Site-specific growth and nutrition of planted Piceamariana in the Ontario Clay Belt.: II. Effects of nitrogen fertilization

Abstract

Bioassay and field outplanting experiments in three black spruce dominated ecosystems examined 1st- and 2nd-year responses of Piceamariana (Mill.) B.S.P. seedlings to nitrogen fertilization in the same season as outplanting. The two experiments also tested a previous diagnosis of relative N deficiency on lowland Alnus–Herb poor and Ledum sites compared with an upland Feathermoss site, and allowed comparison of responses to N addition under operational and more controlled conditions. In the bioassay, fertilizer growth response was greatest and comparable on the two lowland sites, confirming the N deficiency. In the field experiment, results from these two sites demonstrated significant seedling response to N only on the Ledum site, while competing vegetation appeared to limit growth increase on the Alnus site. A comparison of bioassay and field results demonstrated a lag in shoot fertilizer response in the field, and a lesser response on the Alnus site indicated the necessity of testing cultural manipulations under operational conditions. However, the pot trial was useful in that it confirmed the initial diagnosis made by site comparison. Interaction of site factors with the N treatment emphasized the importance of calibrating fertilizer response within a framework such as the Clay Belt Forest Ecosystem Classification system.