Effects of Nitrogen Application Rate on the Growth of Lodgepole Pine (EP 886.01e)

Introduction

Although N deficiencies are widespread in interior forests, fertilized trees may not necessarily respond positively to increased N application rate. Evidence from lodgepole pine fertilizer screening trials indicates that on some interior sites, large N applications may actually reduce growth by inducing or aggravating secondary nutrient deficiencies.

In 2000, the Ministry of Forests, Research Branch established an area-based experiment to determine the effects of N application rate on the growth and development of lodgepole pine. The site is located south of Houston, within the Dry Cool subzone of the SBS biogeoclimatic zone (SBSdk). The lodgepole pine plantation was 21 years old at the time of installation establishment.

Objectives

To determine the effects of two N application rates (200N and 400N), each applied with and without other nutrients, on the magnitude and duration of growth response in young lodgepole pine.

Treatments

The treatments include two N application rates (200N and 400N), applied alone and in combination with a "Complete Mix" fertilizer (100P, 100K, 75S, 38Mg, 3B), and an unfertilized control. Each of the five treatments is replicated three times, for a total of 15 treatment plots. Each circular, 0.07ha treatment plot consists of an inner assessment plot surrounded by a treated buffer. Growth data are collected from 50 trees within each assessment plot every 3 years. Measurements include diameter at breast height, total height, height to live crown, tree form and damage. Foliar nutrient data were obtained from all treatment plots prior to fertilization, and will also be collected after 1, 3, and 6 years.