Apple Tree Rootstock and Fertilizer Application Timing Affect Nitrogen Uptake

15 N, N cycling, nutrient uptake Abstract. 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% 15 N. 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. summer or fall. Mature almond trees (Prunus amygdalus L.) grown in sandy soil showed an inverse relationship between date of applica- tion and leaf tissue enrichment from labeled fertilizer applied the previous season (Weinbaum et al., 1984). Young apple (Malus × domestica Borkh) trees grown in pots also showed a clear seasonal effect for nitrate up- take, with the highest recovery observed for the August application (60%), followed by March (40%), and the lowest recovery after October application (16%) (Hill-Cottingham and Lloyd-Jones, 1975). In a recent publication using mature apple trees to study N timing and partitioning, Khemira et al. (1998) showed that spring N treatment partitioned to fruit, leaves, and shoots, while late summer application favored roots. However, preharvest application of 15 N showed highest recoveries in leaf and shoots the year after application and showed higher utilization efficiency than spring treatments. New size controlling apple rootstocks have been introduced during the last several years. However, detailed comparisons of N uptake ability of these apple rootstocks remain unre- ported. The objective of this research was to evaluate differences in N recovery between ten different apple rootstocks and to determine the effect of application timing on N uptake and recovery.