Nutrient status and fertilizer responses of oil palms on

Nutrient status and fertilizer responses of oil palms
on different soils in the forest zone of Ghana
H. A. M.
VAN DER
VOSSEN
Oil Palm Research Centre, Crops Research Institute, P.O. Box 43, Kade, Ghana
SUMMARY
Climatic requirements and topography restrict
economic oil palm production in Ghana mainly to the
Forest Oxysols and Forest Ochrosol-Oxysol Intergrades
developed over granites, LowerBirrimian rocks (phyllites)
and a relatively inextensive area (520 km2) in the extreme
south-western part of the country of Oxysols over
Tertiary sands. 8-12 years' yield records of seven 25
and 24 factorial fertilizer trials (planted in 1954-57),
together with foliar analysis data taken from these trials
and other experimental fields, have shown P and K
deficiencies in oil palms on soils of all three geological
formations. Consistent and highly significant yield
responses of 30-35 % to phosphate fertilizer applications
were found in an experiment on soils over Tertiary
sands (Aiyinasi) and in one trial on soils over granites
(Assin-Foso), while both experiments also showed a
significant K effect in some years. A PK interaction by
which responses to potash fertilizers became highly
significant (20% yield increase) in presence of added P
was found in another trial on soils over granites (Pretsea).
Incidental N effects, KMg and other interactions in
various trials are discussed. The sharp yield decline
after the 5th-6th year of production in the experiments
at Aiyinasi (Tertiary sands), in contrast to more stable
yield levels at Bunso (11-15 t/ha) and other stations,
indicates that under conditions of light soils, and
excessively high rainfall special precautions have to be
taken to preserve a satisfactory fertility status of these
soils. Tentative recommendations on type, rate and
frequency, time and method of fertilizer application
are given.
Original scientific paper. Received 30 Apr 70; revised
13 Jun 70.
RESUME
H. A. M. VAN DER VOSSEN: Qua/ites
nutrltlves et
reactions d l'emploi d'engrais pour les palmiers d huile en
divers sols de la zone forestiere du Ghana. Les necessites
climatiques et la topographie limitent la production
economique du palmier a huile au Ghana principalement
aux Forest Ochrosols et Forest Ochrosol-Oxysol
Intergrades sur les granites, roes Lower Birrimians
(phyllites) et a une zone relativement peu etendue
(520 km2) a l'extreme partie sud-ouest du pays d'Oxysol
sur sables tertiaires. Des resultats portant sur huit a
douze ans de recoltes de sept essais d'engrais ayant des
factorielles de 25 et 24 (implantees de 1954 a 1957),
ainsi que des donnees d'analyse foliaire provenant de
ces essais et d'autres parcelles experimentales, ont
revele des deficiences en Phosphore et en Potasse parmi
les palmiers a huile cultives sur les sols des trois formations geologiques. Des reactions de productivite stables
et hautement significatives de 30 a 35 % a l'emploi
d'engrais phosphates ont ete constatees lors d'experimentation sur sols a base de sables tertiaires (Aiyinasi)
et lors d'un essai sur sol a base de granite (Assin-Foso),
alors que les deux essais ont egalement revele un effet
significatif a la potasse pendant certaines annees. Une
action reciproque Phosphore/Potasse au cours de laquelle
les reactions aux engrais potasses (20% d'augmentation
de productivite) en presence d'un apport de Potasse fut
constatee lors d'un autre essai sur sols a base de graIiite
(Pretsea). Les reactions fortuites de I'Azote,du Potassium
/Magnesium et autres actions reciproques lors de divers
essais font l'objet d'une discussion. Le declin brutal de
productivite apres la 5eme ou 6eme annee de production
durant les essais d'Aiyinasi (sables tertiaires), contrastant
avec les niveaux constants des recoltes a Bunso (11 a
15 t/ha) et dans les autres stations, prouvent qu'avec
des sols legers et une pluviometrie excessive, il faut
prendre des precautions speciales pour maintenir un
etat satisfaisant de fertilite avec de tels sols. Des recommandations faites a titre de suggestions sont formulees
concernant Ie type, Ie taux et la frequence, l'epoque et la
methode d'apport d'engrais.
Accra: Ghana Universities
Press
I
H. A. M. van der Vossen (1970) Ghana Jnl agric. Sci. 3, 109-129
Introduction
Exploratory oil palm fertilizer trials of a 25 and
4
2 factorial design were established at various
agricultural stations and on one oil palm plantation
in the forest zone of Ghana between 1954 and
1957. The results of these experiments, together
with available soil and leaf analysis data, are
discussed below in an attempt to assess the major
nutrient requirements of oil palms grown on
different types of soil and under various climatic
conditions in the forest zone.
The forest zone which covers a third of Ghana
(or about 82 000 kmz) in the southern part of the
country is divided, according to its original
vegetation, into (1) a rainforest zone (CynometraLophira-Tarrietia association) of about 7000 krnz
in the extreme south-west; (2) a moist semideciduous forest zone (Celtis-Triplochiton association) of about 48 000 kmz including a narrow
transition zone between the latter and the rainforest; and (3) a drier semi-deciduous forest zone
(Antiaris-Chlorophora association) to the north and
east of the moist semi-deciduous forest zone,
continuing in a comparatively narrow stretch northwards into the Volta Region (Lane, 1962). These
vegetational zones reflect the climate, in particular,
total rainfall and its distribution over the year. The
climatically suitable areas for oil palm cultivation
are, therefore, mainly within the first two zones.
The soil parent material in the forest zone
consists for about 99% of Pre-Cambrian rocks,
predominantly Lower Birrimian formations (phyllites with occasional greywacke, tuffs and associated
schists) and granites (Bates, 1962). The topography
over these two geological formations is normally
gently rolling. The Upper Birrimian formations
(volcanic rocks) have a much steeper relief, while
the belt of Tarkwaian rocks is much more rugged
with very steep slopes (Brash, 1962). The soils
developed over Lower Birrimian rocks and granites
are thus from a topographical point of view considered the more suitable ones for oil palm development. Brash (1962) remarks that the topography
of similar geological formations is always more
strongly dissected in the south-western part of the
forest zone where rainfall is highest. Deposits of
Tertiary sands are confined to a small area of
about 520 kmz in the extreme south-west. The
fairly flat upland is here dissected by steep valleys
(Ahn, 1961). These Tertiary sands are a continuation of similar deposits which cover the southeastern part of the Ivory Coast where the main
oil palm station ofIRHO (L'Institut de Recherches
pour les Huiles et Oleagineux) and some of the
larger industrial oil palm projects are situated. The
geological formation of a small area around
Jasikan and Akaa (Volta Region) which is climatically just suitable for oil palm cultivation is PreCambrian Arkosic sandstone.
The soil texture of the major upland soils derived
from phyllite is clay to silty light clay with frequent
to abundant quartz gravels and ironstone concretions in the subsoil. Upland soils over granites
are sandy to gritty light clays frequently with
gravels in the subsoil. On both geological formations
the colluvial soils, relatively inextensive, are free
from gravels apart from an occasional stoneline
at 100-120 cm depth between subsoil and weathered
substratum (Ahn, 1961). The deep and uniform
sandy to sandy light clay soils developed over
Tertiary sands are usually free from gravels.
The soils in the forest zone are for the greater
part free-draining Latosols. The forest Latosols
were divided by C. F. Charter into two Great Soil
Groups, Forest Ochrosols and Forest Oxysols,
each with a characteristic reaction profile (Charter,
1955; Brammer, 1962). The distribution of the
Oxysols coincides with the rainforest in the southwest, where rainfall exceeds 1800 mm per annum.
These soils are strongly leached and have a very
acid surface horizon (pH below 5). The Ochrosols
which have a near neutral to moderately acid
topsoil reaction (pH over 5·5) are the most widely
distributed group of soils in the forest zone of
Ghana. There are broad transition zones of
Ochrosol-Oxysol intergrades with intermediate
characteristics.
Mature Forest Ochrosols are
generally more fertile than Oxysols, mainly
because they are less leached of their exchangeable
bases. While the majority of the cocoa in Ghana
is produced on Forest Ochrosols (Charter, 1955),
successful oil palm cultivation depends to a lesser
degree on the inherent fertility of the soil. The oil
palm is in fact very tolerant of soil acidity (Tinker,
1962). Those areas climatically favourable for oil
palm cultivation (van der Vossen, 1969) actually
coincide largely with the distribution of Forest
Oxysols and Ochrosol-Oxysol intergrades.
Description
of the experiments
Design, site and soil data for each of the seven
experiments have been summarized in Table 1.
The fertilizer trials at Aiyinasi (801-1) and Bunso
(810-1) were planted with the direct advice of the
West Mrican Institute for Oil Palm Research
(WAI FOR, now NIFOR) while the experiments
at Assin-Foso (809-1), Kwadaso (821-1), Bechem
(822-1) and Akaa (831-2) were originally laid down
by the Ghana Department of Agriculture but
incorporated also in NIFOR's programme of
fertilizer trials in 1959. The Oil Palm Research
Centre (OPRC) took over the control of these six
experiments in 1965, although weekly yield
records continued to be submitted to NIFOR.
Experiment 805-1 was laid out in 1959 in a 1957
planting of the oil palm plantations at Pretsea
with advice from PAMOL (Cameroon) Ltd. The
OPRC took over the control of this experiment in
1965.
In all these experiments the elements N, P, K
and Mg and, in the case of 801-1 and 810-1, Ca
as well, are tested at two levels (0, 1) in simple
factorial designs. The statistical design of experiments 809-1, 821-1 and 831-2, a single replication
of a 24 confounded factorial, is in fact unsatisfactory as it leaves only 4 degrees of freedom for
the 'error' variance. Only very striking treatment
effects can be detected.
The treatment plots of all the experiments are
surrounded by complete guardrows and are
arranged in blocks of eight plots by confounding
the interaction(s) of highest order with blocks.
The six WAIFOR experiments were planted
with dura X dura extension work seed from that
Institute, the planting distance being 8·8 m (29 ft)
triangular (147· 8 palms per ha). Planting material
in experiment 805-1 at Pretsea is (Deli) dura X
pisifera e.w.s. from PAMOL (Nigeria) Ltd. The
planting distance is here 9·1 m (30 ft) triangular
or 138·1 palmsjha.
Method of fertilizer application. Fertilizers were
applied according to the 'pound-per-palm-peryear-of-age' principle at Bunso and Aiyinasi up to
1960 (6 years after planting), at Assin-Foso and
Kwadaso up to 1961 (6 years after planting), at
Bechem and Akaa up to 1962 (5 years after planting). This principle involves applying t lb at
planting, 1 lb during the 1st year after planting
and so on until the 6th year when each palm
receives 6lb of each fertilizer (according to plot
treatment). At the advice ofNIFOR, frequency of
fertilizer application was then changed to a
triennial schedule for P, K, Mg and Ca, while N
continued to be applied annually. In years of
complete fertilizer applications each palm received
according to treatment: 4 lb sulphate of ammonia
(N), 10 lb single superphosphate (P), 5 lb muriate
of potash (K), 6 lb Epsom salts (Mg) and, in the
case of experiments 801-1 and 810-1, also 7lb
lime (Ca). In the two subsequent years only 4 lb
sulphate of ammonia per palm were applied in the
N1 plots.
The application of fertilizers did not follow a
regular pattern in experiment 805-1 at Pretsea.
All the palms received in 1957 and 1958 a PKMg
fertilizer mixture as the actual fertilizer trial was
started in the 2nd year after planting. The following fertilizers were applied per palm according to
plot treatment in 1959, 1960 and 1963: 2 kg
sulphate of ammonia, 2 kg superphosphate, 2 kg
muriate of potash and 1 kg kieserite. Fertilizer
applications were resumed in August, 1968, after
an interval of 4 years due to the unavailability of
fertilizers.
In all the experiments fertilizers were broadcast
in a broad ring around the palms in May, i.e.
at the beginning of the main wet season.
Results and discussion
Some of the earlier results of the six WAIFOR
fertilizer trials have been published in the annual
reports of that Institute (NIFOR, 1958-1966).
Because of indications that errors might have been
made in compiling the records, it was decided to
re-analyse all the data after recompiling the yield
records from the original weekly field notebooks.
Statistical analysis was carried out on the annual
and triennial yield totals, both for number of
bunches as well as total bunch weight.
The coefficient of variation was greatly reduced
by averaging yields over more years. The climatej
treatment interaction, which plays an important
role in the annual yield variation but in the statistical analysis of variance forms part of the error
variance, is apparently reduced considerably by
taking running means over some years. In accordance with earlier observations by Haines &
Benzian (1956) and Chapas (1961) of the existence
TABLE
Data on Experimental Site
Station
I
Region
Expt
no.
Aiyinasi
Western
801-1
1954
6
Pretsea
Western
805-1
1957
11
AssinFoso
Central
809-1
1955
4
Bunso
Eastern
810-1
1954
Year
planted
Ha
Previous
history of
area
Av. annual
rainfall
(mm)
I
I
\
Palms
per
plot
Statistical
design
I
II
Single repl. of 25
confounded factorial,4 blocks of
8 plots
15
Two repl. of 24
confounded
factorial, 2 blocks
of 8 plots per repl.
24
1750
Scattered
cocoa and
food farms
Single repl. of 24
confounded
factorial with
2 blocks of8
plots
16
1670
6
Old secondary
forest
25 as 801-1
15
1850
2
Young
secondary forest
24 as 809-1
8
1560
16
1420
15
1530
Young
secondary
forest
Bush regrowth
I
2370
I
I
Kwadaso
Ashanti
821-1
1955
I
Bechem
BrongAhafo
822-1
1957
4
Old secondary
forest
24 as 809-1
Akaa
Volta
831-2
1957
4
Medium aged
secondary
forest
24 as 809-1
I
of distinct 3-year cycles in oil palm yields,
over 3 years were taken. The analysis of
of total bunch weight gave equal or higher
significance for treatment effects compared
I
I
averages
variance
levels of
with the
analysis of bunch number, and the latter did not give
much additional information either. The results are
therefore presented in the tables as total bunch
weight in kgjhaj annum averaged over 3-year periods.
Climate
Soils
I
Mean annual
water deficit
(mm cv %)
I
Parent
material
I
I
Great soil
group
221
90
Tertiary
sands
Oxysols
326
46
Granites
(Dixcove
type)
I OchrosolOxysol
intergrades
I
Soil type
(local series)
Texture
References
for description
of soil
series
Coarse
material in
subsoil
Sedentary
(Tikobo)
Sandy loam
to sandy light
clay
No gravels
Ahn,1960
Sedentary
(AgonaNkwanta) with
colluvial
soils at one
end (NtaAkroso)
Sandy to
gritty light
clay
Frequent
ironstone
concretions
and gravels in
sedentary soils
Purnell, 1960
223
35
Granites
(Kumasi
type)
Ochrosols
Sedentary
(NsabaSwedru) with
minor section
over colluvial
soils (NtaAkroso)
Silty to gritty
light clay
Frequent
ironstone
concretions
and gravels
in sedentary
soils
Asamoa, 1964
192
38
Lower
Birrimian
phyllites
OchrosolOxysol
intergrades
Colluvial
(Kokofu)
Silty clay
No gravels
except for a
thin layer of
quartz stones
at 90-120 cm
Obeng,1959
254
32
Granites
(Kumasi
type)
Ochrosols
Sedentary
(KumasiAsuansi) with
minor section
over colluvial
soils (Akroso)
Sandy to
gritty light
clay
Occasional to
abundant
quartz gravel
i
)
I
I
I
377
30
Granites
(Dixcove
type)
Ochrosols
Sedentary
and colluvial
Sandy to
gritty loam
Occasional
quartz gravel
313
17
Arkosic
sandstones
of Buem
formation
Ochrosols
Colluvial
(Afeyi)
Sandy loam
Occasional
pieces of
subangular
Arkosic sandstone below
70-80 cm
Leafsamples were taken in 1962, 1965, 1969 and
analysed by NIFOR. The foliar analysis data,
which are presented in the tables along with
the yields, indicate the nutrient content as a
Mould, 1957
percentage of dry matter for leaf 17. Critical
levels referred to in the following pages are those
used for mature palms by IRHO (1962) and
NIFOR (1963).
H. A. M. van der Vossen (1970) Ghana JnJ agric. Sci. 3, 109-129
2
TABLE
Expt 801-1 (Aiyinasi). Effect of N, P. K, Mg and Ca Fertilizers on Yield and Leaf Nutrient Content for the
Period 1958-1969
Leaf nutrient content
0 dry matter leaf 17)
Yields
total bunch weight (kgjhajannum)
Level of
fertilizer
I
1958-60
No
N1
Po
P1
Ko
K1
Mgo
Mg1
Cao
Ca1
(';<
1964-66
1961-63
12037
12228
10562
13703***
11844
124221)
12302
11963
12106
12160
8190
8036
6823
9403***
8244
7982
8130
8096
7992
8234
7761
8211
6953
9018***
7572
8400*
8009
7963
8020
7952
I
3821
4380*
3559
4642***
3965
4236
4229
3972
3918
4283
1965
av.16
plots
1962
av.5
plots
1967-69
N
P
K
Mg
Ca
2·25
2·79
I
2·91
2·27
i
0·134
0·133
0·139*
0·150
0·82
0·87
1·07
1·09**
0·36
0·31
0.36
0·34
0·93
0·95
0·97
0·97
Interactions:see (2)and (3)
LSD
P = 0·05
P = 0·01
P = 0·001
cv %
773
1078
1510
870
1213
1700
12
9
614
856
1200
508
709
993
10
16
\
(1) K main effectand PK interactionsignificantat P<0·05
in 1962
(2) Effect of phosphate fertilizerapplications on leaf K and Ca
I
Po
P1
0·93
0·82
1965
1969
1·08
0,88**
0·96
0·79**
I
1962
1965
1969
0·88
0·99
0·91
1,00***
0·67
0·68
I
2·44
2,54*
*
**
Significantat P<0·05
Significantat P<O·Ol
*** Significantat P<O·OOl
LSD
cv
0·35
0,30***
= leastsignificantdifference
= coefficientof variation
0·44
0·39***
1969
av.16
plots
2·42
2,55**
0·138
0,147*
0·75
1,01***
0·41
0·42
0·67
0·68
Experiment 801-1 at Aiyinasi
The results of this experiment, in which production started in 1958, are summarized in Table 2.
Yield responses to phosphate fertilizer applications,
always highly significant, have been about 30%
throughout the whole 12-year period. The effect
of potash fertilizers on yield was statistically
significant in 1962 and over the period 1964-66,
while there was also an indication of a positive PK
interaction
(significant at P<O'l)
in 1962.
Phosphate and potash fertilizers combined gave
over the period 1958-69 a yield increase of 37%
Applications of nitrogenous fertilizers resulted in
a significant and positive yield response during the
last 3-year period only.
Yields over the first 5 years of production,
especially in the P1K1 plots, were high by usual
standards, as can be seen from the diagrammatical
presentation of the effect of phosphate and potash
fertilizers on annual yields in Fig. 1. The spectacular and persistent yield decline, in the fertilized
as well as in the control plots, from the 6th year
of production is in total contrast to the earlier
promising results.
Supervision in the oil palm section at Aiyinasi
has been adequate throughout the whole period.
It is therefore very unlikely that poor harvesting
and yield recording practices are major causes of
the yield decline in expt 801-1, as has definitely
been the case in some trials at other stations
(notably expts 821-1 and 831-2, see page 123).
The healthy appearance of the palms indicates that
incidence of diseases and pests does not play a
significant role either. No outbreak of the leaf
miner pest (Coelaenomenodera elaeidis), which
poses real problems to the oil palm plantations at
Pretsea and Sese, only about 100 km to the east
of Aiyinasi, has been observed as yet. The rhinoceros beetle (Oryctes spp.) although somewhat
more abundant at Aiyinasi than at other stations,
probably due to intensive coconut cultivation in that
area, has caused only occasional light damage in
the oil palm experiments. An explanation must
therefore be sought in a very deficient and unbalanced mineral nutrition aggravated in some
years by an unfavourable change in climate.
The foliar analysis data (Table 2) indicate that,
in order of importance, P, K and N are the deficient
X 103 KG/HA
/6
E·S·
HRS/A-...
1900
1958
C
1959
C
1960
eN
1961
1962
N
1963
eN
1964
1965
N
1966
eN
1967
1968
C
I969YEAR
C
Fig. I. Expt 801-1 (Aiyinasi). Mean effect of P and K fertilizer applications on total bunch weight per annum. Applications
of all fertilizers (C) or sulphate of ammonia (N) alone has been indicated for each year at bottom of graph. £.5. =
effective sunshine over the corresponding
period, i.e. 28 months before year of harvesting.
nutrient factors. Leaf P, although significantly
increased by phosphate fertilizer applications,
could not be restored to above the critical level
(= o· 15%) after 1962. Potash fertilizers also
increased leaf K significantly. The significant
negative effect of phosphate fertilizers on leaf
K is explained by the fact that yields are much
higher in the PI plots. Large quantities of K
are immobilized in the bunches (Werkhoven, 1966)
and the increased exportation of K by higher bunch
production will be at the expense of the leaf K
content when not sufficiently compensated by the
naturally available K in the soil or by potash
fertilizer applications. The leaf K figures for
1969 given below demonstrate this effect clearly:
the leaf K content remains under the critical
level (= 1· 00%) in the PI K1 plots.
Po Ko: 0'81% PI Ko: 0·67% (averages over 8
plots)
Po KI: 1'11% PI KI: 0·90%
Leaf N was at a very satisfactory level in 1962
while applications of nitrogenous fertilizers restored the leaf N content significantly to above the
critical level (= 2· 50%) in 1969, this being reflected
in a positive yield response. The very low leaf N
levels for 1965 are in fact in no relation with the
leaf analysis data of 1962 and 1969, and there is no
explanation other than that errors might have been
made during sampling or analysis work.
The positive effect of phosphate applications on
leaf Ca is likely to be due to the Ca content
(18-21 %) of the single superphosphate.
The
common antagonistic effect of potash applications
on leaf Mg is demonstrated again by these data,
while the positive effect of potash fertilizer
applications on leaf N is in accordance with the
existence of a positive correlation between leaf N
and leaf K as reported by Forde, Leyritz & Sly
(1968). Leaf Mg remained above the critical level
(= 0·24%) even in the KI Mgo plots. Leaf Ca
decreased gradually in the course of the years but
always exceeded the critical level (= 0·60%). It
is therefore not surprising that the interactions
PCa and KMg were not reflected in the yields.
The leaf analysis data show that the phosphate
and potash fertilizer applications have been
inadequate
to maintain a balanced mineral
nutrition.
Sunshine and rainfall distribution are normally
sub-optimal for the oil palm in West Mrica and
form limiting factors for maximal production.
Sparnaaij, Rees & Chapas (1963) demonstrated the
existence of a high and positive correlation between
yields and effective sunshine (E.S.), defined as
total amount of sunshine hours during periods
of soil moisture sufficiency 28-30 months earlier.
However, from the graphs in Fig. 1 it can be seen
that the fluctuations and downward trend in E.S.
are not reflected proportionally in the yields. The
correlation coefficient for E.S. and yield averaged
over the PI KI plots for the period 1962-69, being
o . 68 and significant only at P < 0 . 1, indicates that
the E.S. yield relation is less pronounced when
other yield-limiting factors, in this case P and K
deficiencies, become prominent.
As a consequence of Liebig's law of the minimum a significant positive correlation can be
expected between leaf content of a nutrient and
yields when this nutrient is both deficient and at
the same time the most important yield-limiting
factor (Prevot & Ollagnier, 1961). Phosphorus was
thus the dominant deficient factor in 1962/63 and
1969, as can be inferred from Table 3 below. The
sample number for K in the PI plots (n = 5 in
1962 and n = 16 in 1969) is unfortunately too
low to show significant correlations but the correla3
TABLE
Correlation between LeafP, K and Yield in Expt 801-1
1--I
Leaf factor
_______
P (all plots)
K (all plots)
K (Pl plots)
.__
I 1965
1962
0·73*
.. -0·12
..
0·61
••
1
1
0·75* (n
-0·05
0·63
= 10)
(n=10)
(n = 5)
I
0·12
-0·31
I 0·35
i
1965/66
0·29 (n = 32)
0·26 (n = 32)
0·35 (n = 16)
Nutrient status and fertilizer responses of oil palms in Ghana
117
TABLE 4
Analytical Data of Surface Samples (0-15 cm)from Tikobo Soils at Different Sites (a) and in Expt 801-1 after 10 years
Oil Palm Cultivation (b)
I
I
I
Sample
Reference
I
(a) 1955
(b) 1965
Exchangeable bases m. e./l00 g
..
. '1
Ahn,1961
Forde, 1966
K
C.E.c·l
I
Mg
I
0·09-0·12
0·04
4-5
2·13
1
tion coefficients at least indicate that K will be the
second important yield-limiting nutrient factor,
once the leaf P status is corrected.
The dominant limiting factor in 1965 and 1966
appears to have been the very low E.S. (1422 and
1341 h resp.) over the corresponding periods, and
this suggests a reason why there was a total lack
of a significant correlation between leaf nutrient
levels and yields, although leaf P and K were
certainly deficient. Ruer (1966) demonstrated that
significant correlations between leaf K or leaf N
and yield disappeared in years with a corresponding
E.S. below 1600 h per annum.
A composite soil sample taken in March 1965
from the top 15 cm in the 16 Po plots in expt 801-1
was among the 17 samples from various parts of
West Mrica used in a pot experiment at NIFOR
to study the phosphorus status of these soils
(Forde, 1966). Available P determined by various
extraction methods was extremely low for the
Aiyinasi soil sample, about the lowest of the 17,
thus indicating the very low P status. Total P
was only 96 ppmjlOOg soil. When comparing also
the other analytical soil data for the 1965 soil
sample presented by Forde (1966) with averages of
nine surface samples of the same Tikobo soil
series taken by Ahn (1961) at different sites within
the Tertiary sands area at the time that expt
801-1 was established (see Table 4), it is clear that
the soil in this fertilizer trial has now a much lower
nutrient status than would be normal for comparable soils in that area. The major cause must
have been a considerable loss in organic matter
content of the topsoil, since cation exchange
capacity, P and N content, already low in these
highly leached sandy soils, are closely related to
the amount of organic matter (Ahn, 1961).
The nutrient status of the soil was apparently
sufficient to support high yields during the first
I
0·24-0·47
i
0.12
I
C
Ca
0·30-0·35
0·74
I 0"
I
I
,0
1·06
0·70
I_~
pH
1 _~_I
0/
I
0·07
0·07
___
-
I
I
4·6-4,9
I
5 years of production, especially when the major
deficient nutrient factor P had been corrected.
The development of a very extensive root system,
favoured by the light texture of the soil, enabled
the palms to exploit large volumes of soil, thus
compensating for an initial loss in soil fertility.
The sharp drop in yield since 1963 suggests that,
due to the consistent decrease in organic matter
content and depletion of available nutrients by
root uptake, leaching and P-fixation, the nutrient
status had deteriorated to below a minimum
required to support high bunch production. This
downward trend in production was accentuated
further by the negative effect of low effective
sunshine especially for the years 1965, 1966 and
1968.
In a recent review on the role of trace elements
in the nutrition of the oil palm, Forde (1968)
showed that significant responses to applications
of micro-nutrients have been infrequent and highly
variable. Definite critical levels or well defined
symptoms for micro-elements are not known for
the oil palm. It would therefore be highly speculative to suggest that the downward trend in yield
of this experiment was due to deficiencies in one
or more micro-elements.
Although fertilizer applications gave significant
yield responses, it is clear from the sub-critical
leaf P and leaf K levels after 1962, even in the
plots receiving these fertilizers, that the triennial
method of application is unsuitable for these acid
soils with an extremely low C.E.C. A part of the
applied nutrients was apparently leached out, or
fixed in the case of phosphorus, before it became
available to the palms.
A more balanced mineral nutrition for these soils
might perhaps be achieved by a change to annual
applications of all fertilizers and also by a shift
of the time of application from May to August
TABLE
5
Expt 810-1 (Bunso). Effect of N, P, K, Mg and Ca Fertilizers on Yield and Leaf Nutrient Content over the Period
1958-1969
I
I
Leaf nutrient content
Yields
total bunch weight (kglhalannum)
Level of
fertilizers
1958-60
1961-63
(% dry matter in leaf 17)
1964-66
1967-69
1969 avo 16 plots
I
No
N1
Po
PI
Ko
K1
Mgo
Mg1
Cao
Cal
Interactions
LSD
P
cv %
=
0'05
I
I
I
9443
9797
9463
9776
9269
9708
9513
9727
9820
9419
(2)
I
I
I
1091
I
15
I
I
13101
13543
13464
13180
13044
13600
13078
13566
13277
13367
12304
12936
12648
12592
12387
12853
12404
12836
12766
12474
11463
120561)
11662
11858
11463
12056
11733
11786
11845
11674
710
1097
1033
7
12
12
I
I
I
II
I
2·41
2·37
0·142
P 0·145
0·83
K
0'93*
0·39
Mg 0.41
0·51
Ca
0·55
(3)
N
I
I
(1) There was a significant (P<O '05) positive N main effect in 1967
(2) KMg interaction was positive and significant (P<O '05) for 1958-60
9791
9235
8747
10707
I LeafK
Po
PI
0·93
II 0·83*
9269
9708
LeafMg
Ko
K1
0·42
0'37*
I
to avoid excessive leaching of the more soluble
fertilizers during the month of June when rainfall
is very high (in some years > 700 mm). The low
content of exchangeable Mg in the soil in later
years (see Table 4) indicates that Mg may become
deficient if not added because of the antagonistic
effect of potash applications. The leaf Ca status
is satisfactory and extra doses apart from the Ca
already applied together with single superphosphate are apparently not required. Annual
application started in August 1968 and the design
of the experiment was altered in 1969 to a 4 X 23
factorial (NPKMg) with K at 4 levels by leaving
out the Ca factor. It is expected that by a regular
application of fairly high doses of the major
nutrients the yields in the fertilized plots will be
raised to the 1963/64 levels or slightly higher
(9-11 t/ha/annum) in years with corresponding
effective sunshine exceeding 1600 h. Yields may
not be restored to the high levels of 1961/62 even
in climatically optimal years, because of the
irreversible loss in organic matter which influences
the nutrient storage capacity in these sandy soils.
Experiment 810-1 at Bunso
In contrast to the fertilizer trial at Aiyinasi a
high level of production was maintained in expt
810-1 over the whole 12-year production period,
with no significant main effects except for a
significant positive K effect in the presence of added
Mg during the first 3-year period (Table 5).
There are no soil analytical data available, but
the nutrient status of this clayey colluvial soil
(Forest Oxysol-Ochrosol intergrade) derived from
Lower Birrimian phyllite was apparently good
enough to support these high yields for many years
even without added fertilizers.
Leaf samples were taken only once in 1969.
These foliar analysis data at least indicate that
there has been a gradual depletion of some of the
major nutrients and that this was insufficiently
compensated by the current method of fertilizer
applications. Leaf N, P and K were below the
critical level also in the plots receiving that
particular fertilizer. Only potash applications had
significantly raised the leaf K content. There was a
negative effect of phosphate applications on leaf
K, although less pronounced than in expt 801-1:
Po Ko: 0·86% PI Ko: 0·80%
Po K1: 0·99% PI K1: 0·87%
The absence of any significant correlation
between leaf N, P or K and yields probably
indicates that none of the deficiencies was severe
enough as yet, or that the leaf nutrient levels have
only recently started to become sub-critical and
that correlations will exist with yields in 1970 or
1971 (Ruer, 1966). There is nevertheless already a
considerable drop in yield in 1969 (see Fig. 2)
which is probably a first reflection of the lower
nutrient status. When viewed separately the 1969
yield data showed already an indication of a
positive K and Mg main effect (significant at
P <0· 1). The available climatical data do not
suggest an unfavourable change in effective sunshine as a factor causing the yield decline in 1969,
as has apparently been the case for the 1966 yields.
X 103 Ko/HA
16
15
1958
C
1959
C
1960
eN
.961
.962
N
1963
eN
1964
1965
N
1966
eN
1967
1968
N
1969YEAR
C
Fig. 2. Expt 810-1 (Bunso). Mean effect of K and Mg fertilizer applications on total bunch weight per annum. Cor N
dressings (see caption of Fig. I) are indicated.
4
6
TABLE
Expt 805-1 (Pretsea). Effect ofN, P, K and Mg Fertilizers on Yield and Leaf Nutrient Content for the Period 1961-1969
Yield
total bunch weight
(kgjhajannum)
Level of
fertilizers
No
N1
Po
PI
Ko
K1
Mgo
Mg1
Leaf nutrient content
(% dry matter leaf 17)
1961-63
1964-66
1967-69
1969 avo 5 plots
8764
8531
8201
9094t
8560
8735
8803
8492
9451
9260
9075
9636
9021
9690
9753
8958
8584
9250
8400
9434
8118
9715*
9043
8791
(1)
(2)
2·35
2·42
0·151
P
0·159
0·61
K
0·74
0·48
Mg 0.51
Ca 0·57
(9 plots)
807
978
1340
986
1195
1636
1112
1347
1845
15
17
16
Interactions
N
LSD
P = 0·1
P = 0·05
P = 0·01
cv %
!
9468
8575
8683
10698
9075
9636
8182
8069
8634
10815
8400
9434
Frequency and time of application have been
altered in a similar way as for expt 801-1, with
effect from 1969, while also the design was changed
to a 4 X23 factorial experiment with K at 4 levels.
Experiment 805-1 at Pretsea
Planting density of this experiment is 138 . 1
palmsjha. The yield data as presented in Table 6
and Fig. 3 are, however, production figures
converted to 147· 8 palms Iha to facilitate comparison with other trials.
There was an indication of a positive P main
effect (P<O'I) for 1961/63 and the K main effect
was positive and significant (P<0'05) in 1967/69.
The positive PK interaction is very interesting:
responses to potash fertilizers became highly
significant (P<O '01) with added phosphate
fertilizers for the period 1967/69 and significant
(P<0·05) in 1964/66. The P effect was significant
(P <0· 05) in the presence of K for the whole of the
period 1964/69 (see Table 6). Since fertilizer
applications were resumed only in August 1968,
after an interval of more than 4 years, at least part
of the yield responses during the period 1967/69
must be attributed to the long residual effect of
potash fertilizers (Forde et al., 1968) but also of
phosphate fertilizers on oil palm yields. Mean
bunch production increase of the 16 PI KI plots
over the 16 Po Ko plots for 1962-1969 was almost
20% (Fig. 3).
Foliar analysis data for 1969 samples, from 10
plots only, showed leaf K to be very deficient.
X 10'
The potash fertilizer application in August 1968
did not yet restore the leaf K content to a satisfactory level. The highly significant correlation
between leaf K and yield (Table 7 below) indicates
that K is apparently the dominant deficient factor.
TABLE 7
Correlation between Leaf N, P and K and Yield in Expt
805-1
0·52
0·09
0,82**
**
Significant at P<O ·01
The level of production, already not unsatisfactory when taking into consideration the suboptimal climatic conditions (mean annual water
deficit 325 mm, see Table 1) is likely to be raised
significantly by regular applications of the major
nutrients NPKMg, with emphasis on potash
fertilizer applications.
KGIHA
16
15
14
13
12
II
10
9
8
7
0-0=0
•. --e=
6
5
P
x---x.
IC
6-A=
P+K
4
3
2
1960
C
1961
1968
C
1969 YEAR
C
Fig. 3. Expt 80S-I. Mean effect of P and K fertilizer applications on total bunch weight per annum. C or N dressings
(see caption Fig. I) are indicated.
TABLE
8
Expt 809-1 (Assin-Foso). Effect of N, P, K and Mg Fertilizers on Yield and Leaf Nutrient Content for the Period
1960-1969
Leaf nutrient content
Yields
total bunch weight (kg/ha/annum)
Level of
fertilizers
No
N1
Po
PI
K.
K1
Mg.
Mg1
Interaction
(% of dry matter of leaf 17)
I
1960-63
1964-66
1967-69
2834
3479
2713
3601*
2807
3506*
3173
3141
8955
10232*
8568
10619**
9153
10034
9574
9613
8258
96871)
7549
10396*
8439
9507
9030
8916
1131
1875
1871
3103
1962
2·78
2·81
0·138
P
0,151**
1·14
K
1·06
0·30
Mg 0.31
Ca 1·11
(av. 16 plots)
N
I
(2)
I
I
I
I
1969
2·68
2·71
0·134
0'155**
1·25
1'3~
0·30
0·32
0·79
LSD
P
P
=
=
652
1071
0·05
0·01
I
I
cv %
I
15
9
15
I
I
(1) N main effect significant (P<0·05) in 1968
(2) KMg interaction negative and sign (P<0'05) 1960-63
2457
3888
Experimental 809-1 at Assin-Foso
Notwithstanding the unsatisfactory design (single
repl. of 24), the results have given some very
interesting information about the major nutrient
requirements (Table 8). This experiment had,
however, a very slow start as can be seen in Fig. 4.
Production started only in the 5th year after
planting and yields were very low also in the two
ensuing years. Responses to phosphate fertilizer
applications were nevertheless consistently significant over the whole period 1960-69 and amounted
to about 36% yield increase over these 10 years.
The foliar analysis data of samples taken in 1962
3158
3124
2807
3506
and 1969 show that phosphate fertilizer applications
have adequately restored leaf P, which is very
deficient in the Po plots, to above the critical level.
Phosphorus is apparently the dominant yieldlimiting factor as is indicated by the significant
correlation coefficients for leaf P and yield:
0,60* (n = 16) for 1961/63 and 0,81*** (n = 16)
for 1968/69.
Leaf N and leaf K are considerably above the
critical level even for the No and Ko plots in both
years of sampling. The positive N main effect on
yield which attained significance at P <0' 05
in 1964/66 and 1968 as well as the positive K
Nutrient
status and fertilizer
responses of oil palms in Ghana
TABLE 9
Expt 822-1 (Bechem). Effect DIN, P, K and Mg Fertilizers
on Yield over the Period 1961-69
No significant main effects. Average production in
kg/ha/annum
main effect, significant (P<O '05) in 1960/63,
would suggest that the critical levels (= nutrient
value in the leaf above which one does not expect
yield responses to fertilizer applications) are not
always defined exactly.
1961-63
Experiments 821-1 at Kwadaso, 822-1 at Bechem,
831-2 at Akaa
These three experiments, all of the same unsatisfactory design (single repl. of 24), have given
less information on major nutrient requirements
than the previous four.
Experiment 822-1 showed only for the period
1964-66 a positive NP interaction: response to
phosphate fertilizers was significant in the presence
of added nitrogen. Production level, fairly well
maintained over the whole 9 years (Table 9),
is good when taking into account the sub-optimal
climatic conditions prevalent at Bechem (see
Table 1).
Due to all sorts of circumstances yield recording
of the experiments at Kwadaso and Akaa was
carried out inaccurately during the last few years,
thus making the production figures very unreliable.
Av. 16 plots
cv %
I
7712
17
1964-66
1967-69
11332(1)
8
9496
14
I
(1) NP interaction posltlve and significant (P<O '05)
over the period 1964-66.
No
N,
Mean
Po
PI
Mean
11907
10282
10884
12256
11395
11269
11 094
I
LSD
LSD
I
11570
between any two means in body of table P = 0·05:
1887
between any two means at same border of table
P = 0'05: 1334
See footnotes to Table 2.
XIO'
16 KG/HA
IS
6.
1'~ __
6
1>\', )~---_.~
\ \~
d1/'//
/0
\><--- o----O=-=-=~
0-iJ
.:
0
\
/
""~
~_x_ --x
"~
ti.lf//
1'-
II
/~
///
'/
0
0-0=0
/~~
//
I::>V~/
l(--~
.-_ .• =
=
p
K
6-6:
P. K
0
~ll
~~":/o
i~
1959
c
1960
1961
C
eN
1962
1963
N
1964
eN
1965
1966
1967
N
eN
1968
1969YEAR
C
Fig. 4. Expt 809-1. Mean effect of P and K fertilizer applications on total bunch weight. Cor N dressings (see caption
of Fig. I) are indicated.
H. A. M. van der Vossen (1970) Ghana Jnl agric. Sci. 3. 109-129
TABLE
10
Expt 821-1 (Kwadaso). Effect ofN, P, K and Mg Fertilizers on Yield over the Period 1959-67
Yields
total bunch weight (kgjhajannum)
Level of fertilizers
1959-61
No
N
Po
PI
Ko
K1
Mgo
Mg1
1955
2522
2136
2341
2492
1985
2228
2249
l
I
I
I
1962-66
I
P
=
I
0-05
cv %
7390
6747
6284
7575*
6554
7305
6642
7217
7068
6791
(1)
6855
8226
7054
8027
8070
7011
7416
7665
Interactions
LSD
1965-67
5895
7687
719
1580
23
15
6642
7217
The yield records over the period 1968/69 for expt
821-1 and 1967/69 for expt 831-2 have therefore
been omitted.
Experiment 821-1 showed some interesting
responses to fertilizer applications over the period
1965/67, viz. a significant N main effect as well as
positive and significant KMg and NMg interactions
(Table 10). Yield levels are not high.
The positive and significant yield response to
potash fertilizer applications in expt 831-2 was
persistent over the first 6 years of production
(Table 11). A positive N main effect was significant
only over the first 3-year period. The level of
production over the first 6 years was satisfactory,
when the sub-optional climatic conditions are taken
into consideration (see Table 1).
1107
I
11
I
6981
7157
5588
7994
6284
7575
Nutrient status of oil palms in non-fertilizer
experiments and other plots
Apart from four fertilizer trials, various other
oil palm experiments at Aiyinasi, Bunso and the
OPRC (Kade/Kusi) as well as a 6-acre farmer's
plot near Kusi and samples from scattered subspontaneous palms in a 100-acre block at the
OPRC near Kusi just before clearing and planting
were sampled by leaf analysis early in 1969.
The averages of 2-6 bulk samples, each containing
leaf samples from 10-12 palms, per experiment or
plot, are summarized in Table 12.
The extension work seed comparative trials,
802-1 and 811-1, and the spacing-and-intercropping experiments, 803-1 and 812-1, at Aiyinasi
and Bunso respectively, did not receive any
Nutrient
status and fertilizer
TABLE
responses of oil palms in Ghana
crops in the earlier years. Both experiments showed
also a marked drop in yield after the 6th year of
production.
However, disregarding the usual
annual fluctuations, yields continued to be at the
same level in both experiments at Bunso. Foliar
analysis showed that all major nutrients were in
adequate supply except for P in expt 812-1. Both
experiments were established on well drained light
clay soils developed in river terrace material
(Birim series) over Lower Birrimian phyllite.
The areas sampled at the OPRC are all selection
fields which received annual fertilizer applications
of sulphate of ammonia (up to the 2nd year after
planting) single superphosphate and sulphate or
muriate of potash. Quantities are increased with
age of the palms up to the 4th year when annual
applications of2·3 kg (5Ib) single superphosphate
and 1·4 kg (3Ib) muriate of potash per palm are
started. The satisfactory leaf nutrient content for
all major elements indicate that fertilizer applications have been adequate. It should be noted that
in the young field K1 leaf 9 was taken. Critical
levels for leaf 9 in young palms are fixed somewhat
higher (Bachy, 1964). All fields at Kade and Kusi
are established on sedentary and colluvial soils
developed in Lower Birrimian phyllite. Under the
influence of the fairly high rainfall-about
1700
mm per annum with a mean water deficit of 205
mm-the
reaction profile of these soils is similar
to the Ochrosol-Oxysol intergrades.
11
Expt 831-2 (Akaa). Effect ofN, P, K and Mg Fertilizers
on Yield over the Period 1961-66
Yields
total bunch weight (kg/ha/annum)
Level of
fertilizer
7183
7841*
7748
7277
7212
7811*
7401
7623
No
N
I
Po
PI
Ko
KI
Mgo
MgI
8417
9004
8755
8666
8291
9130*
8581
8839
LSD
P
=
125
0·05
fertilizer applications. The foliar analysis data
thus reflect the natural nutrient status of the soil.
The experiments at Aiyinasi, both on soils similar
to those of the fertilizer trial 801-1, confirm the
earlier conclusions that P and K are the major
deficient nutrients in the soils developed over
Tertiary sands. The low N leaf content in expt
803-1 might be due to inter-cropping with food
TABLE
12
Leaf Analysis Results of Bulk Samples Taken in 1969for Various Oil Palm Experiments and Other Plots
I
Leaf nutrient content in % of dry matter
Station
Expt or Plot
N
Aiyinasi
Aiyinasi
Bunso
Bunso
Kade
Kade
Kade
Kusi
Kusi
i
[
I
I
I
Kusi
I
'[
802-1 (1955)
803-1 (1956)
811-1 (1955)
812-1 (1956)
851-1 (1961)
852-1 (1964)
853 (1966)
K1 (1967)
Farmer's plot
(1962)
K3 semi wild
palms
K
P
2·53
2·33
2·50
2·50
2·62
2·81
2·74
2·77
0·137
0·143
0·152
0·140
0·150
0·152
0·157
0·165
2·45
0·128
I
0·143
I
I
2·67
I
I
.
0·71
0·73
1·06
1·11
1·21
1·32
1·44
1·55
1·06
1·09
I
i
i
I
I
Number
of bulk
samples
Mg
Ca
0·47
0·49
0·39
0·36
0·27
0·37
0·33
0·30
0·68
0·72
0·66
0·60
0·65
0·64
0·76
0·62
4
0·29
0·72
4
0·34
0·75
5
6
4
5
5
2
2
3t
The farmer's plot near Kusi is planted with
dura xpisifera e.w.s. from NIFOR. The leaf
samples of this plot, which was established on
similar soils to those of the experimental fields
but never received any fertilizers, showed a strong
P deficiency. The fairly good leaf nutrient status
of the sub-spontaneous
palms in field K3 is
probably misleading, as these palms produce very
little and exportation of nutrients by bunch
production will be negligible. Leaf P is, however,
also in these palms below the critical level.
The last two sets of samples strongly suggest
a low P status of the soils developed over Lower
Birrimian phyllite. The leaf samples from the
selection fields of the OPRC demonstrate, however,
that this P deficiency can be corrected by regular
applications of phosphate fertilizers to the palms.
Conclusions
The above data have given ample evidence in
some instances of economic yield responses to
phosphate as well as potash and occasionally to
nitrogenous fertilizer applications, while there are
frequent indications of a P deficiency. When the
highly significant P effects which have been
reported from various fertilizer trials established
in Nigeria after 1959 (NIFOR, 1965-68) have been
taken into consideration, it can be concluded that
oil palm yield responses to phosphate fertilizers
are more common than has been generally assumed
for soils in West Mrica (Surre & Ziller, 1963;
Werkhoven, 1966).
The results of the fertilizer trial at Aiyinasi
are in fact in complete contrast to results obtained
by IRHO in the Ivory Coast on soils developed in
similar Tertiary sand deposits and under comparable climatic conditions. The data reported
are almost solely based on one 25 factorial fertilizer
trial planted at the IRHO main station at La Me
in 1946 (Bachy, 1968; 1969). While there is a
total lack of a phosphorus effect, the yield response to annual applications of 2 kg muriate of
potash/palm/annum
are very spectacular indeed:
over the period 1958-68 an average yield increase
in the K1 plots of 59% over the Ko plots which
produced an average of 9 t bunches/ha/annum.
This may indicate that the soils at Aiyinasi are not
typical of the Tertiary sand areas as a whole.
Aiyinasi station is actually sited at the eastern edge
of the deposits of Tertiary sands where they thin
out and are underlain by granite-derived material
(Ahn, 1961).
The results of the oil palm experiments at
Aiyinasi indicate in any case that one has to be
careful in presuming that the soils developed over
Tertiary sands in south-western Ghana would be
highly suitable for oil palm cultivation. Economic
oil palm production for many years on these light
soils combined with very high rainfall can be
obtained only on the conditions that (1) the land
is derived from primary or old broken forest for
an optimal organic matter content in the soil;
(2) a leguminous cover crop is established immediately after clearing to preserve as much as
possible the original fertility status of the soil;
(3) phosphate and potash fertilizers are applied
regularly in fairly high doses supplemented with
nitrogenous and magnesium-containing fertilizers
when necessary.
Soils developed over Tertiary sands are, however, restricted to an area of about 520 km2 and
considerable parts of it are already subject to
intensive coconut and rubber cultivation.
The area over Tertiary sands is thus of minor
importance and oil palm development in Ghana
will have to be concentrated mainly on the soils
developed over granites and Lower Birrimian
rocks within the climatically suitable areas. As
already remarked in the Introduction, the Upper
Birrimian formations and the belt of Tarkwaian
rocks have to be eliminated because of the generally
unsuitable topography.
The nutrient status of Ochrosols and OchrosolOxysol intergrades developed over granites and
Lower Birrimian phyllites is apparently good
enough to support satisfactory oil palm yield levels
for many years without fertilizer applications when
the area is derived directly from heavy forest, as
was the case at Bechem and Bunso. The higher
yields at Bunso must be due to the more favourable
climatic conditions as well as to the fact that the
oil palm experiments are planted on colluvial
and alluvial soils. Twelve years of continuous
high production in expt 810-1 have apparently
depleted the soil nutrient reserves, as can be
deduced from the leaf analysis data, and responses
to adequate fertilizer applications can be expected
in the years to come.
However, when the land has been cropped
previously, K and P deficiencies soon appear and
Nutrient
status and fertilizer
responses of oil palms in Ghana
economic oil palm yield responses to potash and/or
phosphate fertilizers can be expected even during
the early years of production. The fertilizer trials
at Pretsea and Assin-Foso have demonstrated
this for soils developed over granites. The leaf
analysis data from the farmer's plot near Kusi
and from the sub-spontaneous palms in field K3
of the OPRC indicate that this may also apply to
the soils over Lower Birrimian phyllites. The leaf
samples show only a P deficiency, but the high
production level of good planting material will
probably soon induce a K deficiency unless
potash fertilizers are applied.
The nutrient status of the Forest Oxysols over
granites and Lower Birrimian rocks in the southwestern part of the country is lower as these are
strongly leached. Economic responses to fertilizer
applications, notably phosphate and potash, are
therefore likely to occur soon after planting even
when the area is derived from heavy forest.
From the limited information gathered from
the fertilizer trial at Akaa it would seem that on
Ochrosols developed over Arkosic sandstones in
that area K is the main nutrient requirement for
the oil palm.
The major nutrient requirements for oil palms
on various soils in areas climatically suitable for
oil palm cultivation have thus been assessed to
some extent. However, exact knowledge about
the actual doses of each fertilizer to be applied
to obtain maximum economic responses can only
be derived from more complicated trials, preferably of the 4n design. One such experiment,
comparing N, P, Kat 4 and Mg at 2 levels, was
established at the OPRC in 1969, but more
experiments of this type will have to be laid down
on different types of soil.
In the meantime, recommendations on rates and
frequency of applications are largely based on
experience of other oil palm research institutes in
West Africa (Werkhoven, 1966). The following
remarks may, however, serve as a guidance in
determining an oil palm fertilizer policy in Ghana.
(1) The root system of young palms is not yet
sufficiently developed to exploit a large soil
volume. An annual application of N, P and K is
therefore recommended for a vigorous vegetative
growth during the first 2-3 years after planting
at the following rates (adapted from NIFOR advice).
yrs after
3 planting
Sulphate of
ammonia
0 .250 0·500
1 - kg/palm
Muriate of potash 0·200 0·250 0·500 1 kg/palm
Single
superphosphate 0·200 0·500
1
1 kg/palm
(2) The nutrient status of mature palms depends
on type of soil, climate, previous history of the
land before planting, the level and number of
years of production. Regular foliar diagnosis is
now essential to detect any nutrient deficiencies
sufficiently in time to restore a satisfactory
nutrient status by fertilizer applications.
(3) Nitrogen deficiency is not likely until after
the 12th-15th year of production provided a
leguminous cover crop has been established
immediately after clearing. About 1· 5-2' 0 kg
sulphate of ammonia per palm per year may give
economic yield increases when leaf N is below the
critical level.
(4) Phosphorus deficiency can be expected
sooner or later on most soils in the forest zone.
Annual applications of 2·0-2·5 kg single superphosphate per palm will then be required to
maintain a good level of production.
(5) Potassium. The generally known need for
potash fertilizer applications to maintain high oil
palm yields has been confirmed again by most of
the fertilizer trials in Ghana, although potash
fertilizers may not be needed during the first 10-12
years when the area has been cleared from heavy
forest. Annual application of 1,0-1,5 kg muriate
of potash per palm may be more effective in case
of K deficiency especially on Oxysols, than triennial
applications of higher doses as advised by NIFOR.
In case of a very severe potassium deficiency, an
initial 'shock' application of about 3 kg muriate of
potash may be needed.
(6) Magnesium deficiency may be induced by
potash fertilizer application when the soil Mg
status is already low. When leaf Mg content is
deficient, 2·0-2·5 kg kieserite (or 4-5 Epsom
salts) should be applied per palm biennially
(NIFOR advice).
(7) Time of application. The wet season in the
forest zone of Ghana is characterized by two
distinct rainfall peaks, the first and major one in
June and a second minor peak in October, with a
drier period of :::;;100 mm/month in August. It
would therefore be advisable to apply fertilizers
in August rather than in March, as has been
normal practice, to avoid leaching of the greater
part of the more soluble fertilizers soon after
application due to the heavy rainfall in May-June.
Especially in the south-western part of the country
rainfall can be excessively high in June.
(8) Method of application. Studies on the
horizontal distribution of the root system by
Ruer (1967) confirm that the density of the feeder
roots is highest near the base of the palm. It
decreases rapidly with increasing distance from
the base and becomes very low beyond the leaf
tips. For a maximum uptake of the fertilizers by
the roots it is, therefore, important to broadcast
over the whole surface from near to the base to
under the tips of the leaves. The radius of this
circular surface will increase from 2 m for 2-year
old palms to over 4·5 m for adult palms. Cleanweeding of the ground cover beyond the normally
maintained ring of about 1·5 m radius in mature
plantations prior to fertilizer application is not
recommended.
Acknowledgements
Thanks are due in the first instance to the
Agronomy
Division of NIFOR
(formerly
(WAIFOR) which controlled the six WAIFOR
trials for many years, to the NIFOR Plant
Nutrition Division for analysing the leaf samples
and to the staff of the then Department of Agriculture of Ghana at the various stations who
supervised the establishing of the experiments.
The OPRC is also indebted to the Statistics
Division of the Institute of Horticultural Plant
Breeding at Wageningen for carrying out part
of the statistical analysis of some of the fertilizer
trials. The author is very grateful to Mr A.
Nantwi, who assisted in the leaf sampling in 1969
and also in part of the statistical analysis, and to the
staff of the record section of the OPRC, in particular
Messrs S. W. Ohene- Tutu and C. S. K. Kanda, for
their assistance in compiling the yield records.
To be mentioned as the last, but not the least, are
the field staff at the various agricultural stations
on whom depended the maintenance and yield
recording of the fertilizer trials.
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