English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

Phosphorus (P) and potassium (K) deficiencies were identified in a ‘Pawnee’ pecan [Carya illinoinensis (Wangenh.) C. Koch] orchard. Deficiencies of P and K have traditionally been difficult to correct in pecan. Broadcast application of P rarely results in a positive response. Broadcast applications of K frequently require 3 or more years before a positive response was noted, particularly in soils with high clay content. A 4-year study was initiated on 10-year-old trees using soil band-applied P, K, blended P plus K, and a non-treated control. Rates were based on trunk cross-sectional area adjusted annually for tree growth. Phosphorus application alleviated leaf deficiency symptoms, increased leaf P concentration, and improved flowering. However, P application resulted in darker kernels than the control or K-treated trees. Band-applied K was not associated with observed leaf symptoms but increased leaf K above the recommended minimum level and increased the percentage of number-1 kernels. Band-applied P or blended P plus K suppressed leaf K concentrations. Blended P plus K applied as a band appeared to improve return bloom 2 of 3 years, although no improvement in leaf K concentration was noted. Pecan alternate bearing is typified by high production 1 year followed by 1 year or more of low production (Sparks, 1986). All segments of the pecan industry consider alternate bearing as the greatest factor limiting expansion (Smith and Weckler, 2010). Low crop years are normally associated with a lack of return bloom rather than flower abortion (Rohla et al., 2007). Alternate bearing trees show distinct differences in leaf K and P accumulation and depletion between large and small crops (Krezdorn, 1955; Smith, 2009). During large crop years, trees had higher concentrations of leaf K and P shortly after budbreak, perhaps resulting from greater stored reserves after a small crop (Krezdorn, 1955), or greater absorption from soil triggered by a signal from a large number of developing flowers (Smith, 2009). Shortly after the fruit begins rapid volume increase, phloem-mobile K (Marschner et al., 1996) in leaves drops and shuck K accumulates rapidly (Diver et al., 1984; Kim and Wetzstein, 2005; Pe’er and Kessler, 1984; Smith, 2009) presumably associated with carbohydrate transport (Haeder, 1977; Mengel, 1980; Mengel and Haeder, 1977; Vreugdenhil, 1985) to the developing cotyledons supporting lipid accumulation (Pe’er and Kessler, 1984). Accumulated shuck K acts to increase shuck hydration assisting in shuck opening (Pallardy, 2008; Thor and Smith, 1935). Potassium shortages have been associated with leaf margin chlorosis/necrosis and partial defoliation (Smith, 2010; Sparks, 1977), reduced kernel oil content (Hunter and Hammar, 1956), poor kernel development (Smith, 2010), greater fruit abortion (Wood et al., 2010), lower tree yield (Blackmon and Ruprecht, 1934; Smith et al., 1985), and reduced return bloom (Smith, 2010). Pecan tree yield was unresponsive to applied K in many studies (Alben and Hammar, 1963, 1964; Gammon and Sharpe, 1959; Hunter, 1956; Hunter and Hammar, 1947; Sharpe et al., 1950, 1952; Worley, 1974). However, four studies reported a yield increase with applied K (Smith et al., 1985; Wells and Wood, 2007; Wood et al., 2010; Worley, 1994). Inconsistent response to applied K was largely the result of native K availability or lack of plant uptake indicated by leaf K concentration. Frequently, multiple years of annual K application were required to elicit a response (Smith et al., 1985; Worley, 1994). Typically, applied K was more readily available in soils with a sandy texture than those with high clay content. Wood et al. (2010) demonstrated that banding K within the root zone near a drip irrigation source resulted in substantial K uptake by trees. Worley (1994) conducted a 20-year study to establish the minimum pecan leaf K concentration to achieve maximum production. He concluded that 0.75% was adequate for non-irrigated, old ‘Stuart’ trees. However, other work reported fruit drop of ‘Desirable’ could be reduced if fruit K was 1.25% during Stage II fruit drop and suggested minimum leaf K concentrations as high as 1.5% might be needed for irrigated ‘Desirable’ (Wood et al., 2010). Another study suggested that K concentrations should be adjusted based on nitrogen (N) management to yield a leaf N:K ratio of 2:1 for maximum pecan yield (Wells and Wood, 2007). Phloem-mobile P in leaves decreased rapidly as it was transported to developing cotyledons during the latter part of the growing season (Diver et al., 1984; Kim and Wetzstein, 2005; Krezdorn, 1955; Smith, 2009). Rapid P transport was later than K to developing fruit. Phosphorus accumulation was primarily in the cotyledons in the form of phospholipids used as a substrate for unsaturated fatty acid synthesis and stored as inositol hexaphosphate (Chesworth et al., 1998). The rapid accumulation of P in the fruit and concurrent depletion from the leaves resulted in leaf necrosis and partial defoliation when P was limiting (Smith, 2010; Sparks, 1977). Smith (2010) reported that leaf, kernel, and shuck P concentrations were positively correlated with weight/nut and the percentage of number-1 kernels and recommended a minimum leaf P concentration of 0.14% in July. Sparks (1988) suggested that a leaf P concentration of 0.16% may be required for pecan. However, correcting a P shortage using traditional broadcast application was frequently unsuccessful (Alben and Hammar, 1964; Hunter and Hammar, 1948, 1952, 1957; Smith et al., 1960; Worley, 1974). Sparks (1988) increased P absorption of pecan by broadcasting massive quantities of P (2.2 kg/6 m/tree P; equivalent to broadcasting 7491 lb/a P2O5). Such large amounts of P are not economically practical to correct a shortage. This study was conducted in a pecan orchard with documented shortages of P and K (Smith, 2010). The objective of this study was to correct these deficiencies using banded fertilizer applications and to determine tree response. Because broadcast applications were usually ineffective unless exceptionally large quantities of P were applied and K shortages are difficult to correct in soils with high clay content, banding the fertilizer at the edge of the vegetation-free area surrounding the tree seemed a reasonable approach. Materials and Methods The study was conducted in a10-year-old ‘Pawnee’ pecan orchard located near Cleveland, OK (36 15#43$ N lat., –96 30#3$ W long.). The Dennis silt loam soil (fine, mixed, active, thermic Aquic Argiudolls) had a pH at the start of the experiment of 4.6 at 0to 15-cm level and 4.8 at 15to 30-cm. Agricultural limestone was applied at 3.6 t·ha effective calcium carbonate equivalent. When the experiment was ended after 4 years, soil pH was 6.4 and 5.9 at 0to 15-cm and 15to 30-cm Received for publication 28 Aug. 2013. Accepted for publication 20 Sept. 2013. Approved for publication by the Oklahoma Agricultural Experiment Station. Funded by the Oklahoma Agricultural Experiment Station, Oklahoma Pecan Growers’ Association, and Cedar Creek Pecan Farms, LLC, Cleveland, OK. Regents Professor. Research technician. To whom reprint requests should be addressed; e-mail mike.smith@okstate.edu. HORTSCIENCE VOL. 48(11) NOVEMBER 2013 1411 levels. Cation exchange capacity (sum of exchangeable cations plus extractable acidity) was 11.7 meq/100 g and 9.6 meq/100 g at the 0to 15-cm and 15to 30-cm depths, respectively. Soil organic matter in the top 15 cm was 2.5%. Trees received commercial management for pests. Irrigation was provided with a subsurface drip irrigation system located 1.8 m from the trunk running the length of the row with 3.8-L·h emitters spaced 0.3 m apart. The water source for irrigation was a pond (small lake) at the lower edge of the orchard. A vegetation-free area centered on the trees was maintained 3.6 m wide and 6 m long with selected herbicides. The remainder of the orchard floor was sod that was mowed as needed. Weather records were obtained from a nearby Mesonet station operated by the Oklahoma Climatological Survey. Treatments were a control (no P or K), application of P and K alone, or a blend of P plus K. Fertilizer rates were adjusted annually based on trunk diameter measured 1.4 m above the ground. Treatments were arranged in a randomized complete block design with blocking based on trunk diameter; replicated six times using single tree plots with border trees. In 2009, rates were 4.5 g·cm crosssectional trunk area P or K, 9 g·cm crosssectional trunk area P or K in 2010 and 2011, and 4.5 g·cm cross-sectional trunk area P or K in 2012. The fertilizer sources were 46N– 0P–0K (urea), 18N–20P–0K (diammonium phosphate), 0N–0P–49.8K (potassium chloride), and a 28% N solution (mixture of urea and ammonium nitrate). Phosphorus, K, and N were applied in March each year as a band 15 cm wide and 4.5 m long, 1.8 m from the trunk on each side of the tree. Urea was added such that all trees received the same N rate, including the control. March N rates were 4 g·cm cross-sectional trunk area in 2009 and 2012 and 8 g·cm cross-sectional trunk area in 2010 and 2011. An additional 0.9 kg/ tree N from urea was hand-broadcast under the canopy in May 2009 and in 2012, 1.5 kg/ tree N (0.375 kg/tree N each application) from a N solution was injected through the drip system in four equal amounts in May and June. Trunk diameter was measured 1.4 m above the ground annually during dormancy. Leaf samples, collected annually in July, were 30 middle leaflet pairs per tree from the middle leaf on the current season’s growth. Leaves were washed using the following sequence: tap water, 0.1 N HCl, P-free detergent, and two deionized water rinses. Total washing and rinsing time was less than 1 min per sample. Washed leaves were dried in a forced-air oven at 70 C, ground to pass an 850-mm screen, and stored for later analysis. Leaf elemental concentrations of N were determined after additiona

Response of Pecan to Annual Soil Band Applications of Phosphorus and Potassium