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  • Author or Editor: Humberto Núñez x
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Pecan has an irregular bud break under mild climate areas, difficulting pollination and reducing yields, particularly in seasons when chilling accumulation is low and when only 50% of buds open. Hydrogen cyanamide (H2C N2) at 1, 2, 4% alone or with mineral oil (MO) at 2, 4% were evaluated for their effect on lateral bud opening of `Wichita' pecans, spraying branches on january 25 or february 8. H2C N2 and its mixtures with MO advances bud break 25 and 18 days as compared to control on first and second date application respectively; by march 20th shoots on applied branches had 8-14 cm lenght while control and MO treatments had only 2-3 cm.

Initial bud break was up to 85% on treated branches as compared to 60% of control; however and regularly, some shoots emerging from buds abscise thereafter. Remaining shoot number per branch was 4.8 with 4% H2C N2 or the mixture 2% H2C N2 + 2% MO on the first application date, and with 4% H2C N2 + 2% MO on the second date, as compared to 2.5 shoots of control. A 12% bud injury occurred with 4% H2C N2 on first date application and high rates of mo of second date.

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The effect of cattle manure or combined manure and zinc (Zn) application on Zn uptake, mineral composition, and yield and nut quality in pecan trees [Carya illinoinensis (Wangenh.) C. Koch] was evaluated. In 2006, treatments evaluated were: manure (12 ton/ha; M), manure plus Zn (12 ton/ha plus 129 kg Zn/ha as ZnSO4; MZ), and an untreated control. During 2007, two more treatments were added with doubled manure and Zn rates. New treatments were manure 2× (24 ton/ha; M2) and manure 2× plus Zn 2× (24 ton/ha plus 258 kg Zn as ZnSO4; M2Z2). Manure was broadcast on the soil in a 2.5-m wide band 2 m from the trunk. Zinc sulfate was broadcast over the manure, and then manure and Zn were disked into the top 10 cm of soil. In 2008, in five of nine sampling dates, significant treatment effects were detected on leaf Zn concentrations. On all of the dates, M2Z2 had the highest foliar Zn levels. During the Summer 2008 (17 July) foliar Zn in M2Z2, treatment reached 66 μg·g−1; the control treatment level was 45 μg·g−1. Nut yields were higher in treatments receiving manure, with or without Zn in the first year, and highest in the untreated control the second year. No differences were observed in trunk growth, leaf area, leaf weight, or nut growth. Kernel percentages were over 61.4 in the 3 years of study in all treatments. Largest differences among treatments in nut size were found in 2007; nut weight in the control treatment was 7.5 g per nut and in M was 8.0 g per nut. Nut weight was smaller during 2008 when nut yield was high, and the untreated control nuts were smaller than those from treated trees. The manure and manure plus Zn treatments increased foliar Zn levels in pecan trees after 3 years of annual applications. In 2008, significant differences in leaflet Zn concentration among treatments were detected with M2Z2 having the highest concentrations.

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The effect of soil banding zinc sulfate and zinc (Zn)-EDTA was evaluated over a period of 4 years on established ‘Wichita’ pecans [Carya illinoinensis (Wangenh.) K. Koch] growing in alkaline, calcareous soil. Treatments evaluated were ZnSO4 applied at 74 kg Zn/ha and Zn-EDTA at 19 kg Zn/ha. These materials were applied just once on 23 Mar. 2005. Fertilizers were injected in two bands placed 1.2 m from either side of the trunk of the tree and 18 cm deep. Treatments were replicated four times in a randomized complete block design. Data collected included foliar Zn concentrations throughout the season, midseason foliar nutrient concentrations, leaflet growth, nut yield, and nut quality. Significant differences in foliar Zn levels were found 1 month after application of Zn-EDTA. Differences also were noted during the next 3 years on ≈25% of the sampling dates. Yields of in-shell pecans averaged 2800 kg·ha−1 during the 3 years of harvest but were unaffected by treatments. Nut quality also was unaffected. Nut kernel percentage was very high, ranging from 61.2% to 63.6% during the study. Growth, measured as leaflet area and trunk cross-sectional area, was unaffected by Zn application. Chlorophyll index ranged from 47.5 to 48.0 in 2007 and from 44.7 to 45.4 in 2008 and was unaffected by applied treatments. Zn-EDTA increased Zn uptake slightly by ‘Wichita’ pecan trees in alkaline, calcareous conditions during 3 years after one soil band injection. Ongoing research on potted pecan trees (with the same soil used in the present study) suggests that Zn-EDTA can very effectively increase Zn uptake if placed in close proximity to the tree roots. Additional research is needed to refine application and placement methods in these types of soils to produce a more effective and consistent response.

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Measurement of nutrients in leaf tissue is a practical method of monitoring the nutritional status of perennial crops such as pecan (Carya illinoinensis, Wang. C. Koch). Accurate interpretations require known standard concentrations for the crop and region. To determine standard concentrations for pecans, focusing on those grown in the desert southwest, we conducted a survey of 135 `Western Schley' pecan trees in Arizona for 2 years. Leaf nutrient concentrations and yield were collected for each tree. Leaf nutrient concentrations from the highest yielding trees (50th yield percentile) were used to calculate a mean and CV for each nutrient. Results were compared with data from New Mexico, Georgia, and Sonora, Mexico. Relatively large differences were noted in mean K, Ca, B, Cu, Fe, Mn, and Zn levels. Nutrient interpretation ranges were calculated based on Arizona population statistics using the balance index method.

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