© 1997 Heron Publishing—Victoria, Canada
Leaf nutrient variation in mature carob (Ceratonia siliqua) trees in response to irrigation and fertilization
P. J. Correia (1) and M. A. Martins-Loução (2)
1. AIDA, Apartado 302, 8100 Loulé, Portugal / 2. Departamento de Biologia Vegetal, Faculdade de Ciências de Lisboa, Campo Grande, C2 Piso 4, 1700 Lisboa, Portugal / Received February 16, 1996
Summary
Seasonal variations in leaf nitrogen, phosphorus and potassium concentrations were studied in a mature carob (Ceratonia siliqua L. cv “Mulata”) orchard subjected to a 4-year irrigation and fertilization experiment. Three irrigation regimes (0, 50 and
100%), based on the evaporation values obtained from a class A pan, were tested in combination with two nitrogen (N) supply
regimes in which 21 kg ha–1 year–1 (low-N) and 63 kg ha–1 year–1 (high-N) were supplied as ammonium nitrate. Leaf nitrogen concentration increased throughout the experiment, independently
of treatments. There were no significant differences in leaf N concentration between trees in the high-N and low-N treatments.
Irrigation regimes had no effect on leaf mineral concentration but influenced the amount of leaves shed and slightly modified
the pattern of leaf shedding that occurred during the summer drought period. Nutritional balances between N and P and N and
K were both closely and significantly correlated. Potassium was translocated from leaves to fruits during spring, independently
of treatments. Severe water stress periods occurring during spring or autumn induced shedding of leaves leading to nutrient
mobilization. Nutrient retranslocation during these drought periods may represent an adaptive mechanism. Nitrogen retranslocation
was higher for trees in the high-N treatments than for trees in the low-N treatments, whereas phosphorus retranslocation was
independent of the irrigation and fertilization treatments.
Keywords:
absolute shoot growth, leaf fall, nitrogen, N/K ratio, N/P ratio, phosphorus, potassium, retranslocation.
