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Esteban A. Herrera

Pecan [Carya illinoensis (Wangenh.) K. Koch] fruit development was evaluated over three growing seasons (1981-83) to determine the seasonal growth patterns in the cultivars Ideal and Western. Gross morphological stages were examined weekly in fruit dissected in cross and longitudinal sections. Free-nucleate endosperm was first observed in mid-July when fruit had grown to 50% of their final length, occurring at 67 days after stigma receptivity (DASR) for `Ideal' and 76 DASR for Western'. Maximum content of free-nucleate endosperm occurred 100 DASR in `Ideal' and 109 DASR in Western' fruit. Ovary wall Signification was completed 119 DASR in `Ideal' and 132 DASR in `Western'. At this time, nut enlargement was complete. Cotyledon thickening required 36 and 43 days for `Ideal' and Western', respectively. The time from stigma receptivity to completion of cotyledon thickening in mid-October was 13 days longer for Western' than for `Ideal'. Because of a cool spring in 1983, all stages required a longer time in 1983 than in the previous 2 years. Most aspects of fruit development were similar between `Ideal' and Western' over the 3-year study.

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Esteban A. Herrera

Almost 58,000 acres of pecans [Carya illinoinensis (Wangenh.) K. Koch] are planted in the western United States, which includes western Texas and southern areas of New Mexico, Arizona, and California. `Western Schley' is the main cultivar planted, with `Wichita' trees used as pollenizers. All orchards are flood-irrigated and almost no diseases are present. The pecan aphid complex is the predominant insect problem; however, orchard crowding is becoming a problem, and growers are thinning orchards and transplanting trees to new sites.

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Esteban A. Herrera

`Western Schley' pecans [Carya illinoinensis (Wangenh.) K. Koch] were evaluated for flavor by a 17-person sensory panel after oven-drying nuts that had been harvested 1 to 7 weeks before normal harvest in 1985. The nuts were 1) not dried, 2) oven-dried 24 hours at 29C, 3) oven-dried 24 hours at 35C, 4) oven-dried 30 hours at 29C, 5) oven-dried 30 hours at 35C, 6) dried at room temperature for 72 hours, and 7) collected at normal harvest time (control). At the start of the experiment, kernel moisture was ≈ 14%. Some of the treatments reduced kernel moisture to <5 % the first week of the experiment, but drying nuts at room temperature for 72 hours reduced kernel moisture as effectively as other treatments. Judging by kernel flavor, pecans can be harvested ≈ 4 weeks before normal harvest (performed after the first freeze in Las Cruces, N.M.) and artificially dried without affecting flavor.

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Esteban A. Herrera

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Esteban A. Herrera and Jesus Arreola

This study was performed during 1995, 1996, and 1997 seasons in a mature pecan orchard thinned 25% in 1993, 1994, or 1995. In the orchard section thinned in 1994, more trees were removed in 1995 to reach 50% thinning. Shoot length in eight sides of the canopy periphery was measured in each growing season. Shoot growth was increased in thinned orchard sections compared with the unthinned orchard areas. Shoot growth during 1995 and 1996 was higher for trees sections thinned 25% in 1993 and 1994. Regardless of thinning years, shoot length was lower in the north side than in other canopy sides. A trend for nut yield increment was observed in thinned orchard blocks, especially where 50% tree removal was performed. Nut quality expressed in kernel percent was more related with crop load than to thinning percent or thinning year.

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Esteban A. Herrera and Jesus Arreola

This study was conducted during 1996 and 1997 in a mature pecan orchard gradually thinned over 3 years. Twenty-five percent of the trees were first removed in 1993, 1994, or 1995. The orchard thinned in 1994 was further thinned to 50% in 1995. Diffuse photon flux density of photosynthetic active radiation (PAR) was measured within the tree canopy before and after tree thinning. Sunlight penetration measurements were taken on eight tree sides as follows (N, S, E, W, NE, SE, NW, NE), 24 readings were taken on each tree side three times a day. As expected, penetration of PAR inside the tree canopy increased as thinning reduced tree density. PAR levels recorded at 9, 12 or 15 daytime hours within the tree canopy increased as the solar time increased. Lower light values were found in the north side of the tree canopy compared to other tree sections.

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Rebecca A. Kraimer, William C. Lindemann and Esteban A. Herrera

From March through June 1996, 15N-labeled fertilizer was applied to mature pecan trees [Carya illinoinensis (Wangehn.) K. Koch] in a commercial orchard to determine the fate of fertilizer-N in the tree and in the soil directly surrounding the tree. The concentrations of 15N and total N were determined within various tissue components and within the soil profile to a depth of 270 cm. By Nov. 1996, elevated levels of 15N were greatest at depths just above the water table (280 cm), suggesting a substantial loss of fertilizer-N to leaching. Recoveries of 15N from tissue and soil at the end of 1996 were 19.5% and 35.4%, respectively. Harvest removed 4.0% of the fertilizer-N applied, while 6.5% was recycled with leaf and shuck drop. In 1997, with no additional application of labeled fertilizer, the tissue components continued to exhibit 15N enrichment. By the end of the 1997 growing season, 15N levels decreased throughout the soil profile, with the most pronounced reduction at depths immediately above the water table. Estimated recoveries of 15N from pecan tissue (excluding root) and soil at the end of 1997 were 8.4% and 12.5%, respectively. In 1996 and 1997, 15N determinations indicated an accumulation of fertilizer-N in the tissues and a loss of fertilizer-N to the groundwater. Early spring growth, flowering, and embryo development used fertilizer-N applied the previous year, as well as that applied during the current year.

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Rebecca A. Kraimer, William C. Lindemann and Esteban A. Herrera

The recovery of late-season (September) 15N-labeled fertilizer (N at 55 kg·ha-1) was followed in mature pecan trees [Carya illinoinensis (Wangehn.) K. Koch] and soil (0-270 cm) from 1996 (application year) through 2001 (end of study). Recovery of late-season applied 15N was compared to the recovery of six 15N applications (March through June, N at 221 kg·ha-1) of a previously reported study. By Nov. 1996, both fertilizer schedules exhibited considerable 15N accumulation below the rooting zone and just above the water table (280 cm), with 43.4% and 35.3% 15N recovered from the soil sampling profile of the September and March-June schedules, respectively. 15Nitrogen recoveries from perennial storage tissues (root and wood) were 20.6% and 10.1% under the September and March-June schedules, respectively. The 15N recoveries from annual abscission tissues (leaf, shuck, and nut) were 1.4% and 10.6% under the September and March-June schedules, respectively. By the end of the 2001 growing season, 4% and 9% of the 15N remained in the soil following the September and March-June applications, respectively. Under both fertilizer schedules, >80% of the fertilizer-N was lost to the environment through natural processes and very little was removed during harvest. Nearly 6 years following application, perennial storage of 15N remained greater in the September application (4.3% of the 15N applied) than in the March-June application (2.7% of the 15N applied). Late-season application of fertilizer-N during the kernel filling stage was stored in perennial tissues for use the following year; very little was used for current year growth of annual tissues. Increased accumulation of perennial storage N by late-season application may reduce the depletion of N caused during a heavy-cropping on-year and may moderate the alternate-bearing trend in pecan by providing a greater reservoir of N the following year.

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Juan L. Silva, Frank B. Matta and Esteban A. Herrera

Pecans [Carya illinoinensis (Wangenh. C.) Koch] were harvested weekly for 9 and 7 weeks until normal harvest time during 1986 and 1987, respectively. Kernels were tested for chemical, physical, and sensory properties. Moisture decreased from 13% at initial harvest time to 4% to 6% by normal harvest. Free fatty acids decreased from 0.5% to 0.2% by the third week before normal harvest. Tannins fluctuated, but averaged about 0.8%. Hue angle remained constant from the fourth week to normal harvest. Shear force increased from 90 to 135 N by the second week before normal harvest. Pecans can be harvested about 2 weeks before normal harvest without significant quality deficiencies.

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Juan L. Silva, Estuardo Marroquin, Frank B. Matta and Esteban A. Herrera

This work is the result of 3 years of collaborative research between Mississippi State Univ. and New Mexico State Univ. Physical, chemical, and sensory characteristics were studied to assess eating quality of popular New Mexico pecan (Carya illinoinensis) cultivars. The force and energy necessary to break (shear) pecan nuts, and Hunter `a' and hue angle values varied with harvest year and cultivar. All other traits, including sensory evaluation results, varied only with cultivar. `Ideal' was of light color, small size, and not as firm as the others, while `Burkett' was soft and slightly rancid. `Wichita' was the cultivar rated best by panelists, despite its slightly darker color. `Western Schley' and `Salopek' were also acceptable, although not as acceptable as `Wichita'.