Modified exponential nitrogen loading to promote morphological quality and nutrient storage of bareroot-culturedQuercus rubraandQuercus albaseedlings

Exponential nutrient loading has been used to improve nursery fertilizer uptake efficiency of conifer seedlings, but the technique has received little attention in the culture of temperate deciduous hardwoods. This study examined responses of northern red oak (Quercus rubra L.) and white oak (Q. alba L.) seedlings to modified exponential nitrogen loading during bareroot nursery culture using a broad range of nutrient supply from 0 to 3.35 g nitrogen (N) per plant per season for 18 weeks in Indiana, USA. Seedling growth and nutritional parameters followed a curvilinear pattern that ranged from deficiency to toxicity with increased fertilization consistent with trends depicted in the proposed model for nutrient loading. Fertilization increased plant dry mass by 113–260% for red oak and 49–144% for white oak. Severe nutrient deficiency occurred under indigenous soil fertility, and limited phosphorus and potassium uptake were found to inhibit seedling growth at higher N supply. The sufficiency and optimum rates were determined to be 0.84 and 1.68 g N per seedling per season, respectively, under the current cultural conditions. Fertilization at 1.68 g N per plant increased N content by 40% in red oak and 35% in white oak. This approach may be used to help refine nursery fertilization practices in hardwood culture to produce high-quality seedlings for field planting.