MARDI Rel Bull. 5, I: (6 - 22)

YIELD RESPONSE OF OIL PALM TO FERTILIZERS INWEST MALAYSIA

I I . INFLUENCE OF SOIL AND CLIMATIC FACTORS

H.L. FOSTER and GOFI HOCK SWEE

Accepted for publication on 8 June, 1976

RJNGKASAN

Setelah membuat pemilihan ke atas kajian-kajian baja kelapa sawit yang telah dijalankan diMalaysia Barat, gerakbalas hasil buah sawit basah terhadap baja-baja N, P dan K, padakadar-kadar kegunaan baja lain yang optima, setelah pelarasan dibuat kepada kadar hasil danfaktor sawit, telahpun dapat dikaitkan kepada faktor-faktor tanah dan cuaca. Dalampercubaan-percubaan di tanah pesisir, gerakbalas purata N dan P adalah mempunyai kaitan yangpositif dengan jumlah hujan tahunan. Di percubaan-percubaan tanah ulu (inland soils) gerakbalasN dan K pada tiap-tiap tahun adalah mempunyai kaitan yang negatif kepada kekuatan larut lesapdan kekerapan penaburan baja, manakala gerakbalas purata K pada beberapa tahun adalahmempunyai kaitan yang positif kepada pH tanah dan negatif kdpada kandungan tanah liat. Paclatanah ulu, gerakbalas purata P adalah mempunyai kaitan yang positif kepada pH tanah.

INTRODUCTION

In a previous paper (FosTER, 1976) yield response functions, calculated from fresh fruitbunch yield data accumulated over pedods of 4-5 years, were presented for twenty selected oilpalm fertilizer trials. Response to individual fertilizers was found to be very dependent on thelevels of other fertilizers. The responses to individual fertilizers in each trial were thencalculated at optimal (or non-limiting) levels of other fertilizers. When the trials on coastal andinland soils were considered separately, these responses were found to be all higlily significantlyinversely related to yield level, and in some cases were aiso related to palm age or density. Inthis paper, individual responses to N, P and K fertiiizer at optimal levels of other fertilizers,after correction for yield level and palm factors, are further considered in relation to soil andclimatic factors. (There were too few responses to Mg fertilizer to allow any usefulcomDarisons).

METHODS

The site of each trial was first surveyed, after which inspection pits were dug in thecentre of palm avenues in representative areas. Details of the soil profiles revealed in these pitswere recorded and soil samples were coilected from the different horizons. In addition,composite 0-30 cm soil samples were collected from all plots of all trials still in progress.

The soil samples were analysed for organic carbon by the Walkley-Black method and fortotal nitrogen by the Kjeldahl procedure. Particle size distribution according to the Atterbergscale was determined by a standard pipette method (involving destruction of organic matter an'ddispersion with sodium hydroxide) and by the rapid Bouyoucos hydrometer method (notinvolving organic matter destruction but also using sodium hydroxide as dispersant). Soil pHwas determined at a soil/water ratio of 112.5 by glass electrode. Bases were extracted byshaking 29 soil with 100 mi neutral normal ammonium aaetale ovemight, and after individual

determination of calcium, magnesium, potassium and sodium, total extractable bases (TEB) was

calculated by summation. Aluminium and hydrogen were extracted by rapid leaching of 29 soil

with 100 ml of normal sodium chloride. and tire sum of these two cations is taken to be total

extractable acidity (TEA). The sum of TEB and TEA indicates the level of total extractable

cations (TEC) at the natural soil pH.

Equilibrium moisture content was determined in pressure plate apparatus, at 1/10 bar onthe soil samples in their relatively undisturbed field state, and at 15 bar on the same samplesafter they had been dried, ground and sieved. The differen0e betrveen these two measurementswas taken as the avaiiable water holding capacity (AWHC) of the soils. Percentage availablewater in the top 90 cm of soil and water loss due to percolation beyond a depth of 90 cm (or

due to run-off) was estimated for each day of each trial from the AWHC measurements anddaily rainfall and evapotranspiration data. These estimates are rather crude sinceevapotranspiration from the soil/palm system over the entire range of percentage available soiiwater was assumed to be equivalent to evaporation from an open water surface, and no accountwas taken of the water table in coastal areas. However measurements which would have allowedmore accurate calculations are not available.

RESULTS

Variation in response to individual fertilizers

Average F.F.B. yield responses to individual ferti l izers over a period of 4-5 years, atoptimal levels of other fertilizers and at specific yield levels, have been calculated for each trialfrom the response functions determined' by FOSTER (1976), and are shown in Table I.Although it is possible to predict response at any yield level from the response functions, onlyresponses at yield levels actually obtained in the trials are shown in Tsble l. It is clear thateven at non-limiting leveis of other fertilizers and at a fixed yield leve1, there is stillconsiderable variation in yield response to individual fertilizers. Thus for example at an annualyield level of 26 rlha F.F.B., response to lkg/palm suiphate of ammonia ranges from 0.7 to 1.2t/ha on coastal soils and from 1.3 to 2.1 t/ha on inland soils, whilst response to 1 kg/palmmuriate of potash ranges from 0.4 to 0.9 t/ha on coastal soils and from 1.3 to 1.7 tiha oninland soils. F.F.B. yield responses to N and K fertilizers, at optimal levels of other fertilizersand at specific yield levels, and results for selected coastal and inland trials are shown in Tables2 and 3 respectively. It can be seen that in individual trials. at a fixed yield level, there isconsiderable variation in response from year to year.

Soil Survey

A summary of the soils identified at each site is given in Table 4. Trial l0 on Selangorseries soil had an acid-sulphate layer at 75 cm and the water rable was maintained at least atthis level to prevent the development of extreme acidity which occurs on oxidation. The watertable in many of the trials on coastal alluvial soils was high; mottling was observed at a depth

of 30 cm in trials 2,5,6 and 7 and at a depth of 60 cm in trial 1. Many of the inland soilscontained some laterite but only in trials 22 and 4l was it extensive at a shallow depth. Intrial 9 the average depth of the peat was approximately one metre.

Soil Analyses

Average soil analysis results for the top 30 cm of each trial are presented in Tables 5 and6. As would be expected, the silt and clay levels estimated by the hydrometer method are

N Response P Response K Response

Yield 28./-o1 . 422 ^1-O'\ ll22 28 22 24 26 28

CoastalTrial

I

3

5'l

Inland Trial

9

A

6 l

1 0

2

6

2 7

2 I

26

/.)

28

Z J

1 A

4 1

22

8

0 . 1

] . I

r.2 l .0| .1.

_ 0 .1

1 . 5 1 . 0

1 . 7 1 l

1 . 0

1 Al . a

2 . 0

0 . 1

0 .8

0 .3

0 .4

0.4

0 . 5

/ . .J

2 . 1

2 . 5

1 . 4

0 .8

l . t i

2 . 0 r . 7

1 . 8 1 . 4

0 .3 *

1 a

0 . 5 1 . 3

2 . 1

0 .9

t . 6 1 . 2

0 .3

0.9

0 . 5

0 .6

0.4 0.3

1 . 6 l . J

u. )1 1

0.3

1 . 2

0 .8l 1t . l

2 . 1 1 . 4 0 . 7

4 .6 3 .0

5 . 1

1 . 8 2 . 0

1 . 0

0 . 8 0 . 1

0 .6

0 .9

0 .4 0 .3

l . t

0 .6

0 .5

2 . 2 1 . 9 1 . 7 1 . 3

2 .8

2 . 2 1 . 9 1 . 5 0 . 8

1 . 8

u . l

2 . 7 1 . 9

1 . 4 1 . 3 1 . 11 ' l

TABLE 1. PREDICTED AVERAGE YIELD RESPONSE TO INDIVIDUAL FERTILIZERSOVER 4 -5 YEARS, AT OPTIMAL LEVELS OF OTHER FERTILIZERS AND AT SPECIFIC

YIELD LEVELS (IN T/HA/YR F.F.B. PER KG FERTILIZER PER PALM PER YEAR).

i Average over selected 5 year period. Over only the last 3 years of this period tlre average was 0.6.N l'ertilizer = Sulphate of ammoniaP fertilizer = Christmas Island Rock PhosphateK fer t i l izer = Mur iate of Potash.

TABLE 2. PREDICTED YIELD RESPONSE TO N AND K FERTILIZERS, ATOPTIMAL LEVELS OF OTHER FERTILIZERS AND AT SPECIFIC YIELD LEVEIS,

IN INDIVIDUAL YEARS OF SELECTED TRIAIS ON COASTAL SOII'S (IN T/HA/YRF.F.B. PER KG FERTILIZER PER PALM PER YEAR) AND CORRESPONDING* RAINFALL

AND SOIL AVAILABLE WATER DATE

TrialYear afterPlanting N Response K Response

Rainfallcm/yr

AW%

1 lt213

Y = 2 5 Y = 2 6

1 . 3 8 1 . 2 0

r .34 -1 .42

-1."72 - 1 .50

Y = 2 5 Y = 2 7

0.88 0.s4

1.08 1 .03

1 . 3 7 t . t 1-0.s4 0.42

1 . 9 7 1 . 6 3

Y = 2 4 Y = 2 5

1.59 t .44

t . 4 t 1 . 3 1

r .27 1 .23

226

213

1 5 1

200

1 9 5

2 2 1

214

231

204

151

204

_t )Ll

221' t 1 A

1 7 7

46

39

J Z

48

z+

46

80

60

60

52

8

9

t 0

1 1

t 2

46

4 l

47

45

44

Y = 2 6 Y = 2 7-0.40 -0.02

034 0.34-o.43 1.35

1 . 2 9 1 . 1 1_ 1 . 3 1 _ 1 1 8

Y = 2 2 Y = 2 3-0 .68 0 .s6

0.93 -1 .06

0.59 -0 .15

-0.60 -0.40

-1.57 | .45

1.08 0 .75-0.24 -0.2s

7

8o

1 0

1 l

1 2

l 3

Y = 2 0

4 . 1 4

1 . s 6

0.34

1.47

2 . 1 6

0.99

0.77

Y = 2 2

1 . 8 7

z - z J

r .02

1 . 3 7

1 . 9 1

0.7 5

0 . 7 3 '

N fertilizer Nitro 26, but above responses have been adjusted so that they are to an equivalent amountof Sulphate ammonia.

K fertilizer Mudate of potash.xRainfall and available water in 0.90 cm soil were determined over a l2-month period commencing 7 months

before the year in which yield response was recorded.

TABLE 3. PREDICTED YIELD RESPONSE TO N AND K FERTILIZERS, ATOPTIMAL LEVELS OF OTHER FERTILIZERS AND AT SPECIFIC YIELD LEVELS,

IN INDIVIDUAL YEARS OF SELECTED TRIALS ON INLAND SOILS (IN T/HA/YR. F.F.B. PER KG FERTILIZER PER PALM PER YEAR) AND CORRESPONDING*

LEACHING SCORES AND FREQUENCIES OF FERTILIZER APPLICATIONS.

TrialYear afterPlanting N Response K Response

leachins Ferti i izer

score Applicationsper year

o

7

8

9

l )

t 6t 7l 8

Y = 2 8 Y = 3 2

1 . 7 2 | . 6 2

0.51 0 .39

4.2s 2 .88

2.28 1 .39

Y = 3 0 Y = 3 2

3.11 3 .20

0.8s 032

2.80 2 .21

r .2 '7 l . s2

A-

J

1

4

0

2

I

0

1

2

I

I

2

J

A

t >

zo

Y = 1 2

4.45

2.57

+ . J J

3.73

Y = 1 9A 1 A

1 . 8 0

4.33

J . + |

Y = 2 4 Y = 2 7

| .7 6 0.99

1 .7 5 1.44

1 . s 8 0 . 5 5

1 . 8 4 1 . 2 1

2.00 0.86

Y = 2 1 Y = 2 2

2.52 2.46

2.06 2.28

1.68 1 .49

1 . 5 5 1 . 9 1

Y = 1 7

4.45

u- ) /

4.69

4.66

Y = 2 4

1 . 5 2

1 . 7 s

1 .48

r . 8 6

2.44

Y = 2 2

2.78

2.01

1 . . / .J

z . J >

Y = 2 1

3.94

0.53

5.004 ) \

Y = 2 7

0.85

l . + )

0.48

r .221 . 9 7

Y = 2 6

2.29

l . o J

0.56

1 . 9 7

I J

1 AI -

1 5

I O

1 , 7

AT

A 1

2.8

z . J

4A

27 9

1 0

1 l

t 2

5

r . 13 . 8

2

J

AT

A

N fertilizer = Sulphate of AmmoniaK fertilizer = Muriate of Potash*Leaching scorc and number of fertilizer applications were determined within a 12 month period commencing

7 months before the year in which yield response was recorded.

l 0

TABLE 4. SUMMARY OF SOIL SURVEY RESULTS FOR EACH TzuAL

TrialNo. Soil parent material Soil series Top-soil description Drainage

I Marine alluvium

J

i \ t , t+

5 " "

7 "

6 1

1 0

2 Riverine alluvium

6 " "

9 Organic

27 Older alluvium(granitic)

21 Granite

2 6 "

25 Rhyolite

28 Andesite

23 Shale''t A

A 1a l

8 Quartzite/shale

Dark brown, silty clay

Dark brown, clay

Dark brown, loam

Dark grey-brown, clay

Dark brown, silty clay

Dark brown, clay

Black organic. sandy clay

Dark brown, clay

Dark brown, clay

Dark brown, sandy clay

Dark brown, sandy clay

Dark brown, sandy clay

Dark yellowish brown, clay

Dark yellowish brown. ciay

Dark brown, clay

Brown, clay

Dark brown sandy clay loam/pale yellow sandy clay

Dark yellowish brown clay/strong brown clay

Dark yellowish brown clay

w.d.

m.w.d.

m.w.d.

m.w.d.

m.w.d.

m.w.d.

p. to imp. d.

m.w.d.

m.w.d.

p. to imp. d.

w.d.

w .d .

w.d.

w.d.

w.d.

m. to w.d.

w.d.

m.w.d. / imp. tom.w.d.

i inp. to m.w.d.

/m.w.d.

w .d .

Selangor

Briah

Peat

Harimau

Rengam

Kulai

Segamat

Munchong

Durian

Durian/Batu Anam

Malacca/Munchong*

Bungor

acid sulphatelateritic phase

w .d .m.w.d.lmp. to m.w.d.n f n i m n d

well drainedmoderately well drainedimperfectly to moderately well drainedpoor to imperfectly drained.

u

TABLE 5. AVERAGE O-3OCM SOIL ANALYSIS RESULTS FOR EACH TRIAL

TrialNo.

C/N%

C%

N/a

Hydrorneter Method Pioette Method

ClayVo Sand% Silt% Clay %

IaJ

/1

5

7

6 t

1 0

z

6

9

27

2 1

26

/.J

28

Z J

24

4 l

22

8

2.76

3.74

0.84

0.82

1 . 4 9

2.49

6 . 6 1

1 . 1 7

0.99

3 8 . l

0 .96

0.93

0.70

1 . 5 9

2 . r 9

1 . 6 4

0.78

U . 5 E

1 . 7 0

1 . 2 3

0 . 1 6 8

0.299

a.a760.1 06

0 . 1 1 1

0.204

0.266

0 . 1 7 0

0 . 1 7 5

1.021

0.0'/4

0.099

0.070

0 . 1 0 3

0 . 1 8 9

0 . 1 5 5

0.081

0.067

0.152

0.214

I O .+

12.5

1 1 . 1

7 .7

I J . +

12.2

24.9

6 .9

5 . 7

37.3

1 3 . 0

9 .4

1 0 . 0

15.4

l t .6

10.6

9 .6

8 .7

11.2

5 .7

17.0

11.7

24.0

21.2

22.7

21.7

rc.7I 5 . 5

1 6 . 2

t . J

1 i . 0

5 .0

/ . v

4 .3

22.5

1 0 . 5

1A.7

6.s

43.0

46.7

24.0

3 8 .8

) l . J

54.0

. / . J . /

59.5

6s .8

30.7

43.5

49.7

s6.0

73.3

40.3

40.0

34.0A a 1

44.3

a t A

2 . 1

48.0

21.3

I 3 .8

z . o

64.9

1 3 . 6

i . b

J Z . /

53.8

52.O

31.4

6.9

40.8

) 5 . b

r t .4

28.4

3t.7

27.8

31.7I+U.J

40.7

12.9

21.8

29.8

10.7

5 . U

5 . 3

14.9

I J . Z

1 1 . 1

o . /

! J . )

12.3

I O .+

42.7

59.9

22.4

48.9

48.9

52.6

I v . o

5 1 . 1

69.8

37.7

41.1A a a+ ) . 2

J Z .+

77 .7

48.1

5 1 . 8

32.6

s0.052.6

generally rather lower than the levels determined by the more accurate pipette method

(particularly in the case of trial 3 which has a high soil organic matter level). The coastal and

inland soils are most clearly distinguished by their TEC valves which reflect the different nature

of their clay minerals. Except in the case of peat, TEA was at least 80 per cent aluminium. It

should be noted that even between soils of the same series, there is a large variation in organic

matter level, texture and pH.

Soil Moisture

Measurements of AWHC for 0-30 cm and 0-90 cm soil depth are shown in Tables 6 and

7 respectively. Except for trials 4 and 5 (which have very low soil organic matter levels), the

T2

TABLE 6. AVERAGE O-3OCM SOIL ANALYSIS RESULTS FOR EACH TRIAL

TrialNo.

TEBm.e./100g

TEAm.e. /100g

TECm.e./100g

v TEBTBC

A.W.H,C.cm/30cm

pH

I

J

4

)

7

6 1

l 0

2

6

9

27

2 1

26

25

28

24

4 l

22

8

2.66.2? n

6.8

2 .5

8 . 8

1 .2

10.9

20.8

0.7

l . l

1 . 4

t . l

1 . 9

1 . 5

2 .5

2 .0

t . l

z . J

r z - 5

) . )a 4

5.6

6 . )

1 1 . 6

2 . 1

1 0 . 8

5.0

3 . 5

1 . 5

1 . 4

2.0

5 .7

2 .2

2 .5

J . J

2.6

2.0

5 .6

15.4

11.7

o . l

12.4

1 1 . 0

I ) . J

10.9

18.0

1 5 . 9

z+.J

2.5

3.4

6 .8

4 . 1

4.0

5 .8

4.6

J . l

7.9

16.9

53.0

45.3

54.7

22.7

24.5

8 1 . 0

39.9

b 6 . 5

8s.4J Z.!+

44.0

42. r

16.2

46.2

37.8

4 3 . 1

44.2

3 5 . 5

28.7

4.00

3.95

J . 6 )

1+.4 )

3.95

4.05

3.20

4.7 5

4.80

3.70

4.40

4.80

4.55

4.20

4.60

4.30

4.45

4.45

4.65

4.25

8 . 1

10.6

3 .9

6 .5

7.6

7 .9

8.0

5 . 7

4.3

1 . 8

4.0

5 .3

4 .8

4 . 5

+ . 1

z . J

TEBTEATECAWHC

Totatr extractable basesTotal extractable acidityTotal extractable cationsAvailable water holding capacity.

coastal soils all have appreciably higher available water holding capacities. Rainfall and otherestimated parameters indicating either soil moisture status or water loss from the top 90 cmsoil, averaged over a yeat and also over the 3-month periods after fertilizer application, areshown in Table 7. These results indicate that in at least 42% of months (i.e. an average of 5months per year) half of the coastal soils, in contrast to only a single inland soil (trial 4t;,have an average available water level less than 30 per cent. It is also clear that all inland soilslose considerably more water by percolation (or run-off) compared to coastal soils. A leachingscore was calculated for inland soils, based on tJre water estimated to be lost during 3 monthperiods after fertilizer application, more weight being given to water lost in months closer tothe time of fertilizer application. Water lost (in cm) beyond a 90 cm soil depth in the first,

t 3

TrialNo.

AWHCcm/90cm.

Average per year Average for 3 month periodsafter fertilizer application

Rainfall AW Dty Water Fert.cm % months loss applica-

Vo cm tions

AW Water LeachingVo loss score

cm

I

J

Ll

5

7

6 l

l 0

2

6

27

2 l

26

25

28

23

24

4 l

22

8

25.4

35.6

7 .8

8.4

25.1

29.6

20.8

22.4

18.3

10.0

4 .3

l t .2

7 .7

12.o

t . 3

r0.78.2) . J

5.4

229

190

r82

207

215

1 8 5

r99

192

205

216

248

223

246

223

243

257

196

248

214

J Z

36

39

46

59

3 l

39

42

53

48

46

) l

55

50

50

5 l

3 5

48

44

3 1

50

50

36

20

57

46

47

28

3i302 5

t 7

3 5

36

3 1

54

26

28

34

8

46

46

30

5

2 l

3 l

6 l

to7

59

83

69

90

94

50

r026 1

I

I

I

I

2

I

I

I

J

I

I

2

I

I

I

2

J I

34

l 8

29

) J

3 l

22

30

54

5 5

44

59

42

46

43

43

42

47

3 5

0.2

0.0

1 . 1

1 . 7

4.8

3 .3

1 . 6

4.4

3 .8

20.5 3.4

6 .5 3 .0

t7 .3 3 .3

1 .3 0 .8

15.7 3.2

| . 7 0 . 8

0.5 0.5

13.0 2 .8

5.4 2.0

9.7 3.0

TABLE 7. SOIL AVAILABLE WATER HOLDING CAPACITIES, RAINFALL,FREQUENCIES OF FERTILIZER APPLICATION AND PARAMETERS ESTIMATED*

FROM T}IESE PROPERTIES

AWHC = Available water holding capacilyAW = Available water in 0 - 90 cm soilDry months = Months having an average AW level less than 30 per centWater loss = Estimated percolation beyond a depth of 90 cm*Note that the water table in coastal aleas was not taken into account in the estimation of parameters.

l 4

second and third llronths after a fertilizer application was rnultiplied by 4, 2 and I respectively,and the. results added together. The surns were then converted to a score as follows: (0.3:0,

0 .3 -5 .0 :1 . 5 .1 -12 .5 :2 , 12 .6 -25 .5 :3 ,25 .6 50 .0 :4 , 50 .1 -75 .0 :5 , ) 75 .0 :6 ; and the ave rage sco re

per fertilizer application was then determined for individual years (see Table 3) and for thetotal period of investigation (see Table 7) of each trial" This scoring system ensures that if forexarriple ferti l izer is applied 4 times a yeat, the water lost after each application cannotcontribute more than one quarter of the total possible score for the year. Scores tended to behigher the greater the frequency of fertilizer applications per year because extra applicationswere made at wetter t imes of the year.

DISCUSSION

It has been shown that there is considerable variation in response to individual fertilizers,from site to site (averaged over several years) and from year to year at the same site, even

when other fertilizer rates are optimal and yield is at a fixed level. In the following sectionsthis variation in efficiency of response to fertilizer is examined in relation to the soil andclimatic factors measured. Factors which affect yield directiy are first taken into account byregressing responses on yield level. The soil and climatic factors which influence responses bytheir effect on fertilizer recovery are then identified as those factors which account for afurther appreciabie amount of response variation.

Nitrogen response

When yield responses to nitrogen fertilizer in the individual years of each trial wereexamined (after correction for yield level) in relation to soil moisture parameters, an appreciablepositive correlation was found witir soil moisture immediately after fertilizer applications incoastal trials 4. 5 and 7, whilst on the other hand a large negative correlation was found withsoil water lost irnmediately after fertilizer applications in inland trials 8, 25 and 26, and withfrequency of fertilizer applications in inland trial 21. It appears that efficiency of nitrogenfertilizer recovery is affected in quite opposite ways by soil moisture in coastal and inland

areas. This is not a consequence of the different types of fertilizer used, since in almost all the

inland trials sulphate of amrnonia was applied, which is less susceptible to leaching thanarnmonium nitrate which was applied in rnost of the coastal trials.

When annua.l nitrogen responses in coastal trials 4, 5 and 7 (shown in Table 2) wereconsidered togetl.rer, yieid level was found to account for a significant proportion of responsevariation (R' = 17.8 per cent, 28 d.f.). Soil moisture and rainfall over various periods werethen examined in relation to the nitrogen responses, and rainfall measured over a 12 monthperiod comr.nencing 7 months before yieid began to be recorded, was found to most improvethe coefficient of determination (to 32.2 per cent). Average nitrogen responses over the selectedperiod of all the trials on coastal mineral soils were very significantly correlated (R2 = 54.9 percent, 15 d.f.) with yield level and age as shown previously by Fosren (1976). The coefficientof determination was most improved (to 6Z.t per cent) by including the average level ofavailable soil water as an additional variable. Inclusion of average rainfall accounted for slightlyless variation in response (R2 = 65.0 per cent) but is much more convenient to measure andthe regression equation including this parameter is therefore presented here:

1 5

Z = dY/dN = 5.5134 - 0.2553Y - 0.0642A+ 0.0130Rwhere Z = F.F.B. yield response (in t/ha/yr) to 1 kg sulphate of ammonia applied per

palm per yearY = F.F.B. yield (in tlhalyr)A = Age in yearsR = Average rainfall (c-iyr)

Partial correlation coefficients were:

xZy.AR = -.803***, tZA.yR - -.464, rZR.Ay = .476,

and the residual error remaining after regression was 0.37. In none of the coastal trials was the

difference between predicted and observed responses more than twice this error, so none of the

trials are exceptionally anomalous. Rainfall accounts for almost as much response variation as

soil moisture probably because other factors which influence soil moisture are similar within the

coastal environment.

The regression equation predicts that at an F.F.B. yield level of 24 tlha in the 10th year

of planting on coastal soils, a response of only 1.15 t/ha can be expected if the annual rainfall

is only 185 cm/year, but if the rainfall is as high as 225 cmfyear a response of 1.67 t/ha is

predicted. This positive relationship between rainfall and efficiency of response to nitrogen

fertilizer is unexpected, particulariy since the coastal soils have a high water'table much of theyear. As discussed in the next section it is considered that it is the availability of phosphate

which is directly influenced by the rainfall, and as shown in a following paper (FosrER and

CsaNc, 1976b), phosphate increases nitrogen uptake by the oil palm.

When annual nitrogen responses in inland trials 8, 25,26 and 27 (shown in Table 3) were

considered together, yield level was found to account for a very significant proportion ofresponse variation (R' = 37 .9 per cent, 32 d.f.). kaohing score was found to be the factorwhich most improved the coefficient of determination (to 58.7 per cent) and finally inclusion

of the frequency of fertilizer applications further improved R2 to 72.3 per cent. The fitted

multiple regression equation was:

dY/dN = 5.4'771 - 0.0787 Y - 0.3205 F - 0.27s6 LF.F.B. yield response (in tlha/yr) to 1 kg sulphate of ammonia applied perpalm per year,

Y = F.F.B. yield (in tlhalyr),F - No. of ferti l izer applications made per year, andL = kachins score.

Partial correlation coefficients were:

rzypL = -0.514' r ' * , rZF.yL = -0.500** and r71.yp = -0.456** ,

and the residual error remaining after'regression was 0.68. The four iniand trials from whichthis relationship was derived were those which gave the largest responses to nitrogen fertilizer.Correlations were much poorer with leaching scores derived from water lost in periods longerthan three months. When results from inland tials 22, 23 and 28, which gave only moderatgnitrogen responses, were included, the correlation with yield level was maintained, but thecorrelation with leaching score and frequency of fertilizer application disappeared. When resultsfrom inland trials 21 , 24 and 41, which gave negative responses to nitrogen fertilizer wereincluded, even the yield level correlation with nitrogen response disappeared. It is concluded

Z =where Z =

t 6

that other factors are probably l imiting nitrogen response in these latter trials (probably the1evel of other ferti i izers in most cases, since ferti l izer rates were low in most of these trials) withthe result that nitrogen response is either negative or only moderate and cannot be directlyrelated to leaching intensity. The fitted regression equation indicates that at an F.F.B. yieldievel of 24 tlhalyr, a response of 3.3 tlhalyr to 1 kg sulphate of ammonia per palrn can beexpected if the leaching score is zero and ferti l izer is applied only once a year. Thiscorresponds to a ferti l izer recovery of 88 per cent, if we use tl 're nutrient requirernent data ofNc er al., (1968) quoted in the previous paper in this series (FoStER. 1976). If leaching scoreis instead -, 6, then the regression equation predicts a much lower ferti l izer recovery of 40 percent. and if the ferti l izer is spiit and applied four times a year. expected recovery is then aslow as 16 per cent (equivalent to a response of 0.65 tlhalyr). These results, admittedly fromonly a few triais, suggest that nitrogen ferti l izer should be applied only once a year at a tirnewhen litt le rain is expected. The negative correlation of response with frequency of applicationsis contrary to expectation. The simplest explanation is that additional ferti l izer applications tendto be rnade at wetter t imes of the year, and the leaching score alone is too crude to fullyaccount for the greater loss by leaching and run-off which thus occurs. An alternativeexplanation is that the ground cover immobilises more ferti l izer when it is applied morefrequently (ferti l izer was broadcasted in trials 26 and 27). Further investigations are necessary toclarify the effects of t ime and frequency of nitrogen ferti l izer applications on the efficiency ofnitrogen recovery by oi1 palms in different environments in Malaysia.

Phosphate Response

As shown previously (FosTER, 1976), palm age accounts for 44.1 per cent of thevariation in average phosphate response recorded in trials on coastal soils. Of the various soiland climatic factors measured, annual rainfall accounted for most additional variation, increasingR2 to 58.2 per cent. Inclusion of yield level as a third independent variable did not have mucheffect, but replacement of palm age by yield level gave a similar R2 (60.1 per cent) and theregression equation including this variable rather than age is presented:

whered Y / d P = 1 . 1 4 3 _ ' 0 . 1 9 7 Y + 0 . 0 2 3 RF.F.B. yield response (in t/haiyr) to 1 kg Christmas Island rock phosphateapplied per palm per yearF.F.B. yield (in t/ha/yr)average rainfall (cmiyr).

Partial correlation coefficients were:

r zy .R - - ' . 703* *an , l R = ZR .y

= . 701* * ,

and the residual error remaining after regression was 0.36. None of the residuals exceeded more

than twice this error.

The regression equation predicts that at an F.F.B. yield level of 24 tlha. a response of

only 0.67 tfha can be expected if the annual rainfall is only 185 cm/yr, but if the rainfall is as

lrigh as 225 cmlyear a response of 1.59 tiha is expected. It appears that recovery of P fertilizcr

applied to coastal soils is often limited by inadequate soil moisture. despite the presence of a

high water table much of the year. This phenomenon is confirmed by a significant positivc

correlation found between leaf P levels and soil moisture, immediately prior to sampling on

coastal soils (FosrER and CneNc, 1976a'). The solubil ity of phosphate in soil solutions is

7 -L

7 -

l -

R =

1 1

Z =where Z =

low, which has two important consequences affecting crop recovery. Firstly any phosphate

applied as fertilizer will not penetrate to any depth in the soil' Thus the water table in coastal

soils witi not generally have any effect on P availability, and P uptake will be restricted as soon

as oiily the topsoil dries out. Secondly because P can maintain only a low concentration in the

soil solution, movement to plant roots is almost entirely by diffusion, a process strongly

influenced by moisture stress. Coastal topsoils generally have a higher water holding capacity

compared with inland topsoils (see Tabte 6). so that they require more water to achieve a

simiLr percentage level of available water. In consequence the water potential in coastal topsoils

is on average lower than that in inland topsoils and it is therefore not surprising that efficiency

of p fertilizer recovery in coastal soils is dependent on adequate rainfall. Fertilizer N is readily

leached down to iower soil depths where moisture is generally adequate in coastal soils' and

nitrogen movement to plant roots is largely by rnass flow, so that the uptake of this nutrient is

rnu.h 1.r, likely to Ue timitea by available water. As suggested earlier, the correlation of N

response with annual rainfall in coastal areas is therefore probably due to the fluctuating

influence of phosphate on N uptake. No other factors were found to significantly increase the

amount of P response variation already accounted for. Inclusion of soil TEB had the most

effect, increasing R2 to 6l .1 per cent.

In a preceding paper (Fosrun, 19'76). it was shown that 36.3 per cent of phosphate

variation in trials on inland soils could be accounted for by yield level and planting density

(when anomalous data from trial 24 was omitted). Of the various soil and climatic factors

measured, soil pH was found to account for the most amount of additional variation (increasing

R2 to 51.9 per cent, 14 d.f.) the regression equation being:

dY/dP = -21.40 .0942Y + .0689D + 3.535H

F.F.B. yield response (in t/halyr) to 1 kg christmas Island rock phosphate

appiied per Palm Per YearY = F.F.B. yield (in rfhalyr)

D = Planting density in palms per hectare,

H = Mean soil pH in 0 30 cm dePth'

Partiai correlation coefficients were:

rZy.DH = - .295, rZD.yH - .660** and r2g.yp = '496*.

and the residual error remaining after regrcssion was 1.04. For trial 8, the difference between

predicted and actual P response (at a yield level of 31 t/ha) was just over twice this error but

tmission of data from this trial did not improve the regression. The prediction equatton

indicates that at a yield level of 24 tlha and a planting density of 136 palms per hectare,

responses of 0.73 t/ha and 2.50 t/ha are expected at soil pH values af 4.25 and 4.15

respectively. Tliis apparent influence of soil pH on P response indicates that arnendments which

affect pH (such as sulphate of amrnonia or bunch ash) ma;' appreciably affect P response.

Since the partial correlation of P response with soil pH is positive, it is evident that.

within the very acid range of soil pH values encountered in this study, the negative effect of

soil pH on the rate of solubilization of rock phosphate is ntuch less important than other

positive effects of soil pH whicir influence phosphate availabil ity. HINGSToN et al., (1967)

have described how the absorption of phosphate by soil rninerals is inversely related to soil qH,

a phenomenurn which explains why efficiency of P response increases with pH. P sorption also

depends on the level of active soil iron and aluminium which is often related to the clay

content. Thus OweN (1941) found that for inland Malaysian soils, phosphate retention was

1 8

closely related to clay content, but in this study P response was not found to be significantly

related to clay content. It is suggested that a direct measurelnent of P sorption or active iron

and aluminium might have accounted for a significant additional amount of P response

variation.

Potassium response

Yield level was found to account for 32.1 per cent of the variation in K response on

coastal soils (FosrnR, 1976). As witi i phosphate, the movement of potassium to plant roots is

rnainly be diffusion. which is sensitive to changes in soil moisture. Thus it has been shown(FosrER and CneNc, 1976a) that palm leaf K levels fluctuate with changes in the availablewater level of coastal soils. However K responses in the individual years of each coastal trial.

and averaged over all years of each coastal trial, were not found to be significantly related toany rainfall or soil moisture data. It appears that soil moisture does not have a major effect onK response, perhaps because potassium is more rnobile than phosphate and can move down tothe subsoil which dries out less rapidly than the topsoil. No soil properties were found to besignificantly correlated with K response on coastal soils either.

When annual potash responses in .inland trials 8, 25, 26 and 27 (shown in Table 3) wereconsidered together, yield level was found to account for 17.7 per cent of variation. Inclusionof leaching score and frequency of fertilizer application very significantly improved thecoefficient of determination to 49.0 per cent (13 d.f.). The fitted regression equation was:

Zwhere Z

YF

and L

dY/dK = 5 .6113 0 .0783Y -

F.F.B. yield response (in t/ha/yr)palm per year,F.F.B. y ie ld in t lha lyr ,No. of fertilizer application madelraching score

0 .3315F 0 .2724Lto I kg muriate of potash applied per

per year,

Partial correlation coefficients were:

rzy.Ft = 0.291, rzp.yf = - -0.350 and r7y.yp = 0.304,

and the residual error after regression was 1.07. Thus in individual years the same factors,leaching intensity immediately after fertilizer applications and frequency of fertilizerapplications, ir.rfluence N and K responses on inland soils, but the partiai correlation coefficientsindicate that their effect on K response is not so great.

When results were averaged over the selected period of each of the l0 trials on inland

soils, yield level was found to account for 29.3 per cent of K response variation (FOSTER'

1976). Of the various soil properties measured, per cent clay accounted for the most amount of

additional response variation and pH further appreciably improved the coefficient of

determination to 53.6 per cent (16 d.f.). The amount of K response variation accounted for

was exactly the same whether the clay results were determined by the pipette or the

hydrometer method, and the regression equation presented includes clay determined by the

simoler hvdrometer method:

1 9

wheredY/dK = -2.7525 - 0.0708Y - 0.0255C + l.624OH

F.F.B. yield response (in t/ha/yr) to I kg muriate of potash applied pet

palm per year,F.F.B. yield ievel in tlhafyr,Soil per cent 91ay (determined by trydrometer method),Soil pH.

Partial correlation coefficients were:

rZy.CH = .408, rZC.yH = -.450 and r2g.yg = .418

and the residual error after regression was 0.65. None of the trials had residuals which exceededtwice this error. The regression equation predicts that at a yield level of 24 tlha, a soil claycontent of 35 per cent and a pH of 4.75, a K response of 2.37 t/ha can be expected on inlandsoils. If the soil clay content is instead 70 per cent, then a reduced response of 1.48 t/ha ispredicted, and if also the pH is as low as 4.25, a response of only 0.6'1 tlha is predicted. Thelatter is almost exactly the same as the average response of 0.68 tiha which is predicted at ayield level of 24 tlha by the regression equation for coastal soils.

The magnitude of crop K response at a fixed yield level is dependent on the amount ofpotash required to maintain soil K intensity against losses due to crop removal, leaching andfixation. It has been shown above that at individual sites on inland soils, K response variesfrom year to year according to intensity of leaching. However when cornparing responses atdifferent sites on inland soils averaged over several years, it is soil properties which are foundto account for most variation. The main cause of variation in K response between inland sitestherefore appears to be due to dtfferences in soii K buffer capacity, w.hich determines theamount of K required to counteract any drop in soil K intensity. A direct measure of thisproperty would probably have been better related to K response, ratJrer than clay content andpH which are only two of the major factors which determine K buffer capacity.

The nature of the soil clay is another important factor determining buffer capacity, and itis probably the presence of i l l i te which resuits in the much higher buffer capacity (SINGH,

1970) and hence lower K response found in coastal soils. I l l i te causes "tlxation" of added K, aphenomenon which l. lc. (1965) has shown to be appreciable in coastal but not inland soils inWest Malay,sia However K buffer capacity or "fixation" measured in a laboratory do not takeinto account variation in weather conditions wirich influence these properties in the field. ThusK "fixation" depends on the aurount of wetting and drying undergone by a soil. and becausethis was not taken into account, may be the reason rvhy no factor (other than yield level) wasfound to be significantly related to variation in K response on coastal soils.

CONCLUSION

There is considerable variation in oil palm F.F.B. yield response to individual fertilizers,

even when all other fertilizers are at optimal levels, yield (and therefore fertility level) is at a

fixed level and palm factors are similar. This variation in efficiency of response to fertilizers'is

largely due to differences in soil and climate.

In the trials selected for the present study. response to N and P f'ertilizers on coastal soils

was found to vary with annual rainfall. It appears that inadeqtrate soil moisture in the surface

zZ

YcH

20

layer of coastal soils limits crop uptake of P, which in turn influences crop N recovery.Response to K fertilizer on coastal soils was not found to be significantly related to any soil orclimatic factors, but was generally much lower than K response on inland soils. probablybecause coastai soils have a high K buffer capacity due to tire presence of iilite in their clayfraction.

Response to both N and K fertilizers in individual years of trials on inland soiis wasnegatively related to both intensity of leaching afler fertilizer appllcatiorrs and frequency offertilizer applications. On the crther hand K response on inland soils, when averagecl over severalyears, was found to be positively related to soil pH and negatively related to soil cla1r, factorswhich contribute to soil K buffer capacity. Response to P fertilizers on inland soils waspositively related to soil pH, probably because this soil property is related to P sorption.

ACKNOWLEDGEMENTS

The oil palm fertilizer trlals were carried out by Chernara Research Station. Harrisons anclCrosfield Oil Palm Research Station, Dunlop Research Centre and United Plantations ResearchDepartment. Thanks are extended to Duniop Estates Bhd., Harrisons and Crosfield (Malaysia)Sdn. Bhd., Kuntpulan Guthrie Sdn. Bhd., Unipamol Malaysia Sdn. Berhad and UnitedPlantations Berhad for permission to use data from these trials.

We thank the Head anci Staff of the Soil Science Branch, MARDI, for assistance in thesurvey of trial sites, and the Head and Staff of the Soils and Crop Management Dinsion,RzuM, for co-operation in the analysis of soil samples.

We are gratefui for the advice and assistance received from the Head anci Staff of theMARDI. Statistics Branch, and acknowledge the conscientious work of assistant members of theMARDI Oil Palm Nutrition Team who collected and anaivsed soil sarlples and assisted in theprocessing of the data.

SUMMARY

In a selection of oil palm fertiiizer trials carried out in West Malaysia, iresh fruit b'.rnch yieldresponses to n-, P and K fertilizers, at optimal levels of other fertillzers and after atijustment foryield level and palm factors, have been examined in relation to soil and cliinatic factors. In thetrials on coastal soils, average N and P responses were positively related tc annual rainfall. In thetrials on inland soiis, N and K responses in inc'rvidual -vears rvere negatively related to both intensityof leaching after fertilizer applications and frequency' ol terrilizer applicalions, whilst K responsesaveraged over several years were positively reiated to soil pH and neeativeil related to soil claycontent. on inland soiis, average P responses were also positively related to soil pH.

REFERENCES

FoSTER, H.L. (1976). Yield response of oilresponse functions, MARDI Res. Bull. Vol.

to fertilizers in West Malavsia L Yieldt. 41 - 63.

paim4 No.

Fosrpn, H.L. and CHnNc, K.C. (1976a). The diagnosis of the nutrienr status of oil palms inWest Malaysia. Proc. Int. Agric. Oil Palm Conf. 1976, Kuala Lumpur.

21

Fostr,R, H.L. and CuaNc, K.C. (1976b). Yield response of oil palm to ferti l izers in West

Malaysia III. lraf nutrient levels. MARDI Res. Bull. VoL 5 No. 1.

HTNGSToN, F.J. , ArKINsoN, R.J. , PosNER, A.M. and 'Qutnr , J .P. (1967). Speci f icabsorption of anions. Natirre, 215, 1459 - 61.

Nc, S.K., (1965). The potassium status of some Malayan soils. Malay. Agric. J. 45, 143 -

1 6 1 .

Nc, S.K., Tsllttoo, S. and DE SouzA, P. (1968). Nutrient content of oil palms in Malaya.II. Nutrients in vegetative tissues. Malay. Agric. J., 46, 332 - 391.

Owpu, G. (1941). Retention of phosphates by Malayan soils. I. The nature of phosphateretention in different soil types. J. Rubb. Res. Inst. Malaya. 12, | - 29"

SINcg, M.M. (1970). Exchange reactions of potassium, magnesium and aluminium on someMalayan soils. Ph.D. Thesis, University of Maiaya.

22