Procceding in 31nternational Cocoa Research Conference, COPAL, Lagos, Nigeria 1971 pp.65 -78

RECENT RESULTS OF FERTILIZER EXPERIMENTS ON SHADED CACAO (THEOBROMA CACAO L.) IN GHANA

YAW AHENKORAH AND G. S. AKROFI

Cocoa Research Institute (C.S.I.R.), Tafo, Ghana

SUMMARY

The recent reslllts of factorial fertilizer experiments on shaded cacao (TI/eobroma cacao L.) in both the peasant. the Coco a Researeh Institute, and the Minislry 01' Agricultllre farms in Ghana are presenled and discussed. Phosphorus ís lhe major element 10 which eons;slent responses are obtained. Adose ranging from 40-80 lb P,O,!acre appears desirable. Potas­sium fertilizer is valllable for unshaded high yielding varielies. Interaction effeets of NP, PK and PMg vary from negative to positive, from sile to site and f.om season 10 soason. The economic use offertilizers in cacao clllture presupposes the adherence 10 proper agronomic practices. .

lt is economic to apply fertilizers (triple superphosphale and sulphate of potash or muriate ol' polash) to farms which yield more than 500 lb dry cocoa per aCre (560 kg cocoafha).1t is [urther sLlggested Iha! Ihe "Jire" oflhe cacao farm could be prolonged by applying minimal dose of ferlilizers !o improve the soil produc!ivity.

RÉSULTATS RÉCENTS D'ESSAIS DE FUMURE CHEZ LE CACAOYER (THEOBROMA CACAO L.) Á L'OMBRE AU GHANA

RÉSUMÉ

Les resulta!s recents d'essais factoriels de fumut"e chez le cacaoyer (Tlteobroma cacao L.) a I'ombre sur les établissements paysans, sur CeLL" du Cocoa Research lnstitute et ceux du Ministere de l'Agriculture au Ghana sont discutés. Le phosphre eSI l'élément majeur lequel pour Son! obtenues les réponses consistantes. Une dose d'cntre 45 et 90 kgfha parait etre desirable. La fumLL're potassiqlle esl de valeur pour les varié tes de haute production, cultivés au plein soleil. Les effels des ac!ions réciproques NP, PK el PMg varien! entre négatifs el positifs, de líen el de saison en saison. L'emploi rentable de fumures dans la culture du cacao présuppose J'adhésion au" pratiqlles agronomiques rationeHos.

n es! rentable d'apporter des fllmures (le superphosphale triple el le sulfate ou le chlorure de potasse) aux cacaoyeres qlli produisent plus de 560 kg de cacao sec par ha. 11 est suggéré en outre, que ladurée de la cacaoyere pourrait etre prolongée par l'application de doses minimes de fllmurcs, afin d'améljorer la productivíté dLl sol.

RESULTADOS RECENTES DE EXPERIÉNCIAS COM ADUBOS EM CACAU SOMBREADO (THEOBROMA CACAO L.) EM GHANA

SUMÁRIO

Os autores apresentam e discutem os resultados recentes de el<:periéncias fatoriais com adubos no cacau sombreado (Theobmma cacao L.), tanto em propriedades de camponeses, quanto nas do Instituto de Pesquisas do Cacau e do Ministério da Agricultura cm Ghana. O fósforo é O principal elemento que dá rea~óes regula· res. Adose mais recomendável parece ser de 40 a 80 libras de P20S/acre. O fertilizante de potássio tem valor no caso de variedades nao sombreadas de alto rendimento. Os efeitos da interacao do NP, PK e PMg variam de negativas a positivas, de um local para outro e de uma estacilo do ano para outra. O emprégo economico dos adubos na cultura do caeau exige a obediencia a práticas agronómicas adequadas.

É econí)mico aplicar fertilizantes (superfosfato triplo e sulfato de potássio ou muriato de potássio) a pro­priedades com rendimento superior a 500 libras de cacau seco por acre (560 kg. de cacau/ha). Os autore.s sugerem ainda que a "vida" de uma planta~iio de cacau pode ser prolongada pela aplica~ao de urna dose míni­ma de adubos para melhorara produtividade do solo.

INTRODUCTION

Fertilizer experiments on cacao in Ghana did not begin until the mid-:lifties when control measures against pests and diseases became effective. The earlier work on fertilizer experiments in Ghana has been reviewed by Cunningharn & Arp.old (1962) and the results on sorne of the latest experi­ments at the West African Cocoa Research Institute, now Cocoa Research Institute of Ghana, have

65

been published by Cunuingham & Smith (1961), Cunningham & Arnold (1962), Smith . & Acquaye (1963), Acquay'e & Smith (1965) and Ahenkorah & Akrofi(l967 and 1968), and those by the Cocoa Divis.ion of the Department of Agriculture by Quartey-Papafio & Edwards (1961).

These results have yielded tlle following informa­tion: removal of shade from shaded cacao can result in large increases in yield; both shaded and

unshaded cacao can respond to phosphate fertili­zers; no response was obtained from nitrogen, magnesium, calcium OI micro-nutrient, or from potassium application (except when high yields of unshaded Amazon cacao and response to phosphate created potassium shortage); the depletion in the soil available phosphorus is real with continuous cropping of cacao.

The present paper reports recent results on some of the old factorial experiments and others laid down to investigate the optimum level and fre­quency of fertilizer application to shaded Amazon and Amelonado cacao.

EXPERIMENTAL

Design and layout The designs of the various experiments are

shown in Table 1 including the layout, the levels and types of fertilizers used. A randomised block layout was used in all experiments. For randomly planted cacao on peasant farms which precluded the use of the more orthodox rectangular plots, the circular plot design described by Smith & Acquaye (1963) was used. Adequate guard spaces were allowed between plots and the number of replications was determined by the size of the farm.

Treatments

Fertilizers were hand broadcast in April or May each season and not applied tree by tree, but nitrogen was split applied, one-half in April/May and the second haIr in September. The experiments can be grouped into five, namely:

N x P x K x Mg factorial. These experiments were among the earliest trials, the initial results of which had been reported (Cunningham & Smith, 1961). They included three 24N x P x K x Mg and one 23N x P x K factorial experiments on Amazon cacao plots at Apedwa 1080, Bunso 18c, CRIG G 5 and Bunso 1006 respectively.

22NP factorial. The 22NP x KMgCa factorial experiments on peasant cacao farros at Juaso, Antoakrom, and Mampong reported by Smith & Acquaye (1963) Were modified to 22NP factorial in 1962 after a year's lapse during which no residual effects were obtained.

23 and 32K x Mg factorial. The N x P factorial at Akaa, Biene, K wadaso and Pankese were changed to K x Mg factorial in 1963 with a basal dressing of NP whell lhe results on olher experimcnts on

66

the Institute's station showed that the rate at which K was being applied might be inadequate (Acquaye & Smith, 1965; Acquaye et al. 1965 and Burridge et al. 1964).

Rates of phosphate. The experiment on the rates of application of P was sited on farmer's cacao farrns at Yawnso, Dampon, Mabang and Poano in 1960 in the Ashanti-Ahafo Region. Jt consisted of two levels of P with NKMg basal dressing as indicated in Table 1. The tríals were terminated four years later.

Residual effects of phosphale. In these trials the effect of applying triple superphosphate annually, biennially or triennially over a basal trealmenl of NKMg at four sites-Ahwerewa, Brosankro, Eduam and Hwidiem, on peasant farros in Ashanti-Ahafo Region. was investigated. The NKMg and phos­phate fertilizers were applied together as shown under Table 4.

M aintenance Weeds were kept in check by regular cutlassing

in order to prevent competition for nutrients and moisture. Routine spraying with BHC against capsids was carried out at regular intervals. These sprays were very effective in controlling capsid damage until in 1962 when resistance appeared on the Eduam, Poano and Ahwerewa plots.

RESULTS

The yield data presented here are potential yields estimated from total number ofmature pods on the basis that twelve pods yield one pound of dry cocoa. Where the experiments started when the trees were fully matured and in bearing the yields have been adjusted by an analysis of covariance using the sum of two or three seasons pre-treatment yields as the independent variate.

24NPK Mg and 23NPKfactorial on Amazon cacao The results of the treatment yields for the indivi­dual cropping season (between 1960-61 and 1967-68) for the four sites are shown in Fig. l. Only the main efIects and the highly significant positive inter­actions (P<O.OOI) are shown. Itwasnoted, however that the bulk of the treatments increased yield relative to the control plots. The peak yield for the 1964-65 period is consistent with the national bumper erop obtained during that season.

Table 2 summarises the yield effects of the factorial experiments at the four different sites, over the eight cropping season, and further compares the

o­

--l

TA

BL

E 1

Exp

erim

enta

l des

igns

, fer

fili

zer

type

s an

d le

vels

of a

ppli

cati

on i

n so

rne

fact

oria

l ex

peri

men

ts o

n C

RIG

, C

ocaa

Div

isio

n an

d pe

asan

t far

ros

in G

hana

Sit

e

CR

lG F

arm

C

RIG

(W

AC

RI)

G5

Coc

oa D

iv.

Far

ms

Ape

dwa

Bun

so l

Se

Bun

so 1

006

Ak

aa 3

009

Pan

kes

e 11

16

Bie

ne

Kw

adas

o 40

69

Pea

sanf

farm

s Ju

aso

An

toak

rom

Mam

po

ng

Yaw

nso

Mab

ang

Dam

po

ng

Po

ano

Ahw

erew

a

Bro

sank

ro

Ed

uam

Hw

idie

m

5 3 6 4

10

.5 5 3 4 4 4 4 4 4 4 4 4 4 4 4

Var

iefy

of

caca

o

Am

azon

s pl

ante

d at

8

' X

8'

Am

azon

s' p

lan

ted

al

12' x

12

' A

maz

ons

plan

ted

al

10' X

10

' A

maz

on

, p

lan

ted

al

lO!'

X

lW

Am

azon

s pl

ante

d at

8'

X

8'

Am

elo

nad

o

plan

ted

rand

ornl

y

" ;,

Da

le o

f pla

nlin

g or

age

1954

1953

19

56

1950

1954

1956

1954

1954

Des

ign

2'N

PK

Mg

fac

tori

al

4 re

plic

atio

ns

2'N

PK

fac

tori

al

5 re

plic

atio

ns

3 'K

Mg

X ba

sal

dres

sing

of

NP

unt

il 1

965

whe

n N

was

dr

oppe

d. 1

2 re

plic

atio

ns

5 re

plie

atio

n~'

2'K

Mg

X

basa

l dr

essi

ng a

s A

kaa.

6 r

epli

cati

ons

12 r

cpli

cati

o,;'s

Ove

r 20

yea

rs

2'N

P f

acto

rial

in

195

4 8

repl

icat

ions

" ,. .. ..

8 re

plie

atio

n~'

6 re

plic

atio

n~'

Rat

e o

f p

ho

sph

ate

wit

h N

KM

g a

S ba

sal

7 re

plic

atio

ns

8 replication~'

8 re

plic

atio

n~'

8 re

pli

cati

oru

R

ando

mis

ed.

Ph

osp

hat

e ap

plie

d an

nual

ly,

bien

niat

ly

or

trie

nnia

lly

wit

h N

KM

g

as b

asal

. 8

repl

icat

ions

7 re

plic

atio

n~'

& re

plic

atio

n;'

8 re

plic

atio

n;'

Lev

els

of a

ppli

cati

on

in l

blac

re

N

100

lOO

10

0

100

112

112

100 75

75

P,O

, K

,O

MgO

lO

O

75

50

100

75

50

IDO

50

25

75

50

80

75

25

80

100 40

an

d

80

" 80

"

and

and

lO

O

50

75

25

50

25

50

25

Sou

rce

Ure

a, tr

iple

sup

erph

osph

ate,

su

lpha

te

of

po

tash

an

d

rnag

nesi

um s

ulph

ate

as

abov

e b~t

arnm

oníu

m

sulp

hale

repl

aees

ure

a as

ab

ov

e b

ut n

o rn

agne

sium

su

lpha

te

Ure

a, tr

iple

sup

erph

osph

ate,

po

tass

ium

su

lpha

te

and

m

agne

sium

sul

phat

e

..

Al\

fer

lili

zers

wer

e ap

plie

d in

Ap

ril-

May

eac

h y

ear

bu

l N

ilro

gen

is s

plit

hal

f ap

plie

q in

Ap

ril-

May

an

d t

he r

emai

nder

in

Sep

tem

ber-

Oet

ober

.

-

With Without % With Site Period N N Response P

Bunso 1954-6Ot 1006 6 seasons 972 966 +0.6 998

1960-68 8 seasons 1,216 1,239 -1.9 1,178

Bunso 1 958-6Ot 18e 2 seasons 78 72 +8.3 85

1960-68 .8 seasons 755 781 -3.4 795

Apedwa 1957-6Ot lOSO 3 seasons 794 762 +4.2 8S0

1960-6S* 8 seasons 1,207 1,301 -7.8 \,374

CRIO 1958-60t 05 2 season' 586 562 +4.3 609

1960-68 8,easons 1,327 \,276 +4.0 1,410

Without P

940

1,083

67

740

676

1,134

539

\,202

TABLE

Average yield (lb dry cocoalacre) and percentage'

% With I

Without % With Response K K Response Mg

--

+6.2 995 943 +5.5 -

+8.8 1,244 1,211 +2.7 -

+23.9 79 71 +11.3 72

+7.4 l 739 796 -7.7 776

+30.2'" 774 782 -1.0 820

+21.2'" 1,241 1,267 -2.1 1,309

+13.0' 543 605 -10.2 I 557

+17.3" 1,321 1,282 +3.0 1,289

t The d¡¡ta for the pre-196O sea,ons were after Cunningham & Smith, 1961. '," and ••• ¡¡lean significant at 5%,1 % and 0.1 % level.

68

2

. response of factorial experiments (shaded Amazon)

IWithout % With Without % With Without % With Without % 1 With Without %

Mg Response PK PIe Res- PMg PMg Res- PKMg PKMg Res- KMg KMg Res-ponse ponse ponse ponse

_. ~.

- - - - - - - -

I - - - - - -

I - - 1,337 1,189 +12.4 - - - - - - - - -

78 -7.7 - - - - - - - - - - - -

760 +2.1 365 366 -0.3 385 351 +9.7 372 373 -0.3 362 382 -5.5

736 +11.4 - - - - - - - - - - - -,

1,199 +9.2 1,471 1,251 + 17 .6" l,580 1,229 +28.6*' U95 1,225 +30.2'" 1,410 1,347 +4.7

591 -5.8 - - - I - - - - - - - - -

1,314 -1.9 1,463 1,207 + 21. 2*" 1,407 1,214 + 15.9" 1,479 1,200 +23.3" 1,306 1,285 +1.6

I

69

• .. u -t '-

" O U O

U

>-.. ~

.o ~

~

41

>-

1680

1600

1500

1400

1300

1200

1100

1000

900

700

600

'- / ". . " :

"'-J

i ¡

• " . .

L960/61 61/62 62/63

, . I ~PKMg

\ , \ , \ , \ • \ ,

I :J( \ . \ • o

\

Seasons

t-

NPK

V

t PMg · · • · • • • . . j r i 1/ i JI Ir .. PK .,,1 "

:¡ /.. •

/ /

K o

Fig.l. Shaded Amazon cocoa mean yield (lb dry cocoa/acre) between 1960-68 from NPKMg factorial experiment at Apedwa, Bunso 18e, CR.!. G. G5, and BUfiSO 1006.

70

main effects obtained before the 1960-61 season as reporled al (he 1961 London Cocoa COllference by Cunningham & Smith. The initial response to P at Apedwa and CRIG G 5 still persists. The comparative low yields recorded for the pre-1960 seasons seem more to be a refieclion of the state of maturity of the tree than the initial fertility level of the soils per se. The overall significant positive effect of PK, PMg and PKMg interaction occurred, at least, after three years of continuous fertilizer application.

When the mean yields of individual treatments over the eight-year period, are compared with that of the nil (Table 3), it is found that the bulk of the treatments involving Pare highly significant I (P<O.OOI) with the PKMg, PMg and P treatments topping the list, and having mean yields of 1,213, 1,165 and 1,151 lb dry cocoa/acre respectively. Neither N, K, nor Mg gave significant beneficial effect on these plots. In ract their various combina­tions gave negative effects, with KMg causing a mean dwp of 120 lb dry cocoa/acrejyear over the unfertilized plot.

The seasonal responses to P were consistently high (Table 4) and positive and average 48 % or 650 lb dry cocoafacre!year (range 15-74% or 320-840 lb dry cocoa/acre/year) aboye the minus

P plots. Except for the 1960-61 and 1962-63 periods, seasonal responses to N had all been negative and average 10% los5 (or los5 of·164 lb dry cocoa/acre/year), range 3-21 % (or loss of80-320 lb dry cocoafacrefyear). The net adverse effect ofN on yield was also evident where N was applied together with P, PK or PMg. Response to K alone by the shaded Amazon had not been cOTIsistent in -lhe sense that both high negative and high positive responses were recorded fol' different cropping seasons.

Response to rates of NPKMg at peasant and Cocoa Division farms

Following the response to NPKMg and NP fertilizers reported' by Cunningham & Lamb (1959), Cunningham & Arnold (1962), Smith & Acquaye (1963) factorial experiments were laid down to test separately the effect of the various eIements. Results of the responses to rates of N and P at the fanuel's' fanus and to K and Mg at Cocoa Stations are summarised in Table 5. The experi­ments sited on fanuers' fanus were discontinued after the 1964-65 season leaving those at the Minis­tey of Agriculture Cocoa Stations. The response to N is again general1y negative. The application of

TABLE 3

Comparison of fhe eflecl of Ihe various trealmellts relative to the ni! for ¡he 8-year (1960-61-1967-68) season

• Number in brackels represenls mean yieJd (lb dry cocoajacre) of respective Ircalmen!.

71

TABLE 4

Seasonal responses to N, P, K, Mg [ertilizer in [actorial experiments (/our sites)*

____________ 11960-61 11961-6211962-6311963-641_1~9_64--_6_5_1_1_96_5_-_66_ 1966-67

Responses to N (lb per acre) I +65 -129 I +94 I -110 -196 -87 -141

1967-68

-322 % Response +1.4 -21.5 +6.7

1

-6.2 -12.8 -9.7 -3.2 No. of responsive sites O O O O O O O -------------------I------~------Responses lo P (lb per acre) +325 I +555 I +597 I +836 +675 +941 +502 +752

-6.1 O

% Respome +34.0 +64.2 +47.8 +74.1 +47.6 +93.0 +11.9 +14.9 No. of Responsive sites 1 2 3 3 2 4 2 3

------l----I---I-----Ii----il----I--~¡-----I----Responses lo K (lb per acre) -68 +47 l' -140 I -343 -23 +154 I +306 +120

N% ResfPonse . . -5.8 +1.2 -22.0 -32.8 -01. 0 1 +1

0°.7 +4.8 +1.6

o. o Responslve sites O O 2 O O 1

+ 105 + 103 ' +96 I +99 1--,--, -IZ-9--I--+-S-3--!I-+--1-69--I----II-S--Responses to Mg (lb per acre) % Response' No. of Responsive sites

+209 +15.2 +12.2

1

+4.6 +6.S +5.4 I +03.2 -1.7 O I

I O 1 O I O O O

. I

" Three sités received N, P, K and Mg and one N, P and K trealments. See Table 6 (a).

80 lb P.Os!acre appears to give a comparatively higher response than half this dose but there is, however, no significant difference between the yield response to both leve/s. AIso, significant response to either or both level, differs from site to site and from season to season. On the shaded Amazons the average response to the first Ievel of either K or Mg is comparative1y larger than their corres­ponding second levels. Averaged over thefive-year period the mean difference between the response to K, and K 2 is 95 lb dry cocoa/acre andthat of Mg, and Mg. is 33 lb dry cocoa/acre.

Residual effect o[ P

The data in Table 6 show that of the fOllr sites, Ahwerewa and Brosankro are the only ones where responses to phosphate were obtail1ed. It will be seen that at Ahwerewa significant responses were obtained each season when phosphate was applied at 80 lb P 20ó/acre annuaJIy except in 1963-64 and 1964-65. However, consistent annLlal responses were. obtained on the plots where the same level of application was made triennially. These residual effects were not supported by yields on the plots which received the same dose for the biennial application; on the latter plots significant response was only obtained in the season in which applica­tion was made. There were no significant responses in the first two seasons at Brosankro. In the third year when yield began to decline on this fann, howeverl significant responses were obtained to the annual and biennial applications made in that season. Considering Ahwerewa, Bronsankro and

72

Eduam. where response to P application had beea positive, it set'l1IS that it is beneficiaI to apply the phosphate triennially on these plots.

lnteraction effects

The seasonal effects of NP, PK and PMg in ter­actions are reported in Table 7. There are indica­tions on some sites (Apedwa, CRIG a5 and Mampong) that where significant responses were obtained to P, N fertilizer tended to reduce the effect whereas at Bunso 1006 and Bunso 1Sc, the N fertilizer gene rally tended to inerease the response to P. At Apedwa 1080 and Mampong this negative NP interaction was significant in most of the seasons. A consistent positive PK interaction effect occurred at Bunso 1006 over the eight seasons. Nonetheless, except for the 1966-67 season, the effect of PK on yield at either Apedwa 1080 or CRIG G 5 was negative with the buIk being highly significant (P<O.01). Even though at Bunso 1Sc, where for the past ten years, no significant response to any of the treatments has been recorded, the additíon of Mg tends to ¡nerease yield over the P-treatment. The latter has be en found to be gene­rally beneficia!. Similar positive PMg response has been obtained at Apedwa. However, at CRIG G5 the PMg interaction has been negative except for the 1960-61 and 1961-62 seasons.

D1SCUSSION

Main effects

The results of the fertilizer experiments have confinned previous studies that phosphorus is

-..¡

w

TA

BL

E 5

Seas

onal

res

pons

e to

rat

es o

f N,

P,

K a

nd M

g f

erti

lize

rs e

xper

imen

ts (

lb

dry

coco

a pe

r ac

re)

at f

arm

ers'

far

ms

and

Coc

oa

Div

isio

ns

1967

-68

1196

0-61

\

1961

-62

1 19

62-6

3 i

1963

-64

1 19

64--

65

1 19

65-6

6 11

966-

67

I

1---"--------------

------'-

---

Res

pons

e to

N

% R

espo

nse

No.

of

site

s w

ith

sign

ific

ant

resp

onse

Res

pons

e to

Pl

% R

espo

nse

No.

of

si te

s w

ith

sign

ific

ant

resp

onse

Res

pons

e to

P2

% R

espo

nse

No.

of

site

s w

ith s

igni

fica

nt r

espo

nse

Res

pons

e to

Kl

% R

espo

nse

No.

of

site

s w

ith

sign

ific

ant

resp

onse

Res

pons

e to

K

---

-481

-4

.9

O

72

I 116.7

I

35

I 5"

7 I I

1 I ;

At

Yaw

nso,

Dam

pong

, M

aban

g an

d P

oano

(fa

rmer

s' f

arm

s)

136

I -5

16

-204

56

0

.7

i -4

.1

O

I O

!

-4.3

5

.9

O

O

----

17&

72

11

2 16

3 31

.9

12.0

"1

8.1

24.5

O

1

J 1

196

117

175

112

35.2

19

.6

28

.2

16.8

1

2 2

1

At

Bie

ni,

Aka

a, K

wad

aso

and

Pan

kese

(C

ocoa

Sta

tion

s)

103 5

.2

1 6

327 11

. 4

1

189

635 41

.4

1

,1 27

2 5.0

1

,t,.

"lV

,t

,,,L

. 28

2 23

0 .2

2

1.7

15

.9

,h s

igni

fica

nt r

espo

nse

O

1

Res

pons

e to

Mg l

90

11

3 16

6 90

%

Res

pons

e 2.

O

2. 6

7

. 2

1. 7

N

o. o

f si

res

wit

h si

gnif

ican

t re

spon

se

O

O

O

O

83 2.5

O

251

Res

pons

e to

M2

41

143

42

53

102

% R

espo

nse

1. 7

6.

2

3 . 7

, 3

. O

4.6

N

o. o

f si

res

wit

h si

gnif

ican

t re

spon

se

" O

O

O

0

"1

" __

~

P,

=

40 l

b P

,O,f

acre

, K

, =

75

lb K

,Ofa

cre,

Mg

, =

25

lb M

gOfa

cre.

p

. =

80

lb.

P,O

,fac

re,

K =

100

lb

K,O

facr

e, M

g.

= 5

0 lb

MgO

facr

e.

TABLE 6

Ca) Residual effect of phosphate fertilizer al four sites (Yield in lb dry cocoa per acre)

Seasonal Yield Site Treatment t -

I

.- ._~

1960-61 1961~62 1962-63 I

1963-64 1964-65 -------

I Nil 392 399 467 508 I

692 Ahwcrcwa Pa 535* 576(*) 724** i 649 790

Pb 445 560(*) 585 660 919 Pt 594* 706*(*) 611* 792* 991*

S.E. ±132 ±159 ±131 ±IS4 ±206 ---------

Nil 976 1,089 506 402 1,037

I Pa 1,164 1,352 637(*) 683* 1,148

Brosankro Pb 926 1,352 , 678* 517 1,153

I Pt 1,057 1,370 497 638* 1,096

I S.E. I ±259 ±329 ±154 ±154 ±222

Nil I

751 824 792 758 I 626 Pa 776 985 826 826 672

Eduam Pb 776 858 687 734 613 Pt 1,005 1,143 1,000 746 776

S.E. ±331 ±286 ±352 ±243 ±293 I

Nil 1,566 1.150 1,221 833 1,831 Pa 1,550 1,025 1,119 703 1,749

Hwidiem Pb 1,522 1,275 1,155 839 1,734 Pt 1,477 1,121 1,048 724 1,672

I S.E.

I ±256 ±218 ±254 ±156

I ±322

(b) Seasonal mean response lo residual effect of phosphate fertilizer al Ahwerewa, Brosankro and Eduam

Response to Pa 356 I 601 422 % Response over Nil 16.8 26.0 23.9 No. of Sites 3 (1) 3 (1) 3 (2) --Response to Pb 28 458 177 % Response over Nil 1.3 19.8 10.0 No. of Si tes 3 (O) 3 (l) 3 (1) --Response to Pt 537 907 325 % Response over NiI 25.3 39.2 18.4 No. of Si tes

I 3 (1) 3 (1) 3 1)

t Annual applications (Pa) were made in aH seasons. Bienníal applícatíons (Pb) were made in 1960-61, 1962-63 and 1964-65 seasons. Triennial applications (PI) were made in 1960-61 and 1963-64 seaSOns. No. of signifIcant responsive sites in brackels. • and ., .• mean significan! at 5 % and 1 % level.

74

.~

I 531 I 255

1

31. 8 10.8 3 (1) 3 (O)

243 330 14.6 14.0 3 (O) 3 (1)

508 50S 30.5 21.6 3 (2) 3 (1)

TABLE 7

Effects 01 NP, PK and PMg interaction on yield 01 shaded cacao

I Season

Si te Factor I

..

I

! I

I 196Q....6 l i 1961-62

I 1962-63 1963-64 L 1964-65 ! 1965-66 I 1966-67 1967-68

-- I

I ,

Apedwa 1080 NP , •• _.

-' •• I

-* ! -

! - - - -

CRIG as + - -** - I - - •• -

I

-*** " Bunso 1006 i " - + + + - + I + +

Bunso lSc + + + + - + I + + " I I Juaso "

- - - ! - +

I Antoakrom

" + + - - -Mampong - • -• _.

- * -"

Apedwa 1080 PK _ .. - •• -" -* - - + I

-" CRIG G5 - - -" -**. - • •• - +* -

" Bunso 1006 " -1- -1- , -1-"

I -1- -1-* +* -1- -1-*

Bunso 18e " + -1-

I - -

I

- l. + -I

-

Apedwa 1080 PMg I

I +' I -1- + -1-" + -1- -

1

-CRIG G5

1

-1-

1

+" I

_ .. -" I

- •• -• - • • - " " I I Bunso 18e " -1- + -1- I + - +

I

-1- I + I

Sign (-1- or - ) indicates whelher or nol interaction effect is negative or positive . • ," and ••• indicate P<0.05, 0.01 and 0.001 respectively.

the major element to whi6h responses are obtained. However, responses have not always been obtained on the same soil from season to season. This suggests that there may be a residual effect which makes annual application unnecessary; but this has not been completely substantiated by the results of the experiments to test the residual effects of phosphate application (Table 4).

The results a150 show that on some soils the effect of applying 40 lb P 20S/acre was not different from the application of twice that amount. On the other hand ~t Poano significant increase in yield Was obtained from the application of the higher rate and not to the first rateo It is therefore sug­gestive that higher levels of P application may be necessary on the Poano plot, and it is possible that on other plots where no significant responses have been obtained the rate of 80 lb P205!acre might be too low. The latter assertion is consistent with the faet that most of these soils are known to have high phosphorus retention capacities (Ahen­korah, 1967).

Of the eigh t sites where K fertilizer was applied only on Kwadaso plot was response obtained; at CRIG G5, Bunso ISe and Apedwa 1080 non­significant depression of yields resulted from potassium application. Since the K deflciency on Amazon eocoa was reported (Acquaye et. al., 1965) field observations have indicated that potassium deficiency symptoms occur on several farms grow­ing the Amazon varieties. It has been observed that the prevalence is eommon particularly on

75

unshaded or very thinly shaded Amazon cacao; conversely potassium response is positive and increases with decreasing overhead shade. In most cases where Amelonado and Amazon varieties are growing side by side on the same soil type, if there should be any potassium deficiency, it almost invariably shows up first on the latter variety. This is probably because the Amazons come into bearíng earlier and by their heavier yields have higher K requirements. The published results (Ahenkorah & Akrofi, 1967) of the Amazon shade and manurial experiment (K2-01) at Tafo support the aboye observations.

There was no response to either nitrogen or magnesium except on Apedwa 1080, where mag­nesium gave increased yields in 1958-59and 1962-63 seasons. With nitrogen, the work by Acquaye (1968) on the nitrogen transfonnation in soil under cacao appears to suggest that the time of application is not appropriate. At the beginning of the rain s (April-May) after the long dry period which .extends from November. through March,.there is a flush ofmicrobial activity accompanied by a considerable amount of mineralization of the heavy liuer. It may therefore not be opportune to apply nitrogen fertilizers at this time. To this end, new tríals have been designed to test the time and split application of nitro gen.

In the recent progress report on cacao-fertilizer trials in Western Nigeria, Wessel (1968) obtained not only a positive linear effect from the application of urea over a five-year (1962-67) period but al so

over the eight different sites, he reported abou t 50 per cent yield increase from the interaction effect of (NaPl or N 3P2) urea (261 lb urea/acre) and triple superphosphate (eíther 134 lb Of 201 lb triple superphosphate per acre).

Of late, deficiency pro blems of boron (Asomaning & Kwakwa, 1967) and zinc (Ahenkorah, 1969) have been noted with the Amazon variety in the field. It may soon necessitate our including micronu-. trients in factorial tríals.

The economic yield leve!

There is a clear indication that response to fertilizers by mature cacao vary from site to site and sometimes from season to season. Considering on1y the positive responses on farmers' Amelonado cacao, the overall percentage mean increase in yield due to fertilizers is about 30 % (range 16-53%). In Table 8 the current local price ofthis 30% increase yield (due to fertilizer) is compared with the present cost of fertilizers applied peracre. The gross profit or 1085 column of the table excludes the transport and handling charges and the cost of labour in applying the fertilizer and harvesting the increased yield.

It will be seen from Table 8 that it is economic to apply fertilizers to most farms whose initíal yield is more than 500 lb dry cocoa/acre (560 kg dry cocoafha). At the current local price of Nj28.00 per 60 lb dry cocoa, the gross profit margin increases from Nj25.06 to Nj211.94 (US. $4.96-11.70) per acre, if only phosphorus and potassium fertilizers are used. Not much is gained when the initia\ yield, i.e. without fertilizers, is less than 500 lb dry cocoa/acre (560 kgfha). Therefore, with the national average yield ranging from 250-350 lb dry cocoa/ acre the bulk of our peasant farmers will be worse off if they use fertilizers under present farro practices.

However, this low national· yield can easily be increased beyond the 500 lb limit if the basic proper agronomie practices, such as effective control of pests and diseases, regular and thorough brushing of weeds to avoid competition for nu­trients and available moisture and harvesting at proper time, are adhered too At Tafo the application of these basic cultural practices on shaded Amelo­nado cacao without the use of fertilizers (Kl) have caused an average yield of more than 900 lb dry cocoa/acre (range ó75-1183 lb dry cocoa) for the past nine years. There is therefore no techni­cal reason why the current national low yield/acre canoot be considerably increased to permit the economic use of fertilizers.

76

•

Soil productivity

It is important to eonsider fertilizer use from another view point. Each year owing to the removal of pods and beans the soils cropped to cacao lose sorne essential minerals. In terms of nutrients this loss is estimated, from an average annua! market­able harvest of 400,000 tons dry cocoa beans (plus testa), to be 16,000 tons NPK, i.e. about 4 % per year of the exported beans consists of NPK, nu­trient which is not returned to the soiL The loss is considerably higher (39,700 tons NPK per year) when the analysis of the husk is incIuded. The latter, however, is generally Ieft at the pod break­ing points on the farms.

As cropping gets oIder, the accumulated loss of nutrients ¡ncreases and henee the older farms are most likely to be marginal for one or more plant nutrient requirements. Once this state is reached, the trees suffer under any stress, lose vigour and regenerative power and hence become susceptible to insect (thrips, capsid) damage and eventual death.

Ahenkorah & Akrofi (1967) showed that a definite depletion in soil available phosphorus occurred after ten years of continuous cropping of Amelonado on a plot at Tafo. They further sugges­ted the existence of a probable relationship between the condition of the tree and its 5usceptibility to insect attack. In short, the absence of essential plant nutrient might be one of the major under­lying causes of 108s of cacao farros; thus the use of fertilizer is first and foremost for keeping the farm as a producing entity, and also foc increasing yie1d per unit arca. A minimal dose of fertilizer might improve the productívity of the soil, ¡.e. prolong the "Jife" of the farm, but not necessarily giving an economic return in terms of money. It is equally just possible that improving tlle soil fertility status and ipso Jacto the plant food status will enable the trees to withstand inseet attack and thus obviate the need for frequent spraying. This can a1so be useful in subsequent rehabilitation effort.

SlJMMARY AND CONCLUS10N

(1) Phosphorus is the majar element to whieh responses from. mature cacao are obtained and there is a suggestion of residual effect from phosphorus fertilizers.

(2) A range of 4Q-80 lb P 2051acre in the level of application seems desirable but it appears that a bigger dose may give a higher leve! of ~¡gnificance for many sites.

(3) Demand for potassium is not very critical

•

Fertilizer

Triple superphosphate K2S04,

Urea

(NH4hS04 Single P KCl**

1 b dry cocoa per acre without fertilizer

250 350 500 600 800

1,000

I

TABLE 8

The economics of fertilizer use far dijferent yield/acre

I

Costfton* I

:f:28 E23

E29

E2l f16 E18

I

% Conc·fton Rate/acre

45% P205 1,008.00 p 20. 80 lb P2 0 6 48% K20 1,075.20 K20 50 lb K 20

46% N 1,030.40 N 100 lb N

I

I I

I I I

20% N 448.00 N 100 lb N I 18 % P205 403.20 PP5 80 lb P2O. 60% K20 1,344.00 K20 501b K20 I

i i

[ I I

Cost per acre

f2.22 or N~5.44 EI.07 or N~2.62

f.3.29 or N~8. 06

:f:2.S1 or N~6. 88

E6.1O OI N~14.94

E4.69 or N~11.49 fJ.17 or N~ 7.77 fO.67 or N~ 1.64

---E8.53 or N~20.90

Yield/Acre Current local prjce at

30 % increase due to N ~8 .00 per load of Gcoss profit with*** fertilizer use I

60 lb dry cocoa Triple super P and K2SO.

I lb dry coco a I N~

I I I ,

75 I 10.00 f 0.79 OI + N~ 1.94 105 I 14.00 E 2.42 or + N~ 5.94 150 20.00 E 4.87 OI + N~11.94 180 24.00 :E 6.50 or + N~15.94 240 32.00 :E 9.77 OI + N~23.94 300 40.00 ;[13.03 oc + N~31.94

• tl Njl = USo $0.98 = toA08 sterling.) •• KCI is hygroscopie; Critical RH at 84QP .

••• ExcJuding transport, handling charges and labo L1r cast in applying fertilizer and harvesting the inerease.

77

except for unshaded or thinly shaded Amazon and the high yielding varieties.

(4) The interaction effect of NP is generally negative and more work is needed to finally deter­mine the conditions under which N could be profilably applied or eliminated. Similarly the effects of PK, and PMg interactions on yield depend on individual site and seawn.

(5) The economic use of fertilizers in cacao culture has as, ils essential pre~requisite, the slriet adherence to proper agronomic practices.

(6) For a local sales price of cocoa not less than N!Z6.50 per load of 60 lb and at the current fertilizer cost, il is economic to apply fertilizer to cacao farms which yield more than 500 lb dry cocoa per acre (560 kg!ha).

(7) To improve the productivity of the soils and hence prolong the "Jife" of cacao farms a mínimal dose of fertilizers may be necessary.

ACKNOWLEDGEMENT

The aulhors are grateful to Messrs. R. K. Cunningham, R. W. Smith and Dr. D. K. Acquaye, former CRIG employees, for their cOl1tribution in the initial phase of these trials and are indebted to both the fie1d staff of CRIG Chemistry Division and the officers of the Ministry of Agriculture, Cocoa Division for their technical assistance.

Published with the approval of the Director, Cocoa Research Institute of Ghana.

REFERENCES

Acqcaye, D. K. (1968). Nitrogen transCormation in soi, under cocoa. Rep. Cocoa Res. Inst., Ghana, 1965-66 133.

Acquaye, D. K. & Smith, R. W. (1965). Effects oC ground covers and fertilizers on establishment and yield of cocoa on clear-feUed land in Ghana. Exp. Agrie. 1, 131-139.

Acquaye, D. K., Smith, R. W. & Lockard, R. G. (1965). Potassium deficiency in unshaded Amazon COcoa (Theobroma eocao L.) in Ghana. J. hort. Se;. 40, 100-108.

Ahenkorah, Y. (1967). Phosphorus . etention capacities of some cocoa growing soils of Ghana and ¡heir relationship with soil properties. Soil sci. 105, 24-30.

Ahenkorah, Y. (1969). A note on zinc deficiency in cacao (Theobroma cacao L.). Ghana Inl. agríe. Sei. 2, 3-6.

Ahenkorah, Y. & Akrofi, G. S. (1969). The status ofan Amelonado shade and manurial experiment (KI) at Tafo. 2nd Int. Cocoa Res. Conj. Salvador, 1967, 325-329.

Ahenkorah, Y. & Akrofi, G. S. (1968). Amazon cacao (Theobromp cacao L.) shade and manuria! experiment (K2-01) at the Cocoa Research Institute ofGhana. 1: First five years. Agron. J. 60, 591-594.

Asomaning, E. J. A. & Kwakwa, R. S. (1967). A note on boroa deficiency and fruit malformations in cocoa (Theobroma cacao L ). Ghana l. Sei. 7, 126-129

Burridge, J. c., Lockard, R. G. & Acquaye, D. K. (1964). The levels ofnitrogen, phosphorus, potassium, calcium and magnesium in the leaves ofcacao (T/¡eo~ broma cacao L.) as affected by shade,fertilizer, irrigation and season. Afln. Bol. N.S. 28,401-417.

Cunningham, R. K. & Arnold, P. W. (1962). The shade and fertilizer req uirements of cacao (Theobroma cacao L.) in Ghana. J. Seí. Fd. Agríe. 13, 213-221.

Cunningham, R. K. & Lamb, J. (1959). A cocoa shade and manurial experiment at ¡he West African Cocoa Research Institute, Ghana. 1: First year. J. hort. Sci.34, 14-22.

78

Cunningham, R. K. & Smith, R. W. (1961). The significance of sorne recent work in Ghana on shade and nutrient requirements of cocoa. Rep. Proc. Cocoa Con! 1961, 119-122.

Quartey~Papafio, E. & Edwards, D. F. (1961). The use oC fertilizers on cocoa in Ghana. Rep. Pro~. Cocoa Conj 1961, 123-125.

Smith, R. W. & Acquaye, D. K. (1963). Fertilizer responses on peasant cocoa farms in Gbana: a factorial experimento Emp. l. exp. Agric. 31,115-123.

Wessel, M. (1968). 2nd Progress Report 011 G.R.I.N.­M.A.N.R. fertilizer tria/s.