Effect of increasing Ca on NH5 absorption and growth of Norway spruce (Picea abies L.) seedlings

Nitrogen use by trees and annual plants is often low. A new technique has been suggested which uses increased soluble Ca with NH4 to stimulate NH4 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 completely balanced nutrient solution (NS). One treatment was NS alone and the other was an NS with H2SO4 (NS+A, at pH 2.1). The addition of acid was designed to produce soluble Ca at 160 mg 1-1 from the CaCO3 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 NH4 concentrations (increased NH4 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% NO3-N and only 41% NH4-N. The increased growth of the spruce was attributed to an increase in the solubility of Ca enhancing NH4 absorption. Increased N absorption is known to increase vegetative growth. Significantly increased N absorption which occurred from a constant NH4 content resulting in an increased N use efficiency with the Norway spruce at the highest soluble Ca concentration.