Determining fertilizer rate for best management practice in sandy soils to balance production requirements and environmental impacts

Proper management of nitrogen (N) fertilizer ranks as a leading issue in reducing excessive N from agro-ecosystem, considered a significant source of ground water contamination. However, determining the most effective rate of fertilizer application to balance production requirements and environmental impacts is challenging, especially in bare-root tree-nurseries on sandy soils. This study investigated N fertilizer use efficiency in two Wisconsin nurseries in an effort to develop guidelines for best-management-practices. Four levels of N fertilizer (50%, 100%, 150%, and 200% of conventional rates: 175 mgN seedling^-1 for first-year seedlings and 104 mgN seedling^-1 for second-year seedlings) were broadcasted over red oak seedlings multiple times during a growing season. Fertilizer use efficiency of red oak seedling during the growing season was 35% ± 5% regardless the seedling age. Water stress during the growing season changed N allocation; there was a two-fold increase in the root biomass N of water-stressed seedling compare to well irrigated seedlings. The relative response of seedling height, biomass, and N content to fertilizer rate indicates that conventional rates balance production requirements and environmental impacts at the southern Wisconsin nursery; although the rate can be reduced up to 50% at the northern Wisconsin nursery. Thus 88 ~ 175 mgN seedling^-1 for first-year seedlings, 52 ~ 104 mgN seedling^-1 for second-year seedlings appears to maximize production requirements while reducing environmental impacts during a growing season.