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Nitrogen at 112 and 224 kg·ha-1 and K at 0, 56, 112, 168, and 224 kg·ha-1 were applied to young `Desirable' pecan [Carya illinoensis (Wangenh.) C. Koch] trees to evaluate their influence on leaf scorch. Scorch severity in the orchard decreased with time even though large imbalances of N and K existed. Scorch was increased only slightly by the high N and the zero K treatments. Little scorch was observed in trees receiving K applications. Increasing K rates >56 kg·ha-1 did not reduce scorch. Correlation was not significant or very weak for leaf N, leaf K, or the leaf N: K ratio with leaf scorch in the Ray City, Ga. study, depending on the year of observation. Another study at Tifton, Ga., revealed no correlation between scorch and leaf K or the leaf N: K ratio. A very weak correlation occurred for scorch and leaf N in 1 of 2 years.
NAA was applied to pecan nuts at concentrations of 0, 20, 50, 100, 200, and 500 μg·g-1 on May 19, June 16, and July 20. The 500 μg·g-1 concentration induced nut drop at all dates but was phytotoxic to leaves when applied on May 19. Concentrations of 50-100 μg·g reduced preharvest drop of nuts.
Potassium was applied to old `Stuart' pecan [Carya illinoensis (Wagenh.) C. Koch] trees only when leaf concentrations dropped below thresholds of 0.25, 0.50, 0.75, or 1.00% K or annually, regardless of leaf K. Depletion of K was extremely slow, with soil K concentrations remaining at 68 to 168 kg·ha-1 (medium) or higher in the 0 to 15 and 15 to 30 cm depths after 20 years without K application. No trees were below the 0.25% leaf K threshold over the 20-year period. Yield, tree growth, nut quality, and tree appearance were similar for all K treatments. A leaf K threshold of 0.75% seemed adequate and practical for the low end of the sufficiency range.
Nitrogen was applied at 112 kg·ha-1 to mature 'Stuart' pecan (Carya illinoinensis (Wangenh.) C. Koch] trees, but the radii of the application were limited to 4.6, 6.1, 7.6, or 9.1 m. Yield, nut size, percentage of kernel, tree growth, and appearance were not affected by concentrating the N application. Leaf N was highest for the largest N application radius, but all treatments supplied abundant N. Concentrating N reduced soil pH and occasionally P, K, and Ca in the 0–15 or 15–30 cm soil layers, but all three soil nutrients and Mg were medium to high after 19 years of treatments.
Soil amendments of complete fertilizer, manure and limestone added to backfill soil at transplanting did not influence pecan tree appearance or growth. Removal of ⅓ or ½ of the top at transplanting was compared with no top removal. Removal of ½ the top improved tree vigor the first year but differences in vigor and growth had dissipated by the second year. With 60 cm diameter holes, vigor and growth increased as depth increased from 30 to 90 cm. Trees planted in a 20 cm diameter post hole had poorer vigor and growth the first two years than trees planted in 60 cm diameter × 90 cm depth hole. Differences in vigor and growth due to hole size also dissipated with time and were not significant at the end of the third year. Pecan trees apparently are resilient and can overcome a poor transplanting job.
A threshold of 2.75% N was most practical for the low end of the sufficiency range when lower thresholds of 2.25%, 2.50%, 2.75%, and 3.00% were tested on old `Stuart' pecan [Carya illinoensis (Wangenh.) C. Koch] trees. Application of 224 kg N/ha annually reduced nut size when compared with application of 112 kg/ha made only when leaf N dropped below 2.25%, 2.50%, 2.75%, or 3.00%. Yield and tree growth were similar when 112 kg·ha-1 was applied only when leaf N dropped below 2.75% and when 224 kg·ha-1 was applied annually. No N application was necessary to meet the 2.75% threshold for 3 of the 16 years.