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Lenny Wells

Pecan [Carya illinoinensis (Wangenh.) K. Koch] tree stem water potential (ψ), shoot length, nut yield, and nut quality for the following treatments were evaluated in a commercial pecan orchard in Berrien County, GA; 1) current recommended irrigation schedule, 2) a reduced early season irrigation schedule, and 3) non-irrigated control. Water Stress on pecan occurred at ≈−0.78 MPa using the pressure chamber to measure stem water potential. Regression analysis suggests that irrigation scheduling for mature pecan trees may be needed when volumetric water content reaches 10% on Tifton loamy sand soil. Water stress in pecan is correlated with soil moisture from budbreak through the end of nut sizing. Pecan trees bearing a moderate to heavy crop load may undergo water stress during the kernel-filling stage regardless of soil moisture level. Therefore, it is suggested that water stress during the kernel-filling period is a function of nut development, crop load, or both in addition to soil moisture. The reduced early season irrigation schedule provided a 38% reduction in irrigation water use with no significant effect on pecan tree water stress, yield, or quality, suggesting that pecan trees can tolerate moderate early season water stress with no effect on pecan yield or quality under southeastern U.S. environmental conditions.

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Lenny Wells

The prolonged period from tree planting to first commercial harvest of pecan [Carya illinoinensis (Wangenh.) K. Koch] provides incentive for many growers to intensively manage young trees to induce commercial production as soon as possible. This management includes high nitrogen (N) application rates with or without fertigation. However, there remains little data regarding the effect of N fertilization or fertigation on young pecan trees grown under southeastern U.S. orchard conditions. The objectives of this study were to compare the effects of fertigation with more commonly recommended forms of fertilization on growth and leaf N, phosphorous (P), potassium (K), and zinc (Zn) concentrations of first- through third-leaf pecan trees irrigated with microsprinklers. An optimal growth rate of young pecan trees was obtained as easily with a balanced granular fertilizer application using significantly less N compared with fertigation applications. The minimal treatment differences observed along with the fact that leaf N concentration never fell below the minimum recommended level in any treatment throughout the study supports the supposition that first-year pecan trees require no N fertilizer during the year of establishment. Only modest N application rates are required during the second and third growing seasons. This practice helps to promote optimal tree growth while minimizing excessive losses of N to the environment.

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Lenny Wells

The prolonged period from tree planting to first commercial harvest of pecan [Carya illinoinensis (Wangenh.) K. Koch] provides incentive for many growers to intensively manage young trees to induce commercial production as soon as possible. This management includes irrigation. However, there remain very few data regarding the irrigation requirements of young pecan trees grown under southeastern U.S. orchard conditions. The objectives of this study were to determine appropriate irrigation rates for young pecan trees and to compare growth of young pecan trees with drip and microsprinkler irrigation. Parameters evaluated for both experiments include trunk diameter growth, stem water potential (water stress), leaf area, leaf length, leaf width, and chlorophyll index. These results suggest that irrigation is beneficial to the growth, vigor, and alleviation of water stress on young pecan trees in the establishment phase grown in the temperate region of the southeastern United States. There was no difference in young pecan tree growth and vigor for microsprinkler irrigated trees at 304 L per week (lpw) compared with 650 lpw from the year of planting through the third leaf. Similarly, drip irrigation at 182 lpw appears to result in equal tree growth compared with both drip and microsprinkler irrigation at over 600 lpw.

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Lenny Wells

Georgia is the largest pecan (Carya illinoinensis) producing state in the United States, accounting for ≈30% of national production. Georgia’s pecan acreage has undergone at least three significant expansions since the industry’s establishment in the early 1900s. The most recent expansion was likely a result of recent price increases driven by the export market for pecans. This stimulus also led to the planting of additional pecan acreage throughout the pecan growing regions of the United States. A survey of pecan producers throughout Georgia was conducted from Jan. through Mar. 2010, 2012, 2013, and 2014 regarding the planting of pecan trees. The current survey documents the planting of 391,488 pecan trees and 15,328 additional pecan acres since 2010 in Georgia. New orchard plantings averaged 40, 35, 42, and 62 acres in size for 2010, 2012, 2013, and 2014, respectively. The state’s pecan producers planted 14 to 30 different pecan cultivars, depending on the survey year. Aside from nongrafted seedling trees planted in 2010, ‘Desirable’ and ‘Pawnee’ accounted for the highest percentage of trees planted annually until 2014, both in percentage of total trees planted and percentage of producers planting trees. The survey also indicates a shift toward the planting of pecan trees at higher density by Georgia pecan producers since 2010.

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Lenny Wells

Recent extensive pecan [Carya illinoinensis (Wangenh.) K. Koch] plantings coincided with a shift toward the planting of pecan trees at higher density by Georgia pecan producers in anticipation of maintaining these densities through hedge pruning. Initial studies of mechanical hedge pruning in the low-light environment of the southeastern United States have failed to show significant benefits to pecan production. The objectives of this study were to compare the effects of hedge pruning on pecan nut quality, yield, and midday stem water potential (ψ) of pecan trees in the temperate climate of the southeastern United States and to evaluate the effect of hedge pruning on windstorm damage to pecan trees. Treatments were arranged in a randomized complete block design with three blocks. Two treatments were evaluated; 1) Hedge-pruned; 2) Nonhedge-pruned (control). Midday stem ψ was 8.5%, 17.6%, and 16.6% higher (P ≤ 0.05), indicating less water stress, on hedged trees than on nonhedged trees during 2015, 2016, and 2017, respectively. Nut weight and percent kernel were increased (P ≤ 0.05) by hedge pruning 2 of 3 years of the study. Although no direct positive effect of hedge pruning on in-shell nut yield was observed, hedge pruning was not detrimental to pecan yield in the short term. Hurricane/Tropical Storm Irma brought damaging winds to the entire pecan-producing region of Georgia on 11 Sept. 2017, resulting in blown down trees, broken branches, and immature nuts blown from the trees. Hedged trees had 60% less wind damage in the form of major limb breakage and tree loss than did nonhedged trees.

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M. Lenny Wells

Little information is available regarding the activity of soil quality biological indicators in southeastern U.S. pecan [Carya illinoinensis (Wangenh.) K. Koch] orchards. The objectives of this study were to examine the effect of poultry litter application and the use of crimson clover (Trifolium incarnatum L.) as a cool-season cover crop on soil chemistry and soil quality biological indicators, including mycorrhizal inoculum potential (MIP), microbial biomass carbon (MBC), and phosphatase activity in a southeastern U.S. Coastal Plain pecan orchard system. The use of clover as a cool-season cover crop between tree rows provided multiple benefits for pecan orchard soil quality, including increased MIP and MBC. Soil phosphatase activity was also enhanced by clover during two of the three years of study. Soil elemental properties, including total nitrogen (N), and soil organic matter (SOM) were also enhanced by clover and/or poultry litter, although there was an obvious time lag in the response of soil N to the treatments. Poultry litter application increased soil phosphorus (P) but did not consistently enhance soil biological activity parameters. At times, poultry litter appeared to neutralize or minimize the positive effects of clover on MIP.

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M. Lenny Wells

Application method and placement can improve the efficiency of applied nitrogen (N) per unit of yield, potentially minimizing N loss and increasing the profit margin for pecan producers. The following treatments were evaluated for their effect on pecan leaf N concentration, pecan yield, nut quality, agronomic N use efficiency (AEN), and alternate bearing intensity (I); 1) emitter-adjacent application of liquid urea ammonium nitrate (UAN) (28N–0P–0K) with 5% sulfur (S); 2) broadcast application of dry ammonium nitrate (34N–0P–0K); 3) broadcast-band application of dry ammonium nitrate; 4) broadcast ground-spray application of liquid UAN; and 5) untreated control (2009–12). Leaf elemental tissue analysis, pecan yield, quality, and alternate bearing intensity indicate that pecans can be effectively fertilized with N using any of the application methods used in the current study. Based on AEN, it appears that pecans can be effectively fertilized at a lower field rate of N than is currently recommended and that the volume of fertilizer applied to pecan orchards can be significantly reduced by minimizing the area in the orchard to which N fertilizer is applied and eliminating excessive applications to vegetated row middles, which apparently offer little additional benefit to pecan leaf N, pecan quality, or yield.

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M. Lenny Wells

Nitrogen (N) fertilizer application to plants at rates not adjusted for the N contribution from soil N availability may result in overapplication of fertilizer. Further understanding of proper timing of N applications based on soil N dynamics and plant demand can be valuable information for the efficient use of fertilizer N. The present study measures soil N dynamics in a pecan orchard under various N fertilizer regimes on a southeastern U.S. Coastal Plain soil. The following treatments were evaluated: 1) crimson clover (Trifolium incarnatum L.); 2) poultry litter; 3) crimson clover + poultry litter; 4) ammonium nitrate (NH4NO3); and 5) untreated control. Crimson clover provided from 20 to 75 kg·ha−1 N over the course of the two growing seasons; however, most of the available N from crimson clover became available late in the growing season. As a result, supplemental N may be required in spring where crimson clover is used as an orchard cover crop. Poultry litter, with and without clover, provided available N consistently throughout the growing season with more N becoming available later in the season than earlier. This suggests that poultry litter applications for pecan should be timed before budbreak. Under optimum environmental conditions, N from NH4NO3 is most available within the first 30 days of application. Thus, it appears that synthetic fertilizer applications using NH4NO3 as the N source should be targeted at or 2 to 3 weeks after pecan budbreak.

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M. Lenny Wells

This study was established to assess the effects of a severe late spring freeze on flowering, shoot growth, leaf nutrient status, and the retention of fruit developing from secondary buds of pecan [Carya illinoinensis (Wangenh.) K.Koch]. Freeze damage appears to have a significant influence on pecan physiology and fruit retention. ‘Desirable’ produced a crop of pistillate flowers from secondary buds after the freeze; however, many of these flowers were abnormal in appearance. Freeze-damaged ‘Desirable’ trees exhibited shorter shoots, reduced flower and fruit retention, a lower chlorophyll index, and decreased leaf nitrogen concentration compared with nondamaged trees. Leaf zinc concentration was higher in freeze-injured ‘Desirable’ trees than in nondamaged trees. Freeze-damaged ‘Kiowa’ trees had longer shoots and failed to produce a crop of pistillate flowers from secondary buds on most shoots. Freeze damage led to the appearance of mouse-ear leaf symptoms and reduced leaf chlorophyll index, leaf nitrogen, and leaf magnesium concentrations in ‘Kiowa’. Leaf phosphorous and leaf potassium concentrations were higher in freeze-injured ‘Kiowa’ trees than in nondamaged trees. These observations provide insight into the potential response of bearing orchard trees injured by a late spring freeze.

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M. Lenny Wells

This survey addresses the current nutritional status of orchards typical of a large portion of the United States pecan (Carya illinoinensis) industry. A leaf nutrition and soil fertility survey was conducted for commercial orchards in a major production area of the U.S. pecan belt, which is located in southern Georgia. The study sampled pecan orchards from 18 July to 5 Aug. 2005 and 17 July to 3 Aug. 2008. All orchards had a history of commercial level orchard management, and represented a wide range of orchards typical of the region. Results indicate that southeastern U.S. pecan producers should focus their nutrient inputs on nitrogen (N), potassium (K), sulfur (S), and copper (Cu) as needed. The survey results show that leaf N can vary widely by season and among orchard locations. Evidence indicates that many growers could likely forego the soil application of phosphorous (P) and zinc (Zn) until leaf or soil analysis indicates a need. Orchard soil organic matter (SOM) in 2008 averaged 3.63%, and ranged from 1.74% on coarse-textured sandy soils to 5% on sandy loam soils. Both SOM and soil nitrate-N were higher in orchards using clover (Trifolium spp.) as a cool-season orchard groundcover than those using a grass sod only. The mean carbon:S ratio of Georgia pecan orchard soils was 504:1, which may further reduce tree uptake of S from low-S soils.