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Michael W. Smith, Becky L. Carroll, and Becky S. Cheary

`Giles' pecan [Carya illinoinensis (Wangenh.) K. Koch] seedlings were either not mulched or mulched with wood chips arranged in a 1- or 2-m-wide square that was 30 cm deep. Mulch treatments were in factorial combination with two N rates applied as either a single application at budbreak or as a split application at budbreak and 3 weeks later. Tree height was positively related to mulch width each year of the 3-year study, and trunk diameter was positively related to mulch width during the second and third years of the experiment. Leaf P and K concentration during 2 years and leaf N during 1 year of the study were positively related to mulch width. Trees receiving the higher N rate were taller during 2 of 3 years, but leaf N concentration was not affected by N rate. No differences in the parameters measured were observed whether N was applied as a single or as a split application.

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Michael W. Smith, Becky L. Carroll, and Becky S. Cheary

`Dodd' pecan seedlings [Carya illinoinensis (Wangenh.) K. Koch] were chilled at 6C for 0 to 1800 hours in 300-hour intervals and percent budbreak and days to budbreak recorded. Chilling duration required for ≥ 50% budbreak was 900 hours. Chilling > 900 hours increased budbreak percentage and reduced time to budbreak. `Dodd' seedlings chilled at 1, 5, or 9C for 0 to 2500 hours in 500-hour intervals had more lateral budbreak after 1000 hours of chilling at SC than at 1 or 9C. When chilling hours ranged from 1500 to 2500, 1C increased budbreak of the first lateral bud compared with 5 or 9C. As chilling was increased from 1000 to 2500 hours, the days to budbreak declined, and the uniformity of budbreak increased.

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Michael W. Smith, Becky S. Cheary, and B. Scott Landgraf

A low leaf Mn concentration was detected in bearing pecan (Carya illinoinensis Wangenh. C. Koch) trees growing in an alluvial soil with an alkaline pH. Trees lacked vigor and leaves were pale in color, but there was no discernible leaf chlorosis or necrosis. Three foliar applications of MnSO4 beginning at budbreak, then twice more at 3-week intervals at rates of 0 to 3.3 kg·ha-1 of Mn increased leaf Mn concentration curvilinearly, and alleviated leaf symptoms. Results indicated that three foliar applications of MnSO4 at 2.15 kg·ha-1 of Mn plus a surfactant were adequate to correct the deficiency.

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Michael W. Smith, Margaret E. Wolf, Becky S. Cheary, and Becky L. Carroll

Two studies were conducted to determine if selected grass and dicot species had an allelopathic interaction with pecan (Carya illinoinensis Wangenh. C. Koch). Leachate from pots with established grasses or dicots was used to irrigate container-grown pecan trees. Leachates from bermudagrass [Cynodon dactylon (L.) Pers.], tall fescue (Festuca arundinacea Shreb. cv. Kentucky 31), redroot pigweed (Amaranthus retroflexus L.), and cutleaf evening primrose (Oenothera laciniata Hill) reduced leaf area and leaf dry weight about 20% compared to the controls. Bermudagrass, tall fescue, and primrose leachate decreased pecan root weight 17%, trunk weight 22%, and total tree dry weight 19% compared to the control. In a second study, trees were 10% shorter than the control when irrigated with bermudagrass or pigweed leachate.

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Laura Elisa Acuña-Maldonado, Michael W. Smith, Niels O. Maness, Becky S. Cheary, Becky L. Carroll, and Gordon V. Johnson

Nitrogen was applied to mature pecan (Carya illinoinensis Wangenh. C. Koch.) trees annually as a single application at 125 kg·ha-1 N in March or as a split application with 60% (75 kg·ha-1 N) applied in March and the remaining 40% (50 kg·ha-1 N) applied during the first week of October. Nitrogen treatment did not affect yield, and had little effect on the amount of N absorbed. Nitrogen absorption was greater between budbreak and the end of shoot expansion than at other times of the year. Substantial amounts of N were also absorbed between leaf fall and budbreak. Little N was absorbed between the end of shoot expansion and leaf fall, or tree N losses met or exceeded N absorption. Pistillate flowers and fruit accounted for a small portion of the tree's N; ≈0.6% at anthesis and 4% at harvest. The leaves contained ≈25% of the tree's N in May and ≈17% when killed by freezing temperatures in November. Leaves appeared to contribute little to the tree's stored N reserves. Roots ≥1 cm diameter were the largest site of N storage during the winter. Stored N reserves in the perennial parts of the tree averaged 13% of the tree's total N over a three year period. Current year's N absorption was inversely related to the amount of stored N, but was not related to the current or previous year's crop load.

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James A. Hardin, Michael W. Smith, Paul R. Weckler, and Becky S. Cheary

Knowledge of foliar nitrogen (N) concentration is important in pecan [Carya illinoinensis (Wang.) K. Koch] management protocols. Lower cost and/or rapid methods to determine foliar N are desirable and may result in improved management strategies as well as enable precision agricultural practices to be deployed in pecan production. This study investigates using a portable chlorophyll meter and Vis-NIR camera to rapidly determine pecan foliar N in situ. Relationships of SPAD values from a chlorophyll meter (Minolta SPAD 502Plus) and vegetative indices calculated from camera image data to foliar N determined by chemical analysis were investigated. SPAD readings were taken monthly from May through October on ‘Pawnee’, ‘Kanza’, and ‘Maramec’ pecan cultivars in Oklahoma in 2010. Images of the same ‘Pawnee’ and ‘Kanza’ trees were collected in September and October of 2010 with a truck-mounted multispectral camera using ambient light. Correlation of foliar N to SPAD values was poor in May for all cultivars but distinct significant linear relationships were found for ‘Maramec’ and ‘Pawnee’ for each of the other months tested with R 2 ranging from 0.40 to 0.87. Data from ‘Kanza’ had significant relationships in June and October with R 2 of 0.39 and 0.72, respectively. Normalized difference vegetative index (NDVI) and reflectance data extracted from Vis-NIR camera images were significantly correlated to foliar N in both months of the study on ‘Pawnee’ but only in September for ‘Kanza’. The various relationships had R 2 between 0.21 and 0.51.