Abstract

Spurs serve as the fundamental bearing units in almond. Mature almond trees bear a high percentage of fruit on these short shoots, with only a small percentage (fewer than 15%) of fruit born laterally on long 1-year-old shoots (Heerema et al., 2008). As a result, maintenance of the total number of living spurs per tree and ensuring their productivity is extremely important. This study evaluated the effect of fruit presence in leaf nitrogen (N) content and the effect of foliar sprays and different N treatments on spur leaf area. One hundred forty four commercial almond trees receiving differential rates of N for three prior years (140, 224, 392 kg/ha) were selected. In each tree 33 spurs were selected (a total of 4,752) and divided in three different categories [non-fruiting spurs (NF); one-fruiting spurs (F1); two-fruiting spurs (F2)]. Differential soil N and foliar nutrients were then applied and the effects on leaf nutrient concentrations and spur leaf area were determined. Leaf N concentrations declined as season progressed and were negatively correlated with whole tree nutrient accumulation in fruit. Leaf N concentration was significantly decreased by the number of fruits on the spur and there was a marked reduction in spur leaf area. Soil N and multi element foliar applications significantly increased spur leaf area however these effects did not fully compensate for the reduction due to fruit presence. Results suggest that spurs act as semi-autonomous units on the almond tree and that soil N application can reduce fruit induced loss of spur leaf area. Foliar applications only enhanced leaf area when applied to low N trees.