The Perfect Match: Adjusting High Tree Density to Rootstock Vigor for Improving Cropping and Land Use Efficiency of Sweet Orange

The rise in the productivity of sweet orange in Brazil has been related to the use of superior
rootstocks and higher tree density, among other factors. In order to investigate whether the cropping
system and the land use efficiency would benefit from more intensive cultivation, the performance of
Valencia sweet orange was evaluated over nine years on four rootstocks, which induced contrasting
vigor, at 513, 696 and 1000 treesha􀀀1. Agronomic Institute of Campinas (IAC) 1697 and IAC
1710 citrandarins, and diploid and allotetraploid (4) Swingle citrumelos were classified as semidwarfing,
super-standard, standard, and dwarfing rootstocks, respectively. The fruit yield per
tree was decreased at higher tree densities, notably for more vigorous rootstocks. Conversely,
the cumulative productivity was increased over the evaluation period by 27% at 1000 treesha􀀀1,
irrespective of the rootstock, and the most vigorous rootstock resulted in 2.5 times higher production
than the dwarfing one on average. Most fruit quality parameters were seldom influenced by the
tree density, while the rootstock was a decisive factor in improving the quality and the soluble
solids content. Dwarfing rootstocks allowed for harvesting 17% more fruit per minute by manual
pickers. Because the tree row volume per area is lower with such rootstocks, even at higher tree
density, spray volume can be reduced, although appropriate equipment should be developed for
better spray coverage on smaller trees. Nine years after planting under strict vector control, the
cumulative incidence of huanglongbing-symptomatic trees on IAC 1710 was double that on Swingle
4. Taken together, the results suggested that the land use efficiency in the citrus industry can be
further improved by planting vigorous rootstocks at moderate to high tree densities. Nevertheless,
obtaining highly productive semi-dwarfing and dwarfing rootstocks is the sine qua non for making
high-density pedestrian sweet orange orchards more profitable