Vol. 84 No: 3

Title:
Is nitrogen stress more apparent in shaded, fruiting almond spurs than in exposed, non-fruiting spurs?

Authors:
R.J. HEEREMA, S.A. WEINBAUM, B.D. LAMPINEN and T.M. DEJONG

pp: 355-359

Abstract:
Leaf abscission rates and nitrogen concentrations in persistent leaves were tracked on non-fruiting and fruiting almond [Prunus dulcis (Mill.) D.A.Webb] spurs located in either well-exposed or shaded canopy positions. Fruiting spurs, especially in shaded positions, had higher mid-season leaf abscission rates than did non-fruiting spurs, and the difference in abscission rates between shaded, fruiting spurs and other spur sub-populations increased with tree nitrogen deficiency. Nitrogen concentrations and contents of persistent leaves were lower on fruiting spurs than on non-fruiting spurs. Nitrogen contents of persistent leaves did not decline substantially over the period of kernel development (a period of high nitrogen demand by the fruit) regardless of spur shading and fruiting status, or tree nitrogen status. This indicates that little net nitrogen remobilisation from persistent leaves occurred during this period, even on fruiting spurs on nitrogen-deficient trees. Nitrogen deficiency accentuated nitrogen stress in shaded and fruiting spurs, as indicated by early leaf abscission. However, such differential stress was not reflected by the nitrogen concentration or content of persistent leaves during kernel development. Thus, sampling of persistent leaves from the shaded, fruiting spur sub-population for nitrogen analyses did not provide a practical, more sensitive diagnostic indicator of tree nitrogen status than did conventional leaf sampling from non-fruiting spurs.

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