The uptake efficiency of apple scions and rootstocks has not been studied in the field. Using 15N (ammonium nitrate, 1 atom % 15N) we compared nitrogen uptake efficiency of 12 rootstocks grafted to one scion (Gala) and of 20 scions on the same clonal rootstock (M.9 EMLA) in orchards located in northeastern Wisconsin. Trees were treated in either Fall or Spring 1998 with 40 g actual N per tree applied as a liquid to the soil. N uptake was assessed by measuring 15N in leaf and wood tissue taken monthly from June to Oct. 1998. Tissues were oven-dried and analized using a ratio mass spectrometer. Treatment differences were greater among scions with the same rootstocks than among rootstocks with the same scion. Total N and 15N content differences were found between roostocks and these values were inversely related to tree size.
Nitrogen (N) uptake was compared on 10 dwarf apple rootstocks (M.9 EMLA, M.26 EMLA, M.27 EMLA, M.9 RN29, Pajam 1, Pajam 2, B.9, Mark, B.469, and M.9 T337) grafted with the same scion (`Gala') in a four year-old orchard. Trees were treated in either Spring or Fall 1998 with 40 g of soil applied actual N per tree using ammonium nitrate enriched to 1% 15N. Both percentage of N (%N) and N from fertilizer (NFF) in leaf tissue were highly affected by the rootstock and the season of N application. Generally, higher %N and NFF were observed for spring than fall applications, except for leaves collected during early June 1998. Generally, M.26 EMLA, M.27 EMLA, and M.9 RN29 were the most efficient rootstocks in N uptake for spring applied nitrogen. M.9 EMLA was most efficient late in the season following fall application. Mark was more efficient early in the season for fall applied N than spring application. However, trees on Mark rootstock had the lowest %N throughout the season regardless of the time of N application. Pajam 1 and Pajam 2 were the least efficient rootstocks in N uptake following fall N application. Rootstock also significantly affected %N and NFF of wood tissue. Generally, trees on B.469 had the highest %N in their wood regardless of the season of application. No single rootstock had consistently higher N from fertilizer in their wood tissue after spring application. At the May 1999 sampling date, M.26 EMLA had higher NFF than M.27 EMLA, Pajam 1, Pajam 2, and B.9 with a fall application. Other rootstocks were intermediate. Samples collected in August showed that Pajam 1 was the least efficient rootstock in N uptake for fall applied N compared to other rootstocks, except for Pajam 2 and B.9 that were intermediate. Leaf and wood tissue analysis showed that different rootstocks had different N uptake efficiencies throughout the season. Generally, M.26 EMLA, M.27 EMLA, M.9 RN29 and M.9 EMLA were more efficient at N uptake regardless the season of N application. Pajam 1 and Pajam 2 were the least efficient.