Nitrogen uptake and allocation by field‐grown ‘Arapaho’ Thornless blackberry

Abstract

Spring surface applications of ¹⁵nitrogen (N)‐labeled urea were made in March 1995 and 1996 on one and two‐year‐old, field‐grown ‘Arapaho’ blackberry (Rubus subgenus Rubus) plants. Individual whole‐plant samples were collected 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 were also taken from within the plant drip line at each sample date. Plant tissues were washed, dry weights measured, ground for acid digestion, total N determined, and ¹⁵N 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 while roots and primocane leaves contained more in October of each year. Floricanes 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 percent recovery of fertilizer N from topsoil among sample dates. Recovery of fertilizer N from subsoil in the October sample was much lower than that in May, probably due most to plant uptake, but also possibly to a downward movement out of the sample area by leaching or from other loss mechanisms. Averaging 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 volatilization, leaching, and/or denitrification.