Nitrogen uptake and allocation by field-grown 'Arapaho' thornless blackberry

Spring surface applications of (15)nitrogen (N)-labeled urea were made in M arch 1995 and 1996 on one and two-year-old, field-grown 'Arapaho' blackberr y (Rubus subgenus Rubus) plants. Individual whole-plant samples were collec ted at pre-harvest (late May), post-harvest (mid-July), and early dormancy (late October). Plant parts separated for analysis were roots, primocanes, floricanes, primocane leaves, floricane leaves, and fruits. Soil samples we re also taken from within the plant drip line at each sample date. Plant ti ssues were washed, dry weights measured, ground for acid digestion, total N determined, and N-15 analyzed. Plants collected in October had more total dry matter, with roots, primocanes, and primocane leaves contributing most to this total. Total N content decreased in all vegetative tissues (leaves and canes) from May to October. Compared to other plant tissues, floricane leaves and primocanes recovered significantly more fertilizer N in May whil e roots and primocane leaves contained more in October of each year. Floric anes and fruits did not increase in fertilizer N levels during the sampling period Overall, the lowest percent fertilizer N recovery for whole plants was 12.8% for May 1995 and the highest was 32.4% for October 1996. Recovery of fertilizer N in the topsoil ranged from a low of 12.9% in October 1995 to a high of 38.6% in May 1996. There were no statistical differences in pe rcent recovery of fertilizer N from topsoil among sample dates. Recovery of fertilizer N from subsoil in the October sample was much lower than that i n May, probably due most to plant uptake, but also possibly to a downward m ovement out of the sample area by leaching or from other loss mechanisms. A veraging all sample dates, recovery was 59.5% in 1995 and 75.8% in 1996 for the plant and soil combined, with the remainder probably lost via volatili zation, leaching, and/or denitrification.