees with leaf potassium levels at or below 1.0% July leaf potassium levels. These data indicate that good tree potassium status influences tree size and tree productivity. Also the walnut husk is an important sink for the accumulation of potassium. Currently recommended adequate potassium levels for walnut appear to be lower than what this study indicates.

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The nuts of 10 pecan cultivars were used to produce rootstock trees for the propagation of two scion cultivars—Posey and Pawnee. Seed sources included: `Chickasaw', `Colby', `Dooley', `Giles', `Greenriver', `Major', `Mohawk', `Peruque', `Posey', and `Shoshoni'. Leaf analysis performed in 1994 and 1996 revealed that rootstock influenced K and Zn concentrations. Scions propagated on `Posey' seedlings contained the greatest amount of K, while scions propagated on `Greenriver' seedlings contained the least. Zn levels were highest in trees with `Chickasaw' seedling rootstocks and the least in `Major' seedlings. Yield and nut quality was influenced by a major drought during the late summer and fall of 1995. Nuts produced by trees with `Chickasaw' and `Colby' rootstocks had the highest kernel percentage, while trees grown on `Major' and `Posey' had the lowest. The greatest yields, during the drought year, were produced from scion cultivars grafted on `Giles' and `Chickasaw' seedling rootstocks. `Major' and `Greenriver' seedlings produced trees with the smallest yields.

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Abstract

Leaf to fruit ratios of 2, 4, 8, and 12 were created on girdled shoots of three cultivars of pecan (Carya illinoensis (Wangenh.) C. Koch). Girdling of fruiting and vegetative shoots reduced net photosynthesis to nearly 30% and 3%, respectively, of the ungirdled “checks.” Differences in photosynthetic rates among the various leaf to nut ratios were not detectable. Two leaves, equivalent to 575 cm2 of leaf area, were sufficient to fill one pecan kernel of ‘Sioux’ or ‘Western’. A ‘Mohawk’ leaf to fruit ratio of 4 produced nuts superior in quality to those supported by two leaves. Girdling tended to increase shoot carbohydrates, and starch accumulation was related to leaf to fruit ratio in ‘Mohawk’.

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