Pruning Strategies for Young ‘Nadorcott’ Mandarin Trees Planted in High Density Orchards in South Africa

Abstract

The present study evaluated the effect of pruning according to different tree forms on yield, fruit size, and leaf starch reserves of young ‘Nadorcott’ mandarin trees planted at high density. Trees were selectively pruned by hand either according to form (pyramid or open center) by removing either lateral or central branches, or were left unpruned until trees touched each other in the row with minimal pruning thereafter (control). Form pruning, in particular the pyramid form, resulted in higher amount of biomass removal compared with the control treatment, affecting canopy volume and trunk cross-sectional area (TCSA). This led to a yield reduction in the first year, but steady yield increases in subsequent years. Fruit size was significantly larger in pyramid and open-center-shaped trees compared with the control treatment, but this difference declined as trees got older. Production efficiency (yield/canopy volume) of the pyramid form was significantly higher after the second year of pruning compared with the other treatments. Pruning did not influence leaf starch content, but indirectly affected crop load and subsequently the following year’s crop size. Judicial removal of lateral branches, e.g. in pyramid-shaped trees, appeared to be the most beneficial tree form for ‘Nadorcott’ mandarin as it is closest to its natural growth habit and promotes sustainable yields with good marketable fruit size.