Vegetative Growth and Nitrogen/Carbon Partitioning in Blueberry as Influenced by Nitrogen Fertilization

Nitrogen uptake and N and C partitioning were evaluated in `Sharpblue' southern highbush blueberries fertilized with different N forms. Plants were grown in acid-washed silica sand and fertilized with a modified Hoagland's solution supplemented with 5.0 m m N as NH 4 + or NO 3 - . Nutrient solution pH was adjusted to 3.0 and 6.5 for the NO 3 - and NH 4 + -treated plants, respectively. After 12 months of growth, plants were dual labeled with 14 CO 2 and 10% enriched 15 N-N as either NaNO 3 or (NH 4 ) 2 SO 4 and harvested 12 hours after labeling. Fertilization with NO 3 - -N increased leaf, stem, and root dry weights compared to NH 4 + fertilization. Total 15 N uptake did not differ between N fertilization treatments, thus whole plant and root 15 N concentrations were greater in NH 4 + -fertilized vs. NO 3 - -fertilized plants. Fertilization with NO 3 - -N increased C partitioning to new shoots compared to NH 4 + -fertilized plants. However, C partitioning to other plant parts was not affected by N form. Although NO 3 - uptake in blueberry appears to be restricted relative to NH 4 + uptake, this limitation does not inhibit vegetative growth. Additionally, there appears to be adequate available carbohydrate to support concurrent vegetative growth and N assimilation, regardless of N form.