1999. Revista Chapingo Serie Horticultura 5: 101-102.
MINERAL LOSSES OF AVOCADO TREE RESULTING FROM
ABSCISSION OF FLOWERS, FRUITLETS AND FRUITS
E.
Lahav; D. Zamet
Agricultural Research Organization, The Volcani
Center, 50250 Bet Dagan, Israel. E-mail: vhlahav@.agri.gov.il
SUMMARY
The total
nutritional loss in an avocado tree due to abscission of buds, flowers,
fruitlets and fruits is relatively small. Only 25.8 kg·ha-1 N, 3.7
kg·ha-1 P and 31.0 kg·ha-1 K are found in the abscissed
organs. Among the microelements Fe is
lost 7-50 times more than the other microelements (1.40 kg·ha-1). No
relationship was found between the nutrients and the previous or future yield
except for phosphorous. Decrease in P level in the flowers was followed by an
increase in yield the following winter. The small nutritional loss seems to be
of minor importance as a factor in avocado productivity.
Key
Words: Persea americana,
yield.
INTRODUCTION
Recording the abscission process and its intensity have shown that an
avocado tree has 0.25-1.25 million flowers (Lahav and Zamet, 1999).
Nevertheless its production is relatively low and there is no relationship
between the number of flowers and the number of fruits harvested. It may be
assumed that the large amount of organs shed are not necessarily the only
factor for low productivity. The total dry weight of the abscised matter is 15%
only of the fruits harvested. The objective of the present work was to
determine the mineral loss resulting from the massive abscission.
METHODS
During the summer of 1971 all abscised organs of 12 ‘Fuerte’ trees were
counted and weighed (Lahav and Zamet, 1999). The organs were classified to:
buds, flowers, fruitlets up to 20 mm long, fruits and other parts abscised.
These organs were washed, dried, ground and analyzed for 12 elements (N, P, K,
Ca, Mg, Na, Cl, B, Fe, Zn, Mn and Cu). Correlation coefficients were calculated
between the mineral contents and the previous (1970/1) or future (1971/2)
yields.
RESULTS
The mineral content of the various abscised organs is presented in Table
1. Among the macroelements there are relatively large losses of nitrogen and
potassium (93 and 111 g·tree-1, respectively) while iron is
the major nutrient among the microelements (5 g·tree-1).
Losses of other nutrients are small. Most of the loss is caused by the flowers
because of their relatively high proportion in the abscised organs. Nutrient
content in fruitlets and fruits is small. There is no relationship between the
nutrients and the previous or future yield except for phosphorous (Table 2).
Decrease in P level in flowers was followed by an increase in yield the
following winter (Figure 1).
DISCUSSION
The macroelements
content in the abscised organs was similar to that found in California (Cameron
et al., 1952) but the total calculated loss was generally lower. The
total loss per hectare was calculated to be only 30 kg·ha-1 of N or
K which is much less than the amount of fertilizers applied. However it should
be noted that the abscised organs are not removed from the plantation but
remain on the ground and also, nutrients are translocated back to the tree
before shedding. this translocation is possibly the cause for the negative
coefficient between P level in the flowers and yield. It should be emphasized
that P level in the leaves was never reported to be correlated with the yield
(unless an extreme deficiency exist). The relatively high amounts of iron lost
indicate its possible importance in avocado productivity.
The nutrient balance presented is incomplete since it does not include
the losses by the shedded leaves. However, it may be concluded that similarly
to the total loss in dry matter, the nutritional losses are relatively small
and of minor importance as a factor in avocado productivity.
ACKNOWLEDGMENT
We would like to thank Anat Lowengardt for her valuable help in the
preparation of this manuscript.
LITERATURE CITED
Cameron, S.H.; Muller, R.T.; Wallace, A. 1952. Nutrient
composition and seasonal losses of
avocado trees. Calif.
Avocado Soc. Yearbook 37: 201-209.
Lahav, E.; Zamet, D. 1999. Flowers, fruitlets and fruit drop in avocado trees. Revista
Chapingo Serie Horticultura 5: 95-100.
