Plant and Soil 119, 342-345 (1989).
y Kluwer Academic Publishers. Pr&ted in the Netherlands.
Effects of nitrogen fertilizers on the aluminium contents of mature tea leaf
and extractable aluminium in the soil
PHILIP O. OWUOR and DANIEL K.A. CHERUIYOT
Tea Research Foundation of Kenya, P.O. Box 820, Kericho, Kenya
Received 14 December 1988. Revised May 1989
Camellia sinensis, leaf aluminium and soil aluminium, nitrogen fertilizers, tea
Increasing rates of nitrogenous fertilizer decreased the aluminium contents in mature leaf of tea but
increased the extractable soil aluminium in the 0-30 cm soil depth. Use of NPKS 25: 5: 5: 5 or NPK 20:10:10
did not affect the order of responses. Different rates of potash had no effect on leaf aluminium levels. The
concentrations of aluminium in the mature leaf were well above the minimum required for tea nutrition. The
increase in extractable soil aluminium due to higher nitrogen rates in part explains the generally low
potassium and calcium contents in the leaf and soil.
The tea plant (Camellia sinensis) (L.) O. Kuntze
grows best on acidic soils. Such acidic soils may
normally have high levels of available aluminium.
Indeed, the tea plant has the ability to accumulate
large amounts of aluminium and more than
30,000 ppm aluminium have been recorded in the
old leaves of the tea plant (Matsumoto et al., 1976).
Large amounts have not shown any toxic effect on
the plant (Matsumoto et al., 1976), but levels below
50ppm retard growth of young teas (Ishigaki,
1984). Addition of aluminium to the soil has been
shown to accelerate growth of tea (Kinoshi et al.,
1985; Matsumoto et al.,
aluminium seems to be beneficial to proper growth.
of tea (Ishigaki 1984; Kinoshi et al., 1985) and
aluminium could be an essential nutrient for tea.
Excess aluminium improves the phosphorus uptake
(Kinoshi et al., 1985) but reduces potassium
(Ishigaki et al., 1974a) and calcium uptake by the
tea plant (Kinoshi et al., 1985).
In Kenya, the yields of tea have generally in-
creased in the last decade. This has in part been
attributed to the improved nutritional status of the
plant especially due to the use of correct rates and
types of nitrogen fertilizers (Owuor et al., 1987). In
1976). In general
the previous two papers in this series it was noted
that the improved rates of nitrogen tended to
decrease uptake of potassium (Owuor et al., 1987)
and calcium (Owuor et al., 1988) by the tea plant.
In Japan, application of ammonium nitrogen fer-
tilizer was shown to increase aluminium uptake by
the tea plant compared to nitrate nitrogen fer-
tilizers (Ishigaki, 1974b). Although aluminium is
known to interact with different nutrients which are
beneficial to the tea plant for optimum growth and
yields (Bhattachavya and Dey, 1983; Ishigaki,
1974a, b; Kinoshi et al., 1985; Sivasubramanium
and Talibudeem 1972), the effects of different rates
and sources of nitrogen on uptake of aluminium by
the tea plant and soil available aluminium are
The following studies were conducted to find out
the effects of different rates and sources of nitrogen
on aluminium availability in the soil and uptake by
the tea plant.
To the high yielding clone S15/10 at the
Kaproret Estate of the African Highlands Produce
Company, nitrogen fertilizers as NPKS 25:5:5:5
and NPK 20:10:10 were applied in a split plot
design at 0, 100, 150,
600 kg N ha- 1 year- 1. The experiment commenced
in September 1984 and leaves were sampled
towards the end of every month, except during
pruned months. Soil was sampled in December
300, 450 and
The effects of rates and ratios of nitrogen and
potassium on low yielding tea at Timbilil Estate
(Tea Research Foundation) West of the Rift Valley
are being assessed in a 4 x 4 factorial experiment
in a randomized complete block design. Nitrogen
was applied at 0, 90, 180 and 270 kg N ha -I. year-l
as sulphate of ammonia while potassium was
applied at 0, 45, 90, 135kgK2Oha-l.year -1 as
muriate of potash since September 1984. Addition-
ally all plots received 50kgP205 as double
superphosphate per hectare per year. Leaf sam-
pling was done once in the middle of every month.
The same experiment as Experiment II was done
at Karirana Estate (Limuru), East of the Rift
Valley on seedling tea. The experiment was
initiated in March 1987 and leaf sampling was done
once towards the end of every month.
Mature leaf samples were obtained and treated
as explained by Owuor et al. (1987, 1988). Soil
samples were extracted using potassium chloride
solution (Bruce and Lyons, 1984). The aluminium
contents of the samples were determined by Atomic
Absorption Spectrometry with a nitrous oxide--
acetylene flame set at 309.3nm (Puchyr and
The monthly average mature leaf contents of
aluminium of samples from different experiments
in 1987 are presented in Tables 1 and 2. Increasing
rates of nitrogen decreased the aluminium contents
of mature tea leaf linearly (P = 0.05). There were
no differences in aluminium contents of mature leaf
due to the use of NPKS 25:5:5:5 or NPK 20:10:10
(Table 1). The aluminium contents of mature leaf
did not respond to different rates of potash (as
muriate of potash) fertilizer (Table 2).
Increasing rates of nitrogen did not significantly
increase the aluminium soil contents at all depths
Table 1. Effects of different rates and sources of nitrogen (as NPKS 25:5:5:5 and NPK 20:10: I0) on the mature tea leaf and soil
aluminium contents (ppm)
Rates and sources
(kg N ha- 1. year - l )
Soil A1 contents at different soil depths
0-10 cm 10-20 cm 20-30 cm
NPK 20: I0:I0
LSD P = 0.05
r ~ - 0.85 b 0.82 0.71 0.40
correlation coefficient of linear regression analysis between rates of nitrogen and aluminium contents of mature leaf and soil.
b significant at P = 0.05.
344 Short communication
Table 2. The effects of different rates of nitrogen (as sulphate of
ammonia) and potassium (as muriate of potash on the mature
leaf aluminium contents (ppm))
Experiment II Experiment III
KgN ha-l. year -~
Kg K2Oha-I. year -1
C.V. % 10.8 8.9
LSD P = 0.05
- 0.95 c
a linear regression coefficient for rates of N and aluminium
contents of mature leaf.
b linear regression coefficient for rates of K20 and aluminium
contents of mature leaf.
c significant at P = 0.05.
studied. However, there was a significant linear
relationship between applied nitrogen and soil
aluminium contents at 0-10cm soil depth in Ex-
periment I (Table 1). Generally, increasing rates of
nitrogen seemed to improve the levels of available
(exchangeable) aluminium in the soils.
The availability of exchangeable aluminium is
known to be high in acidic soils. Increasing rates of
nitrogen normally increase the soil acidity
(Bhattachavya and Dey, 1983; Sivasubramanium
and Talibudeen, 1972) and this explains the mar-
ginal increase in the levels of available exchange-
able aluminium with increase in nitrogen fertilizer
rates. This increase in the soil available aluminium
was expected to increase the uptake of aluminium
by the tea plant. However, an increase in the rate of
nitrogenous fertilizers had an opposite effect. The
decrease in aluminium uptake due to increasing
rates of fertilizer is attributed to the competition in
uptake between ammonium and aluminium ions
(Kotze et al., 1977).
Earlier it had been thought that high rates of
nitrogen in tea might influence uptake of
aluminium by tea to levels which would make teas
unsuitable for consumption and hence be detri-
mental to tea quality. This study has demonstrated
that the use of high rates of nitrogen is one of the
means of reducing aluminium uptake by the tea
bush. Indeed, the aluminium contents of black tea
were recently demonstrated to decrease with in-
crease in nitrogenous fertilizer rates (Owuor et al.,
Edmonds and Gudnason (1979) had observed
that addition of aluminium salts (i.e. high levels of
aluminium) in the fermenting "dhool" improves
the visual look of resultant black tea and hence its
value. Increasing rates of nitrogen were noted to
reduce the amounts of aluminium in the mature
leaf, and also in black tea (Owuor et al., 1989). This
will therefore tend to reduce the valuations of these
Although increasing rates of nitrogen decreased
the mature leaf aluminium contents, the levels of
aluminium in the tea plants were still above the
limit where lack of aluminium retards the growth of
tea (Ishigaki, 1984). Thus yields of tea in Kenya are
not likely to decrease due to the reduction of
aluminium uptake. This study has demonstrated
that the use of high rates of nitrogen may be
causing some nutritional imbalance in the other
nutrients which may in the long run be difficult to
correct. Thus, although good yield responses have
been recorded due to nitrogenous fertilizer usage,
the fertilizers should be used with caution.
Data collection by staff of Chemistry Depart-
ment, Tea Research Foundation of Kenya,
(TRFK) is acknowledged. This communication is
presented with the permission of the Director,
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