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
Bruce W. Wood
” 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
Donald J. Garrot Jr., Michael W. Kilby, Delmar D. Fangmeier, Stephen H. Husman and Andrew E. Ralowicz
, 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
Charles T. Rohla, Michael W. Smith and Niels O. Maness
. 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
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.
D.J. Garrot Jr., M.W. Kilby, D.D. Fangmeier and S.H. Husman
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.
Laurence Sistrunk, Dan Chapman and J. Benton Storey
Four cultivars of pecan [Carya illinoinensis (Wangenh.) K. Koch] were selected for the study (`Cheyenne', `Mohawk', `Pawnee', and `Osage'). The influence of total climatic heat units, during nut filling, on nut quality was compared from 14 geographic locations over a 3-year study. Nut quality parameters included nut size by weight, kernel percentage by weight, kernel color by Hunter Color Difference Meter, fatty acid profile by GC, and total oil by NMR. Nuts were harvested at shuck split, dried to 3% moisture, and stored at –20C prior to analysis. Monounsaturated fatty acids (MUFA) and total oil increased, and polyunsaturated fatty acids (PUFA) decreased in `Mohawk' 2 out of 3 years with increased heat units. Fatty acids in `Pawnee' responded the same as in `Mohawk' in 1992, but were variable in 1991. In 1993, `Pawnee' kernel whiteness and total oil decreased with increased heat units. Higher heat units caused the testas of `Cheyenne' to be darker in all 3 years. MUFA of `Cheyenne' increased with increased heat units 1 out of 3 years. The PUFA content of `Cheyenne' decreased with increased heat units in 1993. `Osage' showed a reversal of MUFA and PUFA with increased heat units. High negative correlation between oleic and linoleic acid were obtained for all cultivars.
William H. Olson
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.
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.
Qiupeng Zeng, Patrick H. Brown and Brent A. Holtz
A field experiment was conducted from 1996 to 1998 to examine the effects of K fertilization on leaf K, nut yield, and quality in pistachio (Pistacia vera L.). There were six treatments, including four annual rates of K application (0, 110, 220, and 330 kg·ha-1) and three K sources (K2SO4, KCl, and KNO3). Pistachio trees exhibited highly fluctuating seasonal leaf K levels. Leaf K concentration was low (<10 g·kg-1) during spring flush, increased dramatically during fruit development, and declined rapidly after harvest. Leaf K concentration increased following K fertilization. Potassium fertilization at the rate of 110 to 220 kg·ha-1 K significantly increased nut yield and quality, but nut yield tended to decrease when the annual rate exceeded 220 kg·ha-1 K. There were no significant differences among the K sources in their effects on leaf K concentration, nut yield, and quality. The use of KCl as a K source for 3 years did not increase leaf Cl concentration. There was a significant, positive correlation between nut yield and leaf K concentration during nut fill. The critical leaf K value for optimal pistachio production determined from 3 years' cumulative data was 16.9 g·kg-1. For sustained production in highly productive pistachio orchards, we recommend annual application rates of 110 to 220 kg·ha-1 K, using K2SO4, KCl, or KNO3.