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Abstract
Many pecan groves throughout the south are grazed for pasture. Simazine at 3 lb/A is recommended for pastures, but the amount of residue accumulating in pecan nuts grown in pastures treated with this herbicide is not known. In this study rates of 0, 1, 2, 4, and 8 lb/A of active Simazine was applied as a spray underneath the canopy of approximately 40-year old Stuart pecan trees on March 16, 1963 while trees were dormant. Two replications were used. On November 14, a 10 lb nut sample was collected from each tree and analyzed by the Geigy Research laboratories. All samples contained less than 0.04 ppm of Simazine in both shells and kernels, which is considered essentially no residue. No damage to the trees was noticed.
Yield and quality of pecan nuts were as high when 50 pounds N/acre was applied through a dripirrigation system as with 100 pounds/acre (112 kg·ha−1) applied either all broadcast or half broadcast-half fertigated. All N treatments kept leaf N well above the 2.50% (dry weight) lower threshold recommended for pecans. The 50 pounds N/acre-all-fertigated treatment resulted in less soil pH reduction and less loss of K, Ca, and Mg from soil in the nonwetted zone underneath the tree canopy than broadcast treatments. Soil pH, K, and Mg were slightly lowered in the 6- to 12-inch (15 to 30 cm) soil layer when all of the N was fertigated. Higher leaf Ca and Mg from the low rate of N fertigated reflected the higher concentrations of these elements in the soil in the nonwetted zone rather than the lower concentrations in the wetted zone. There was no evidence of a detrimental effect on the tree from lowering the N application to only 50 pounds/acre and applying it in four monthly applications through the drip irrigation system beginning 1 Apr.
Fifteen pecan (Carya illinoinensis) genotypes were evaluated over a period of 20 years in a test orchard located near Tifton, Ga. Genotypes tested included seedling selections (`Candy', `Maramec', `Melrose', `Moreland', `Sumner', and `Western Schley'), USDA releases (`Creek', `Kanza', `Kiowa', and `Pawnee'), and USDA selections (USDA 41-19-20, USDA 53-11-139, USDA 53-9-1, USDA 57-7-22, and USDA 64-11-17). Actual yields were measured for each tree in the test throughout the test period and the alternate bearing intensity (I) of each cultivar was calculated. Average annual nut production in years 1 to 10 ranged from 19 lb (8.6 kg) in the precocious cultivar `Candy' to 6 lb (2.7 kg) in the nonprecocious cultivar `Melrose'. Although a wide variation was seen in the average yield of clones in years 11 to 20, differences were not significant. A subsample of nuts was taken for each tree annually and percent kernel, nuts/lb, specific gravity, and nut volume were determined. Significant differences were found between clones for each of these traits. Most clones were not acceptable for commercial use in Georgia due to small nut size, poor kernel quality, or excessive alternate bearing. Recommended clones include: `Pawnee', which produced large nuts of excellent quality with an early harvest date, `Sumner', which produced large nuts of moderate quality with a late harvest date, and `Kiowa', a precocious bearer of large, good-quality nuts.
After 10 years, application of 112 kg N/ha, divided into four annual applications and applied through the drip irrigation system (fertigated), provided nut yield and quality as good as 224 kg·ha–1 all broadcast or 1/2 fertigated and 1/2 broadcast. Leaf N was well above the 2.50% deficiency threshold. Treatment rates were halved for six additional years with no detrimental effects on yield and quality from fertigation. All treatments still provided leaf N well above the deficiency threshold. After 16 years of N fertigation there appears to be no serious reduction of pH or flushing of other nutrients from the wetted zone of the emitter. Leaf and soil analysis indicate a loss of Ca and Mg in the area away from the emitter when N was broadcast. Soil pH and nutrients were lower in the wetted zone of the emitter than in the area not wet by the emitter, and soil pH, K, and Mg were reduced in the 15- to 30-cm layer with fertigation. Leaf nutrient concentrations reflected the cation concentrations in the nonwetted area. Broadcast N was from NH4NO3 and fertigated N was from URAN (16% N from NH4NO3 and 16% N from urea).
Abstract
‘Woodard’ pecan (Carya illinoensis (Wang.) K. Koch) is an exceptionally thin-shelled nut of high percentage kernel for the inshell trade.
Abstract
Mature pecan, Carya illinoensis (Wang.) Koch., grove management systems of 1) rotational summer grazing, 2) clean cultivation + winter legume, 3) winter or spring intercropping + summer cultivation, and 4) closely mowed sod affected yields differently in different years, but did not affect total yield or tree growth significantly over a 10-year period. Kernel quality, nuts/kg count, nut size, and tree growth were not affected consistently by management systems. Extra fertilization, particularly N, applied to grazed and intercropped plots reduced soil pH and residual soil K; but treatments affected soil P very little. Leaf Zn and Mn were also high for these treatments. Applied N, or N from legumes, was reflected in higher leaf N. Leaf K, Mg, Fe, B, Cu, Al, Mo, and Sr were not affected significantly by management treatment.
Abstract
Field data indicate that part of the K requirement for sweet potatoes (Jpomoea batatas Lam.) may be satisfied by Na without reducing yields or quality, but high rates of substitution reduced yield in some years. Significant reduction in leaf K occurred with increased substitution by Na. Sweet potatoes readily absorbed Na with leaf Na increasing as Na application increased.
Abstract
A longitudinal splitting of pecan which causes loss of nuts of thin-shelled cultivars during the “water” stage of the kernel is described. A similar splitting was induced by forcing water into the nut with a hypodermic needle. Soaking of nuts in water either on or off the trees did not induce splitting.
Alternate bearing is a major economic problem for producers of pecan nuts [Carya illinoinensis (Wangenh.) K. Koch], yet a fundamental understanding of alternate bearing remains elusive. Nut yields (over a period of up to 78 years) from a commercial-like orchard of 66 cultivars was used to calculate alternate bearing intensity (I). Best-fit regression analysis indicates no association between I and fruit ripening date (FRD) or nut volume; although, there was moderate association with post-ripening foliation periods (PRFP) in that I tends to decrease as the length of the PRFP decreases. Multiple regression models indicated that FRD and nut volume were poor predictors of I: however, PRFP possessed significant inverse predictive power. Late-season canopy health, as measured by percentage of leaflet retention, decreased as FRD approached early-season ripening. Late-season photoassimilation rate was high er on foliage of trees with late FRDs than those with mid- or early-season ripening dates. These data provide new insight into the complex nature of alternate bearing in pecan and provide evidence for modifying the existing theories of alternate bearing of pecan.