The reliability of a proposed satisfactory range of 50-100 ppm Zn in the leaflet for pecan [Carya illinoensis (Wang.) K. Koch] was tested. The range was compared to: a) the average Zn concentration in the leaflets of groups of trees where a variable percentage of trees had Zn deficiency symptoms and b) to the average Zn concentration in the leaflets of trees grouped according to severity of Zn deficiency. In both situations, Zn deficiency symptoms occurred only when Zn concentration in the leaflets was less than 40 ppm.
During a 6-year study, Zn levels in pecan [Carya illinoensis (Wang.) K. Koch] leaflets from equivalent Zn rates per 50-year-old tree were greater from broadcast than from band application. Equivalent amounts of Zn per tree were applied to the soil surface on a broadcast and band basis. Broadcast rates were 0, 20, 40, 80, or 160 kg of Zn/ha. Band rates were 0, 0.4, 0.8, 1.6, or 3.2 kg of Zn/tree applied in a 15-cm-wide band. Response from broadcast was quicker than from band application in that leaflet Zn was increased above the sufficiency level with 40 kg or more Zn/ha but only by the 3.2 kg of Zn/tree in the case of the band.
Ethylene was produced by the Chinese chestnut fruit (Castanea moltissima Blume), its rate increasing substantially prior to dehiscence. The primary site of synthesis was the involucre, rather than the seeds. Elevated levels (2 to 4 μl/kg-hr) of ethylene production by the involucre corresponded with increased respiratory activity; however, the rate of ethylene synthesis declined earlier in the senescence of the involucre than did the CO2 production. Exogenous application of ethylene either as a gas or as (2-chloroethyl)phosphonic acid (ethephon) accelerated the rate at which dehiscence occurred and improved the uniformity of dehiscence among seedling fruits.
Boron was soil applied to pecan trees (Carya illinoensis (Wang) K. Koch) at the rate of 0, 12.5, 25.0, 50.0, or 100 g per tree. Boron toxicity increased with B applied. Bud break the following spring was advanced in relation to B applied and toxicity incurred.
Ground applications of ZnO to large mature pecan [Carya illinoinensis (Wangenh.) K. Koch] trees in orchards possessing an acidic soil, but with a culturally induced slightly alkaline soil surface zone, were at least as effective as was ZnSO4 for rapidly correcting severe foliar Zn deficiency, improving in-shell nut production, and maintaining kernel quality. Under such soil conditions, light disking of Zn applied at 160 kg·ha-1 from ZnO elevated foliar Zn above the sufficiency level by the second growing season after application; whereas an absence of disking delayed substantial uptake from ZnO until the fourth growing season. ZnO, usually a lower priced Zn source, was as effective as was ZnSO4 for correcting Zn deficiencies via broadcast ground application; however, same season correction of Zn deficiency was best accomplished by the standard practice of using foliar sprays of ZnSO4 rather than by heavy soil applications of either Zn source.
The range in critical physical and chemical characteristics of the shells of mature fruit (nuts) of pecan [Carya illinoensis (Wang.) K. Koch] were assessed for 16 major cultivars and 2 selections. Nut physical parameters varied widely among genotypes. Total nut weight varied from 5.3 to 10.4 g; kernel weight, from 2.8 to 5.1 g; shell weight, from 1.6 to 4.1 g; packing tissue weight, from 0.6 to 1.7 g; and shell thickness, from .62 to .98 mm. An even greater range was found among genotypes in the concentration of extractable phenolics which could be used in resins and plastics. Extractable phenolics varied from 6.3 to 20.9% of the total shell weight (shell + packing tissue), from .06 to 1.5% in the shell alone, and from 20.2 to 52.6% in packing tissue. Commercially separated samples of packing tissue contained 6.24% extractable pecan oils.
The respiratory rates of nuts of 19 pecan [Carya illinoensis (Wang) K. Koch] genotypes were determined with and without shells; at harvest moisture and at 3% kernel moisture. Shell respiration also was determined. Respiratory rates of kernels and intact nuts varied logarithmically with moisture content of the kernel. Respiratory rates of kernels at harvest ranged from 26.9 to 0.3 mg CO2kg-1hr-1; after drying to 3% moisture, values declined, ranging from 0.21 to 0.06 mg CO2kg-1hr-1. Respiration also was genotype dependent and was influenced by shell presence. The respiration rate of unshelled nuts was greater than shelled kernels when the moisture level was high, but lower when the kernel moisture level was low. Shell material was found to respire to a limited extent.