Nitrogen induced potassium deficiency in white spruce (Piceaglauca) and Engelmann spruce (Piceaengelmannii) seedlings

Abstract

White spruce (Piceaglauca (Moench) Voss) and Engelmann spruce (Piceaengelmannii Parry ex Engelm.) seedlings grown for 2 or more years in sandy loam nursery soils in British Columbia often show yellow and necrotic shoot-tip symptoms. Chemical analysis of a white spruce and a white × Engelmann hybrid spruce provenance showed that the symptoms were associated with low needle K concentrations. After nursery growth was complete, growth tests showed that seedlings with symptoms took longer to flush and had 43% less shoot extension than normal green seedlings. To see why K fertilizer alone did not always cure the symptoms, 1.5-year-old Engelmann spruce seedlings were transplanted and grown for a further 1.5 years in a 4 × 3 × 3 factorial experiment (K level × N source × N level). Nitrogen fertilization increased growth and symptom occurrence, with sources resulting in more symptoms in the order (NH4)2SO4 < NH4NO3 < Ca(NO3)2. Potassium fertilization decreased symptoms, although not completely, but had no effect on growth. Shoot-tip NH4+ was positively correlated with symptoms, while higher levels of soil and shoot-tip K, as well as soil and shoot-tip Mg, were associated with reduction in symptoms. It was concluded that heavy N fertilization created requirements for K, and probably Mg, above the tissue concentrations normally regarded as adequate, and that K fertilization did not always eliminate symptoms because of a Mg requirement.