Recycling of nitrogen in field-grown ‘Cornice’ pears

Abstract

SummaryFive-year-old ‘Comice’/Trovence’ quince BA29 pear trees growing in a Central Point sandy loam soil near Medford, Oregon, were fertilized with ammonium nitrate depleted in i5N to study the capacity of the tree to use reserve N. Eight dormant trees were removed each year for three years and partitioning of biomass, total N, and depleted 15N derived from the fertilizer were evaluated for various tree components. Losses of N in harvested fruits, leaf litter, and pruning were measured. New shoots and fruits were dependent on newly absorbed N. About 45% of the reserve N was partitioned to new growth in 1989. Reserve N accounted for 48% of the N in new growth. Leaves, fruits, and one-year-old wood consumed 28% and 34% of the total N reserve pool in 1988 and 1989, respectively. The main tissues exporting reserve N were branches, trunk, and roots. Partitioning of reserve N to new tissues was affected by a heavy crop load in 1989 with more N diverted into fruits at the expense of other tree components. The data show that pear trees recycle a substantial portion of their N content. Even though new tissues obtain a portion of their N from fertilizer additions, only small amounts are required.