Long-term Performance of Pecan Trees when Nitrogen Application is Based on Prescribed Threshold Concentrations in Leaf Tissue

Abstract

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.