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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.

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M. Lenny Wells

The recent increase in the cost of synthetic fertilizer dramatically reduces the profit margin for pecan [Carya illinoinensis (Wangenh.) K. Koch] producers. The objective of this study was to investigate the effects of clover and poultry litter on the orchard soil, horticultural, and nut quality parameters of pecan in the southeastern United States. 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. Application of poultry litter with or without clover often led to higher soil phosphorous (P) and potassium (K). Poultry litter application with and without clover led to higher leaf P in the final year of study. The recurring low pecan leaf K in the presence of clover without additional K application suggests that K nutrition may be especially important in orchards where clover is used. Clover and/or clover + litter occasionally led to enhanced pecan leaf concentrations of iron (Fe), copper (Cu), and zinc (Zn). Over the course of the study, yields were more consistent from year to year in the clover, litter, and clover + litter treatments, as indicated by the low alternate bearing intensity (I) from 2008 to 2011. Leaf elemental tissue analysis, pecan yield, and quality indicate that poultry litter and clover provide adequate nitrogen (N) nutrition for pecan production.

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M. Lenny Wells

This study was established to assess the effect of aldicarb on newly transplanted pecan (Carya illinoinensis) nursery trees. Although labeled for use on pecans for more than 25 years, the aldicarb label for pecans was voluntarily dropped by the manufacturer in 2010. Bare-root seedling, ‘Cape Fear’, ‘Sumner’, and ‘Elliott’ trees were planted in Feb. 2007. Ten trees each were treated with one of the following treatments: aldicarb (0.25 lb at budbreak), aldicarb (0.25 lb applied at budbreak and again in June for a total of 0.5 lb/tree), and a nontreated control. Aldicarb increased shoot length, trunk diameter, leaf chlorophyll index, total dry weight, stem dry weight, and root dry weight of pecan seedlings after 1 year's growth. Aldicarb increased trunk diameter of ‘Cape Fear’, ‘Sumner’, and ‘Elliott’ during the course of the study. Nut production of ‘Cape Fear’ was enhanced in the third year of production. These observations indicate that aldicarb is of value in pecan orchard establishment.

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M. Lenny Wells and Bruce W. Wood

Water-stage fruit-split (WSFS) is a relatively common and often major problem of certain pecan [Carya illinoinensis (Wangenh.) K. Koch] cultivars. This study evaluates the possibility that the malady can be influenced by improving tree micronutrient nutrition. Foliar sprays of boron (B) and nickel (Ni) to WSFS-susceptible fruit of ‘Cape Fear’ and ‘Sumner’ are evaluated based on the possibility that either B or Ni potentially affects the severity of WSFS exhibited by trees. Although the incidence of WSFS on ‘Cape Fear’ was unaffected by micronutrient sprays, the severity of WSFS was substantially reduced in each of the 3 study years by foliar B application and in 2005 by foliar Ni application. Repeated foliar sprays of Ni also reduced WSFS of ‘Sumner’ fruit. These data indicate that improving either B or Ni nutrition can potentially reduce crop loss resulting from WSFS in certain orchard situations and provides evidence that insufficient availability of B or Ni to developing ovary tissues potentially predisposes developing fruit to WSFS when environmental triggers occur.

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M. Lenny Wells and Eric P. Prostko

A persistent problem was identified in pecan (Carya illinoinensis) orchards throughout southern Georgia in which pecan trees growing in rows immediately adjacent to peanut (Arachis hypogaea) fields developed hollow pecans. In-shell nut size and appearance was normal; however, the kernels failed to develop. In 2008 and 2009, research was conducted to evaluate the influence of imazapic on pecan nut development in two pecan orchards located at the University of Georgia Ponder Research Farm located near Tifton, GA. Three herbicide treatments were evaluated, including imazapic at 0.17 kg·ha−1, imazapic at 0.30 kg·ha−1, and a nontreated control. Imazapic inhibited pecan kernel production and shuck split during both years of study. In 2009, leaf potassium was reduced by the low rate of imazapic.

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M. Lenny Wells, D. Scott Carlson and R. Philip Edwards

The effects of mechanical fruit thinning on pecan [Carya illinoinensis (Wangenh.) K. Koch] yield, nut quality, and profitability were assessed using ‘Sumner’ and ‘Cape Fear’ pecan trees cultivated in a commercial orchard. The moderate to light production year (OFF year) return crop and return crop value of ‘Cape Fear’ and ‘Sumner’ was increased by mechanical thinning in the year of high production (ON year). This enhanced the 2-year total value and 2-year average value of both cultivars. Increased profitability of these cultivars with mechanical fruit thinning results primarily from higher yields and prices in the OFF year of production, which offset any loss in yield and/or crop value generated by fruit thinning in the ON year. Premature germination of ‘Cape Fear’ pecans was reduced from 34% to 4% with mechanical fruit thinning. Mechanical fruit thinning appears to be a highly valuable practice, leading to increased profit potential for ‘Cape Fear’ and ‘Sumner’ pecan.