Abstract
Relatively few published papers report the annual nutrient uptake by fruit
trees, a fact that is surprising considering that it represents the backbone of proper
fertilization in sustainable agriculture. Nutrient uptake by fruit trees can be
quantitatively assessed by following the uptake of isotopically-labeled nutrients or by
mass balances, the former being accurate but not always suitable for field studies. By
the mass balances approach, that often involves tree excavations and is less accurate
than isotopes, the amounts of nutrients taken up under field conditions can be
approximated to the amount of nutrients contained in the new biomass produced by
the tree in one year. The differential allocation of nutrients within the tree influences
the extent of nutrients withdrawn from the system (by fruit harvesting) and of
nutrient recycle (by internal recycling and through litter decomposition). Nutrient
uptake along the season differs according to the tree species and the type of nutrient
considered but, in general, trees tend to absorb nutrients faster in spring. Net uptake
of nutrients like nitrogen and phosphorus lasts longer than that of potassium, which is
remobilized in significant amounts from leaves to fruits in the last part of the season.
Data on the amount and the dynamics of nutrient uptake are already available for
many fruit trees. There is still a need to integrate this knowledge into user-friendly
site-specific systems (predictive models), to be used by field-advisors and growers.