Nitrogen and Sulfur Interaction Influences Net Photosynthesis and Vegetative Growth of Pecan

Abstract

Seedlings of pecan [Carya illinoensis (Wangenh.) C. Koch] grown in perlite culture were treated with N and S in a 5 × 5 factorial in a randomized complete block design to determine the effect of N, S, and N × S interaction on vegetative growth and photosynthesis. Nitrogen and S deficiency symptoms occurred when leaf N and S were < 25 and 1.4 mg·g-1 dry weight, respectively. Photosynthesis was reduced when combined leaf N and S exceeded 35 and 3.7 mg·g-1 dry weight, respectively; growth was reduced when leaf N and S were > 34 and 3.7 mg·g-1 dry weight, respectively. Photosynthesis and growth increased with N supply, but depended on leaf N: S ratio. In plants without visible N or S deficiency, a N: S ratio of ≈9. is proposed to be near the optimum for maximum growth. Comparison of leaf N, S, and the N: S ratio with similar analyses in selected orchards suggests that pecan productivity will increase from S application under field conditions. We conclude that the interaction” of N and S imposes stringent controls on leaf N and S, photosynthesis, and growth.