Effect of Increasing Ca on NH4 Absorption and Growth of Norway Spruce (Picea abies L.) Seedlings

Abstract

ABSTRACT Nitrogen use by trees and annual plants is often low. A new technique has been suggested which uses increased soluble Ca with NH 4 to stimulate NH 4 absorption and tree growth. This study was conducted in the greenhouse using Norway spruce (Picea abies L.) seedlings. The potting mixture was a calcareous sand. The nutrient solutions were patterned after a completly balanced nutrient solution (NS). One treatment was NS alone and the other was an NS with H 2 SO 4 (NS+A, at pH 2.1). The addition of acid was designed to produce soluble Ca at 160 mg 1 -1 from the CaCO 3 present in the sand. Plant samples were taken five times at 77, 168, 231, 322 and 574 days after the initiation of the experiment. The above and below-ground growth differed significantly between the two treatments. Growth was higher in the NS+A (higher soluble Ca) than in the NS alone. Dry weight of fine roots was significantly increased at 231 days and was 60% higher at 574 days. Total tree growth at the end of the experiment increased 29% in the presence of the higher Ca (NS+A). All measured growth parameters were substantially increased - with only 2 of the 9 not significantly improved. Increasing soil solution Ca corresponded to decreased residual NH 4 concentrations (increased NH 4 absorption). The increased absorption of cations over anions produced acidity which further increased the solubility of Ca in both NS and NS+A even though the NS contained 59% NO 3 -N and only 41% NH 4 -N. The increased growth of the spruce was attributed to an increase in the solubility of Ca enhancing NH 4 absorption. Increased N absorption is known to increase vegetative growth. Significantly increased N absorption which occurred from a constant NH 4 content resulting in an increased N use efficiency with the Norway spruce at the highest soluble Ca concentration.