Coconut Research Institute Repository

Wijebandara, D.M.D.I.

COCOS (2004), 16, 65 - 73 
Printed in Sri Lanka 
SOIL PHOSPHORUS TEST METHODS CALIBRATION BY FIELD 
EXPERIMENTAL DATA FOR THE SOILS OF LOW COUNTRY 
INTERMEDIATE ZONE OF SRI LANKA 
D M D I Wijebandara 
Coconut Research Institute, Lunuwila, Sri Lanka 
ABSTRACT 
Green house studies showed that the 2.5 % Acetic acid (HAc), Olsen's 
bicarbonate (0.5 M NaHC0 3 ) , Anion Exchange Resin (AER) and Anion 
Exchange Resin + Cation Exchange Resin (AER + CER) methods were 
satisfactory for the estimation of plant available phosphorus (P) of soils of 
the Low Country Intermediate Zone of Sri Lanka. The objective of this 
study was to calibrate the four extraction methods by field experiments. 
Relative yield of Pueraria phaseoloides grown in field on five soil series 
treated with and without P fertilizer, but with basal treatment of nitrogen, 
potassium and magnesium fertilizer were employed as the plant index for 
soil P status. Soil P status of each soil prior to treatment was determined 
by the four extraction methods. 
The 2.5 % HAc - P values showed the best correlation with relative dry 
matter yield of Pueraria by fitting significantly to the Cate and Nelson model 
with R 2 of 0.628 (P<0.01). Both AER - P and AER + CER- P values 
showed the poor correlation with R 2 of 0.460 (P<0.05) compared to HAc -
P. NaHC0 3 -P showed poorest correlation with R 2 of 0.449 (P<0.05). The 
2.5 % HAc - P was found to be superior to others as it accounted for 62.8 
% of the variation of relative yield against 45 - 46 % by the other 
extractants. Threshold P levels as determined by the correlation data were 
7.8, 3.84, 5.34 and 8.47 mg/kg for 2.5 % HAc - P, AER - P, (AER + CER) -
P and NaHC0 3 - P respectively. The 2.5 % HAc method was found to be 
the most suitable P extraction method for Low Country Intermediate Zone 
of Sri Lanka. 
INTRODUCTION 
Soil phosphorus (P) estimation by laboratory methods is of major 
importance in an effective phosphate fertilizer recommendation 
programme. A large number of soil P tests for plant available soil P 
estimation are found in literature. But none of the methods can be 
recommended for any soil, unless such methods are evaluated and 
properly calibrated with respect to a particular soil - plant combinations. 
65 
Evaluation of methods for the determination of available P of some coconut 
growing soils in Low Country Intermediate Zone of Sri Lanka by green 
house pot experiments revealed that 2.5 % Acetic acid (HAc) (Anon, 1985), 
Olsen's Bicarbonate (0.5 M NaHC0 3)(Olsen era/., 1954), Anion Exchange 
Resin (AER) and Anion Exchange Resin + Cation Exchange Resin (AER + 
CER) (Somasiri and Edwards, 1992) extraction were suitable (Wijebandara 
and Somasiri, 1994). But the P values by the above methods cannot be 
interpreted meaningfully unless each of them are calibrated by field 
experiment. The objective of the present study was to calibrate the 2.5 % 
HAc method, 0.5 M NaHC0 3 method, AER method and AER + CER 
methods by field experiments with respect to Pueraria phaseoloides which 
is an important cover crop grown under coconut. 
MATERIALS AND METHODS 
A field experiment was design to study the plant response to the applied P 
in ten coconut growing soils. Field experiment was conducted in top (A 
horizon) and sub (B horizon) soils of five different soil series located in 
Bandirippuwa estate of the Coconut Research Institute, Lunuwila 
(Intermediate Zone, Low country). The soils were Boralu series, Pallama 
series, Madampe series, Sudu series and Lunuwila series. The brief 
description of soil series, chemical and the physical characteristics of each 
soil is given in Table 1. 
66 
Table 1: Description of each soil series, Chemical and physical characteristics of soils used for the field experiment 
ON 
Great soil group Soil series Description pH 1:5 EC Sand Silt Clay Total N Organic 
soil: H 2 0 //mho/cm % % % Matter 
% 
Red Yellow Podzolic (RYP) Boralu (BOR) Top soil (A) 4.86 41.68 77.87 17.05 3.45 890 1.76 
Red Yellow Podzolic (RYP) Boralu (BOR) Sub soil (B) 4.54 25.07 78.20 10.98 4.58 525 1.12 
Red Yellow Podzolic (RYP) Pallama (PAL) Top soil (A) 5.19 37.15 85.54 7.08 3.40 470 0.97 
Red Yellow Podzolic (RYP) Pallama (PAL) Sub soil (B) 4.83 34.13 87.14 8.50 3.28 336 0.63 
Latosols and regosols on old red and yellow sands Madampe(MDP) Top soil (A) 5.32 32.62 94.51 2.78 3.10 265 0.47 
Latosols and regosols on old red and yellow sands Madampe(MDP) Sub soil (B) 5.23 25.07 88.42 3.30 3.90 220 0.33 
Latosols and regosols on old red and yellow sands Sudu (SUD) Top soil (A) 5.09 28.09 97.73 1.58 3.45 377 0.90 
Latosols and regosols on old red and yellow sands Sudu (SUD) Sub soil (B) 5.01 26.58 93.57 2.53 3.03 345 0.68 
Alluvial soils Lunuwila (LUN) Top soil (A) 5.32 29.60 94.62 0.90 2.68 291 0.53 
Alluvial soils Lunuwila (LUN) Sub soil (B) 5.27 22.05 97.60 1.55 2.80 235 0.36 
A-A horizon (Top soil), B - B horizon (Sub soil) 
The beds of dimensions 1.5 m x 1.5 m were prepared in Boralu series, 
Pallama series, Madampe series, Sudu series and Lunuwila series soils. In 
each soil, beds were prepared including two depths; viz., the top soil 
ranging from 0-20 cm from the surface (A horizon) and the sub soil 
obtained after completely removing the top soil. The surface gap occurred 
due to removal of top soils were filled with the sub soil taken from the 
surrounding areas. The beds were arranged in the randomized block 
design with three replicates in each of which there were two treatment 
plots, +P and - P . For each depth, beds were prepared separately. 
Two phosphorus treatments were applied viz., no P application (-P), P 
application (+P) at the rate of 595.24 kg of Ca(H 2 P0 4 ) 2 (TSP) per ha. Basal 
dose was applied at the rate of 95.24 kg of (NH 4 ) 2 S0 4 per ha. as N, 119.05 
kg of KCI per ha. as K and 59.52 kg of MgS0 4 .7H 2 0 per ha. as Mg. 
Pre-germinated Pueraria phaseoloides seedlings were planted at distances 
of 30 cm between rows and 15 cm between plants in each bed. Three 
months after planting, vegetative part of Pueraria were harvested within an 
area of 0.5 m 2 and fresh and dry weights of harvested materials were 
recorded. Percent Relative yield (RY%) of the crop in each soil was 
calculated as, 
RY % = Yield at - P treatment x (100) 
Yield at + P treatment 
The dry weight of vegetative parts was taken as the yield of the Pueraria. 
Total Phosphorus content of vegetative parts of Pueraria was estimated by 
wet digestion with H N 0 3 : HCI0 4 mixed at 1 : 4 ratio (Manual of analytical 
methods, 2000) 
Soils were sampled prior to treatment application up to a depth of 30 cm 
from each replicate and bulked. Air dried 2 mm sieved soils were analyzed 
for available P by 2.5 % HAc method, 0.5 M NaHC0 3 , AER method and 
AEP + CER method. Phosphorus in solution resulting in each extraction 
was estimated by the molybdenum- blue method (Murphy and Riley, 1962). 
2.5% Acetic acid extraction: (Anon, 1985) 
A sample of 2.5 g soil was shaken with 100 ml of 2.5 % (v/v) acetic acid 
solution for 2h. The mixture was filtered through Whatman no 42 filter 
paper and the filtrate was analyzed for P. 
1 
68 
Olsen's Bicarbonate extraction: (Olsen et. al., 1954) 
Five grams of soil was shaken with 100 ml of 0.5 m sodium bicarbonate 
solution (pH 8.5) (with 5 ml of 0.5 % polyacrylamide in one liter of NaHC0 3 ) 
for 30 minutes. The mixture was filtered through Whatman 42 filter paper 
and the pH of the filtrate was adjusted to 5 using paranitrophenol indicator, 
and the filtrate was analyzed for P. 
Anion Exchange Resin extraction: (Sibbesen, 1977 and 1978) 
Five grams of soil was weighed into a 250 ml polypropylene bottle, and 100 
ml distilled water and 4 ml of anion exchange resin (IRA 400 CI") in a mesh 
bag was added to each bottle. The contents were shaken in an end-over-
end shaker for 4 h. The resin bags were recovered, washed with distilled 
water to make them free of soil residues and absorbed phosphate onto 
resin was eluted by shaking each resin bag in 50 ml of 1M NH 4CI solution 
for 30 minutes, The elute was analyzed for P. 
Anion Exchange Resin + Caion Exchange Resin (AER + CER) 
extraction: (Somasiri and Edwards, 1992) 
Five grams of soil was weighed into a 250 ml polypropylene bottle, and 100 
ml distilled water, 3 ml of cation exchange resin (Duolite 255, NH4 +) and 4 
ml of. anion Exchange resin (IRA 400, CI") filled into separate mesh bags 
were added to each bottle. The contents were shaken in an end -over-end 
shaker for 4 h. The resin bags were recovered and washed with distilled 
water to make them free of soil residues. Phosphate sorbed onto resins 
were eluted by shaking each pair of resin bags in 50 ml 1 M NH4CI solution 
for 30 minutes, and the elute was analyzed for P. 
Analytical data were analyzed according to Cate and Nelson statistical 
procedure (Cate and Nelson, 1971) and threshold levels for soil P were 
determined. 
RESULTS AND DISCUSSION 
According to pH measurement in 1:5 soil- water suspension (Table 1) 
seven soils (including A and B horizon) prior to P treatment showed 
strongly acidic reaction (pH 5.0 - 5.5) and three soils showed very strongly 
acidic reaction (pH 4.5 - 5.0) (Troug, 1948). Laboratory estimates of P in 
different soils obtained by individual methods were quite variable (Table 2). 
69 
Table 2 : Extractable phosphorus content of soils used for the field 
experiment as estimated by different methods 
Soil series Soil P test method 
2.5% HAc 
mg/kg 
Olsen's AER - 4h 
mg/kg mg/kg 
AER + CER -
4h 
mg/kg 
BOR-A 
BOR-B 
PAL-A 
PAL-B 
MDP-A 
MDP-B 
SUD-A 
SUD-B 
LUN-A 
LUN-B 
101.05 
5.75 
82.41 
13.25 
7.82 
3.80 
6.94 
5.12 
7.42 
8.10 
22.45 
8.23 
4.19 
9.76 
7.47 
4.53 
6.81 
8.47 
13.27 
14.73 
7.00 
3.39 
5.43 
3.84 
2.86 
2.37 
3.84 
3.21 
3.58 
3.30 
21.31 
5.34 
17.08 
4.73 
4.53 
3.54 
4.87 
4.04 
4.43 
4.40 
A - A horizon (Top soil) B - B horizon (Sub soil) 
Also the different methods gave different estimates for the P status of the 
same soil. Extractable P of the ten soils by 2.5 % HAc (HAc - P) varied in 
a wide range (3.80 - 101.05 mg/kg). But the ranges of extractable P by 0.5 
M NaHC0 3 ( N a H C 0 3 - P), AER (AER-P) and AER + CER (AER + CER-P) 
were quite narrow compared to HAc-P (4.19 - 22.45 mg/kg, 2.37 - 7.00 
mg/kg and 3.54 - 21.31 mg/kg respectively). Although anion exchange 
resin shows a neutral reaction in the soil / solution / resin system, anion 
exchange resin in the presence of cation exchange resin extracted a 
greater quantity of soil P than anion exchange resin alone. This tendency 
is very similar to previous observations by Vaidyanathan and Talibudeen 
(1970). The Anion exchange resin extractable P values in soils of the field 
experiment obtained by employing 4h shaking time were much lower than 
that of other extractants (2.5 % HAc, 0.5 M NaHC0 3 and AER + CER - 4h) 
ranging from 2.37 mg/kg to 7.00 mg/kg. But the values by all four methods 
showed highly significant linear correlations between each other (P < 
0.001) with correlation coefficients falling in the range of 0.806 < r < 0.999. 
The highest correlation was obtained between HAc-P and AER + CER-P (r 
= 0.999) and the lowest was between HAc-P and NaHC0 3 - P (r = 0.806). 
The goodness of fit of soil test data and corresponding plant indices to Cate 
and Nelson statistical model can be used to evaluate the suitability of soil P 
testing methods. Such a soil test can also be calibrated to get the critical 
soil P levels. Cate and Nelson statistical model (Cate and Nelson, 1971) 
provides a method for determining the dividing line, or the critical level 
between two categories of soils; viz., high probability of response (low soil 
P status) and low probability of response (high soil P status) to applied P. 
Each soil P data set (Table 2) was arranged in the ascending order with 
70 
corresponding RY% values for Pueraria (Table 3), and by a simple iterative 
process a series of R 2 values were obtained for arbitrary divisions made 
into high and low P status made at various levels of soil P. 
Table 3: RY% of Pueraria phaseoloides in each soil series 
Soil series RY% 
Based on dry weight 
B O R - A 109.01 
B O R - B 67.81 
PAL - A 95.43 
PAL - B 94.15 
M D P - A 62.82 
M D P - B 74.47 
S U D - A 59.45 
S U D - B 46.49 
L U N - A 84.66 
L U N - B 82.24 
A - A horizon, B - B horizon 
The R 2 was calculated for each arbitrary division and the division at which 
R 2 becomes maximum is taken as the critical level of soil P for the 
particular soil-plant combination, with respect to the method tested. The 
value of R 2 is also an indication of the degree of fitness of the data set to 
the model. The calculated R 2 values, and the critical level for each soil P 
test are given in Table 4. 
Table 4 : Highest R 2 values and the soil critical levels obtained by Cate 
and Nelson statistical procedure 
Soil P test method R 7 
Dry weight basis Critical level mg/kg 
2.5 % Acetic acid 0.628** 7.80 
Olsen bicarbonate 0.449* 8.47 
AER - 4h 0.460* 3.84 
AER + CER - 4h 0.460* 5.34 
P < 0 . 0 0 1 , * * P < 0 . 0 1 , * P < 0 . 0 5 
Among the different P test methods used in the field experiment. 2.5 % HAc 
- P values showed the highest correlation with relative yields of Pueraria 
fitting significantly to the Cate and Nelson model with R 2 of 0.628 (P < 0.01) 
for dry weight of vegetative parts. Thus the 2.5 % HAc-P values could 
71 
account for the variation of 63 % of the production of vegetative parts of 
Pueraria in different soil condition in the field. The correlation coefficients 
R 2 between AER - P at 4h extraction and relative yields of dry weight of 
Pueraria was 0.460 (P<0.05) which explained only 46 % of the variation in 
the production of dry weight of Pueraria. The situation was much the same 
with (AER +, CER) - P also. Both AER - P and (AER + CER) - P showed 
poor correlations with relative yields of Pueraria compared to 2.5 % HAc-P. 
0.5 M NaHC0 3 - P showed a poorest correlation (R 2 = 0.449, P<0.05) with 
dry weight of the vegetative parts of Pueraria explaining only 45 % of 
variation in dry matter production (Table 4). There was no clear 
geometrical relationship between soil P values by different extraction 
methods and leaf P concentration and P uptake of Pueraria. 
The results of the field experiment showed that, out of the soil P test 
methods examined, 2.5 % HAc - P gave the best correlation with plant yield 
under different soil conditions. The correlation was poorest with 0.5 M 
NaHC0 3 - P values. Threshold P levels as determined by the correlation 
data were 7.8, 3.84, 5.34 and 8.47 mg/kg for HAc - P, AER - P, (AER + 
CER) - P and NaHC0 3 - P respectively. The 2.5 % HAc method is simple 
and much economical for soil phosphorus estimation compared to other 
three methods. The 2.5 % HAc can also be used as a multi - element 
extractant for the estimation of soil potassium and magnesium 
(Anonymous, 1985). Therefore, it is very attractive as a routine soil testing 
method, compared to single element estimation methods. 
CONCLUSION 
Results showed that 2.5 % HAc-P accounted for 63 % of the variation in 
relative dry matter weight and therefore considered the best extractant for 
the determination of available P of soil. As other methods also accounted 
for only 45 - 46 % of the variation of relative dry matter weight, they are 
inferior to HAc method. The threshold level for 2.5 % HAc - P was found 
to be 7.8 mg/kg serves as an index for separating soils on the basis of P 
fertility in respect of leguminous creeping cover crops. As 2.5 % HAc 
method is a multi-element, rapid and economical extraction method, it is 
more attractive than other methods for routine work in soils of Low Country 
Intermediate Zone of Sri Lanka. 
72 
REFERENCES 
Anon, (1985). Advisory soil analysis and interpretations, Bulletine of 
Macauley Institute for Soil Research and Scottish Agricultural 
Colleges, Liason Group p. 4. 
Cate, R.S. Jr. and Nelson, L.A. (1971). A simple statistical procedure for 
partitioning soil test correlation data into two classes. Soil Science 
Society of American Proceedings 35,658 - 660. 
Manual of analytical methods of soils and plant Analysis. (2000). Soils and 
Plant Nutrition Division, Coconut Research Institute, Lunuwila, Sri 
Lanka. 
Murphy, J. and Riley, J.P. (1962). A Modified single solution method for the 
determination of phosphate in natural waters. Anal. Chim. Acta. 27, 
31-36. 
Olsen, S.R. Cole, C V . Watanabe, F.S. and Dean, L.A. (1954). Estimation 
of available phosphorus in soils by extraction with sodium 
bicarbonate. U. S. D. A., Washington, D. C. Circ. No. 939, p. 1-19. 
Sibbesen, E. (1977). A simple ion-exchange resin procedure for extracting 
plant-available elements from soil. Plant and Soil, 46, 665-669. 
Sibbesen, E. (1978). An investigation of the anion exchange resin method 
for soils phosphate extraction. Plant and Soil 50, 305-321. 
Somasiri, L.L.W and Edwards, A.C. (1992). An ion exchange resin method 
for nutrient extraction of Agricultural Advisory soil samples. 
Communication in Soil Science and Plant Analasis 23 (7 & 8), 645 -
657. 
Vaidyanathan, L.V. and Talibudeen, O. (1970). Rate processes in the 
desorption of phosphorus from soils by ion-exchange resins. 
Journal of Soil Science 21,173-183. 
Wijebandara, D.M.D.I. and Somasiri, L.L.W. (1994). Comparison of routine 
laboratory methods for the estimation of plant available phosphorus 
in soils of the Low Country Intermediate Zone of Sri Lanka. 
Tropical Agricultural Research 6, 211 -222. 
73 


Soil phosphorus test methods calibration by field experimental data for the soils of low country intermediate zone of Sri Lanka

Samarajeewa, A.D.

Senaratna, R.P.B.S.H.S.

Perera, K.C.P.

COCOS (2004), 16, 37 - 42 
Printed in Sri Lanka 
EFFECT OF DIFFERENT CONTROL METHODS OF IMPER ATA 
CYLINDRICA ON COCONUT (COCOS NUCIFERA) YIELD IN LOW 
COUNTRY DRY ZONE OF SRI LANKA 
A D Samarajeewa, R P B S H S Senaratna and K C P Perera 
Coconut Research Institute, Lunuwila, Sri Lanka 
ABSTRACT 
Five methods of control of Imperata cylindrica (L.) Beauv namely a) 
harrowing with disc harrow, b) Glyphosate (N- Phosphonomethyl Glycine) 
2.88 kg a.i / ha, c) Glyphosate 1.44 kg a.i/ha, d) circle weeding with 
Glyphosate (1.44 kg a.i/ha) along with mechanical slashing rest of the area, 
and e) mechanical slashing were evaluated to determine the cost effective 
method of control of Imperata cylindhca, and to ascertain the effect of 
coconut -Imperata competition on yield of coconut in Low Country Dry zone 
in Sri Lanka. An unweeded plot was used as the control. Experiment was 
arranged in a Randomized Complete Block design with three replicates. 
Treatments were applied twice a year in six months interval. Glyphosate at 
the rate of 2.88 and Glyphosate 1.44 kg a.i/ha gave a significant reduction 
(P<0.05) of weed biomass when compared to other treatments. A significant 
increase (P< 0.05) of coconut yield was observed due to control of Imperata 
in plots with these treatments at two years after imposition of treatments 
.When cumulative average yield of coconut was considered for three 
consecutive years, control of Imperata with Glyphosate gave a 54% 
increase (P<0.01) of nut yield when compared to the unweeded control. 
Cost - benefit analysis of different control methods revealed that the 
application of Glyphosate at the rate of 1.44 kg a.i/ha was the most cost 
effective (undiscounted B/C ratio: 5.9) method of control of Imperata in 
sandy soils in the Low Country Dry Zone of the Coconut Triangle. 
INTRODUCTION 
Coconut is by far the most extensively cultivated plantation crop in Sri 
Lanka. The growth habit of the palm and its' canopy structure requires a 
wide spacing, which permits abundant sunlight available to the understory. 
As a result the unutilized space under coconut could get invaded with 
weeds, which compete for soil moisture and nutrients reducing the growth 
and yield of coconut palm and obstruct routine agronomic practices 
(Liyanage and Liyanage, 1992). Of the perennial grass weeds, Imperata 
cylindrica is the most noxious and troublesome weed not only in coconut 
plantations but also in other crop ecosystems as well (Renaldo et al., 1980). 
37 
This species tolerate shade up to 50% and thrives well under mature 
coconut plantations (Soerjani, 1970). 
Imperata is found abundantly in coconut plantations in Intermediate Dry 
zone of Sri Lanka, particularly in marginal coconut lands with sandy soils. 
The ability of Imperata to thrive well in marginal coconut lands particularly in 
sandy soils, aggravates the problem of weed competition in coconut. This 
emphasizes the importance of eradication of Imperata from coconut lands 
as it is an aggressive, rhizomatus perennial grass, which reproduces 
profusely from both seeds and rhizomes (Mercado, 1986). Of the various 
methods used to control Imperata, impact of repeated slashing and tillage, 
replacement of Imperata with leguminous cover crops and chemical 
methods have been reported by several authors (Mercado, 1986; Liyanage 
and Liyanage, 1992; Renaldo et al., 1980). Although leguminous cover 
cropping has been reported to be the most effective method of controlling 
Imperata (Renaldo et al., 1980), it is difficult to establish leguminous covers 
in coconut lands with sandy soils. This study envisages to find the 
effectiveness of use of several mechanical and chemical means of control 
Imperata and to assess the impact of coconut - Imperata competition on the 
yield of coconut. 
MATERIALS AND METHODS 
The experiment was conducted at Mangalaeliya in Puttlam District in low 
country dry zone of Sri Lanka from 1997 to 2000. Soil at the location was 
sandy and belongs to the great soil group of Sandy Regosols. The mean 
annual rainfall and temperatures were 1492 mm and 23.8-31.5 0 C, 
respectively. Following treatments were imposed. 
T1 - Harrowing with disc harrow 
T2 - Application of Glyphosate 2.88 kg, a.i. / ha 
T3 - Application of Glyphosate 1.44 kg, a.i. / ha 
T4 - Circle weeding with application of Glyphosate (1.44 kg, a.i. / ha) 
and slashing the rest of the area 
T5 - Mechanical slashing of Imperata 
T6 - Unweeded (control) 
The experiment was laid in a randomized complete block design with three 
replicates. Each plot comprised of six effective palms of around thirty years. 
Slashing was done with a tractor-mounted rotary slasher while harrowing 
was done to a depth of 15 cm using tractor mounted disc- harrow. Spraying 
of weedicide was done with a knapsack sprayer. Treatments were imposed 
twice a year in six monthly intervals. Weed biomass was ascertained by 
quadrate sampling (0.5m 2 quadrate) followed by oven drying at 105 °C for 
38 
24 hrs. Harvesting of coconut palms in each plot was done at two monthly 
intervals. Total yield for a year was obtained from all six palms. 
B/C ratio was used to determine the cost effectiveness of different Imperata 
control methods. Benefits were calculated as the average incremental yield 
per year over the Imperata uncontrolled, considering the yields of previous 
three years. 
RESULTS AND DISCUSSION 
Effect of different control methods on reduction of shoot biomass of 
Imperata 
Figure 01 illustrates the reduction of biomass of Imperata due to different 
control methods over time. Of the various methods used, slashing in six 
months interval had the least effect on biomass of Imperata. According to 
Sandnam et al., (1977), slashing at shorter intervals, results in better control 
of this weed. However slashing Imperata at shorter intervals in coconut 
lands may not be cost effective. Disc harrowing in six month- interval has 
reduced the biomass of Imperata better than slashing. This is probably due 
to the fragmentation of under ground parts thus, desiccation of the 
rhizomes. Effectiveness of control of Imperata by successive soil cultivation 
has been reported by several authors (Knows and Cole, 1973; Ivens, 1975, 
Mercado, 1986). Martin, (1975), has recommended successive tillage with 
disc harrowing at 8-10 week intervals for better control of Imperata. 
Control of Imperata with Glyphosate( N- Phosphonomethyl glycine) at the 
rate of 2.88 and 1.4 kg a.i /ha (Counter-a.i., 356 g/l) gave a significant 
reduction (P<0.05) of weed biomass when compared to other methods. 
Effectiveness of glypohsate for control of Imperata has been reported by 
several authors (Rognon et al., 1984; Wrong 1971; Golan 1976; Mercado, 
1986; Liyanage et al., 1992). Although an integrated approach i.e. 
application of glyphosate followed by establishment of leguminous creeping 
covers was found to be effective in controlling Imperata (Liyanage et al., 
1992; Renaldo et al., 1980), practical difficulties of establishment of cover 
crops in sandy soils in Low Country Dry Zone in the coconut triangle pave 
the way for the present study to opt for alternative methods of control. 
39 
sr 1 5 0 0 
E 
™ 1200-
S 
g 900 -
Q. E 
•S 600-
I 300 -
o S 0 
1997 1998 1999 2000 
Years 
- A- - - Harrowing (Twice/year) • Gtyphosate( 8 l/ha) — •—Glyphosatef 4 l/ha) 
—H Circle weeding/Slashing — •» - -Slashing (Twice/year) -knperata uncontrolled 
Figurel: Effect of weed control methods on biomass yield of Imperata 
Effect of Imperata on yield of Coconut 
Control of Imperata resulted in a significant increase (P< 0.05) in nut yield 
over the uncontrolled plots even a year after imposition of treatments. 
Impact of Imperata on nut yield was clearly shown after 2 years of treatment 
application, where increase in nut yield was 102% and 49% respectively 
with glyphosate treatments (average of two concentrations) when compared 
to unweeded control in the years 1999 and 2000. When the cumulative yield 
of 3 years were considered, control of Imperata with glyphosate has 
increased the nut yield by 55 %, when compared to the unweeded control. 
Imperata cylindrica is a strong competitor for soil nutrients and moisture 
resulting in poor growth and reduction of nut yield (Renaldo et al., 1980). 
Martin and Mudlier (1983) reported a reduction of copra yield by 14 % due 
to coconut- weed competition in general. However literature on degree of 
competition exerted by Imperata on yield of coconut is scarce. 
Of the rest of the treatments, control of Imperata with harrowing or slashing 
did not contribute for a significant increase in nut yield on yearly basis 
(Tablel). Eighty percent of the root zone of coconut is confined in the 
circular area with in the radius of 2m from the coconut boll (Liyanage, 1985), 
which is referred to as "manure circle". It is expected to keep the manure 
circle free from weeds to reduce the coconut-weed competition. However 
the present study showed that weeding in the manure circle with glyphosate 
has not significantly reduced the coconut- weed competition (Fig. 2) in the 
case of Imperata infestation. 
40 
Table 1: Effect of different control methods of Imperata on yield of coconut 
Treatments Year 
1997 1998 1999 2000 Cumulative average 
yield per palm1 
Harrowing 31 43 56 56 52(18) 
Glyphosate 2.88 27 45 88 72 69(56) 
kgs, a.i. / ha 
Glyphosate 1.44 32 54 82 65 67(52) 
kgs, a.i. / ha 
Circle weeding 33 35 56 57 51(16) 
with Glyphosate 
Slahing 33 45 60 55 53(20) 
Unweeded 35 45 42 46 44 
control 
Significance NS * ** * ** 
C V % 10 16 13 7 
LSD 9 19 14 8 
NB. Values were rounded to the nearest digit. 
'Cumulative annual average yield for year 1998,1999 and 2000 
* = Significance at 5 %,** = Significance at 1% , NS = Not significant 
Values in parentheses are the percentage increase of nut yield over the control 
Cost/Benefit analysis of control methods of Imperata 
Table 2 : Costs and benefits of different control methods of Imperata 
Method of Costs* Average Incremental Undiscounted 
control (Rs/ha/ annual benefits (Rs.)^ B/C ratio 
annum) incremental @ Rs.9.00/nut 
yield/ha 
Harrowing 6000.00 1280 11520.00 1.92 
Application of 
Glyphosate 2.88 9600.00 4000 36000.00 3.75 
kgs, a.i. / ha • 
Application of 
Glyphosate 1.44 5600.00 3680 33120.00 5.91 
kgs, a.i. / ha 
Circle weeding 
with Glyphosate 9500.00 1120 10080.00 1.06 
and slashing 
Slahing 7500.00 1440 12960.00 1.73 
Values are in Sri Lankan Rupees (I US$= SLR. 102.00) 
* Include material machinery and labour costs for twice a year 
Average price of commercial product of Glyphosate : Rs. 400/liter (360 g a.i./litre) 
Average labour wage: Rs.200/manday 
41 
The costs of different methods of control of Imperata are given in the Table 
2. Although the highest increase of nut yield was achieved in plots treated 
with glyphosate at 2.88 kg of a.i. /ha, the highest returns to investment (B/C 
ratio: 5.9) was given by the plots treated with glyphosate at 1.44kg a.i./ha, 
thus making it the most effective method of control of Imperata among the 
tested treatments. 
CONCLUSION 
Imperata cylindrica is a strong competitor for coconut reducing, the nut yield. 
This study showed that control of Imperata with glyphosate in coconut lands 
with sandy soil in low country dry zone increased the nut yield by 55% when 
compared to that of unweeded plots. Application of glyphosate at the rate of 
1.44 kg a.i (4 litres of commercial mixture; Counter-a.L, 356 g/l) found to be 
cost effective method of controlling Imperata in coconut lands in low country 
dry Zone. 
REFERENCES 
Renaldo G. and San Juan C. (1980). Replacement of 'Cogan" (Imperata 
cylindrica. (I.) Beau, vegetation under coconut with leguminous cover 
crops, The Philippine Journal of COCONUT STUDIES, pp 32- 39 
Liyanage, L.V.K. and Liyanage, M.de.S (1992). Weed control- Understory 
weed management in coconut lands, CORD (1) viii. pp 48-56. 
Soerjani.M. (1970). Alang-alang, Imperata cylindrica (L.) Beauv. Pattern of 
growth as related to its problem of control, BIOTROP Bull.(1) pp88. 
Beatriz L. Mercado (1986). Control of Imreata cylindrica. In. Weed control in 
Tropical Crops ( Ed. K.Moody ), Vol.ll, Philippines Weed Science 
Society, pp 269-278. 
Sandanum, S. and Jayasinghe, H.D. (1977). Manual and Mechanical 
control of Imperata cylindrica on tea lands in Sri Lanka, PANS 23, pp 
421-426. 
Martin, G. (1975). Land preparation of Imperata savannale or grass pasture, 
Oleagineux 30, pp 467-470. 
Martin, M.P.L.D and Mudaliar, T. (1983). Response of coconut to fertilizer 
application and weed control, Fiji Agric.J.45 (2), pp 51-53. 
42 


Effect of different control methods of imperata cylindrica on Coconut (Cocos nucifera) yield in low country dry zone of Sri Lanka.

Mathes, D.T.

Marikkar,J.M.N

COCOS (2004), 16, 56 - 64 
Printed in Sri Lanka 
THE IMPACT OF HARVESTING COCONUTS 
AT MONTHLY INTERVALS 
D T Mathes and J M N Marikkar 
Coconut Research Institute, Lunuwila. Sri Lanka 
ABSTRACT 
From the time immemorial coconut bunches were harvested at two monthly 
intervals. In general two such bunches are harvested at a given harvest. 
However on the average a coconut bunch matures more or less every 
month. If these could be harvested at monthly intervals without any adverse 
effect on the nuts there will be several benefits. These are availability of 
nuts over the months, savings on mature nut fall which otherwise would 
have lost, steady monthly income to the pickers and thereby reducing the 
risk of extension of skilled pickers. There was however no information 
about the nature of impact monthly harvesting has on the production of 
yield. In order to address on this issue three long term experiments were 
conducted at three different agro climatic zones, to study the impact of 
monthly harvesting on yield as compared to two monthly harvesting. One 
experiment ran over a period of 10 years, while the other two over a period 
of five years. Overall results were promising, by way of, increased nuts, 
quality of copra unaffected, mature nut fall reduced to a bear minimum and 
substantive gain in income to the pickers who play a vital role in the 
production of coconut, for harvesting coconuts at monthly intervals. 
INTRODUCTION 
The Coconut palm being a perennial is a life long crop. From the time of 
planting a seedling, it achieves its full bearing status between 10 to 15 
years under average management conditions. From attaining the bearing 
stage, the coconut palm delivers one mature bunch more or less regularly 
each month. Once a bunch is matured, it is ready to be harvested. By 
retaining such a bunch on the tree any longer will not provide any benefit, 
except that it would be considered as an unwanted bunch by the tree. 
Though a bunch of coconut is ready to be harvested at monthly intervals, 
the farmer however used to harvest the mature nuts at two monthly (60 
day) intervals. This is the tradition practiced from the time immemorial for 
convenience and with the objective of saving on costs. Also there was an 
expressed concern that, harvesting at 30 day intervals would effect the 
quality of copra. 
In general 12 mature bunches are harvested during a given year, six of 
these bunches however remain one month longer than required. On an 
average two bunches are generally harvested when harvesting at 60 day 
intervals. The two bunches are such, one bunch is two months old and the 
other one month old. Hence the argument that harvesting at 30 day 
intervals could effect the quality will not hold much good. 
This paper describes the results of three long term studies which examined 
the overall scope for harvesting mature coconuts at monthly intervals as 
against two monthly intervals. 
MATERIALS AND METHODS 
Experimental site 
The first field experiment was conducted at Walpita Research Centre 
(7.3°N, 80°E) belonging to the Coconut Research Institute. The duration of 
the experiment was from 1991 to 2003. The research centre falls in the wet 
zone of Sri Lanka. The soil was sandy loam. Subsequently two additional 
experiments were established at Ratmalagara and Poththukulama 
Research Centres. Ratmalagara Research Centre (7.5°N, 79.9° E) falls in 
the low country intermediate zone, while Poththukulama Research Centre 
(7.6°N, 79.8°E) falls in the low country dry zone. The soil types of the two 
centers being gravel and sandy loam, respectively. These two experiments 
were commenced simultaneously in 1999 and concluded in 2003. 
Weather Conditions 
The rainfall in all the three stations is bimodal with peaks in April/June and 
October/November. The total rainfall for each year since 1994 to 2003 in 
respect of each research centre is shown in Table I. 
Table 1: Total rainfall in (mm) at the three research centers over the period 
1994 to 2003 
Research centre Total rainfall in mm. 
1994 95 96 97 98 99 2000 01 02 03 
Walpita 1688 2266 1623 2739 2253 2649 2096 1743 2143 2217 
Ratmalagara 1718 1630 1199 2075 1750 2046 1700 1331 1800 1363 
Poththukulama 1286 1834 1195 1767 1649 1637 1499 965 1644 1211 
57 
The average rainfall during the 10 year period for Walpita, Ratmalagara 
and Poththukulama research centers were 2142, 1661 and 1469mm., 
respectively. 
• average copra weight/nut (gm.) at 6% moisture 
• grading of copra (MS-1 in %) 
• copra out turn(nuts/250 kg) 
• coconut oil (g/kg of copra) 
• Free fatty acid (FFA) (as lauric acid in%) 
Results are discussed and presented here 
RESULTS 
Plantation 
The experiments were conducted on an adult plantation. The coconut 
plants were open pollinated tall variety. 
Treatments 
Two frequencies of harvesting, ie. 30 and 60, day intervals were tested at 
Walpita research centre. Three frequencies of harvesting, 30, 60 and 120 
day intervals were tested at the other two research centers. Randomized 
block design was used in all the three experimental sites. There were six 
replicates in each experiment. Each plot constituted 6 palms. 
Observations 
Harvesting was continued throughout the experimental period according to 
the chosen intervals. Number of nuts per each bunch was recorded at 
each harvest. The total yield in respect of each year was first analyzed 
separately. The average over the experimental period was subsequently 
analyzed for each experiment. Records of fallen nuts too were kept. 
Assessing the quality of Copra 
Nuts collected from the experiment at Walpita research centre were used to 
assess the impact of monthly harvesting on copra quality. Copra was 
made in the Ceylon copra kiln. The copra drying was carried out in one 
major chamber in the copra kiln available at Coconut Research Institute 
after seasoning the nuts for 21 days. A wooden box subdivided into 40 
apartments was used for curing split nut samples. Each sample contained 
8 nuts. Twelve drying cycles were done over the period, October 1998 to 
58 
August 2000. The quality of copra was thus assessed over a two year 
period. 
Quality of copra was assessed using the parameters 
Effect of frequency of harvesting on the yield 
Walpita Research Centre 
Numbers of nuts per tree recorded over the period in relation to harvesting 
frequencies are shown in Table 2. 
Table 2: Effect of Frequency of harvesting on number of nuts per tree 
Harvesting 
frequency 
Year Aver 
age 
91 93 94 95 96 97 98 99 00 01 02 03 94-03 
30rJay 117.6 51.6 126.4 98.8 87.5 107.8 93.8 106.2 98.3 92.7 72.3 73.4 95.7 
60 day 112.2 48.5 94.2 80.7 75.3 90.1 67.8 72.9 78.1 66.4 55.9 50.1 73.1 
Significance ns ns 0.001 0.01 0.05 0.05 0.001 0.01 0.01 0.001 0.01 0.001 0.001 
(P=> 
CV% 12.2 11.9 12.3 13.6 10.6 16.6 11.7 12.7 13.4 15.5 12.7 
When the experiment was commenced in 1991, nuts per tree indicated no 
difference between the yields of the two treatments. No significant 
difference was also shown between the two treatments for thayear 1993 as 
well. From 1994 onwards, all the years showed significantly." higher yields 
for 30 day harvesting as against 60 day harvesting. The yields for 60 day 
harvesting indicate the general pattern of harvesting at two monthly 
intervals. The yields for 30 day harvesting indicate the kind of additional 
yields that were observed when harvested at monthly intervals. The 
average yield for the year 1994 to 2003 showed 22.6 more nuts per year for 
30 day harvesting compared to 60 day harvesting. This is a 30.9% yield 
increase. 
Ratmalagara Research Centre 
The effect of frequency of harvesting on the yield is shown in Table 3. 
59 
Table 3: Effect of frequencies of harvesting on number of nuts per tree 
Harvesting frequency Year Average 
1999 2000 2001 2002 2003 (2000-2003) 
30 day 96.1 85.6 92.0 74.4 74.4 81.5 
60 day 83.5 65.5 74.8 64.5 61.6 66.6 
120 day 90.5 60.4 67.5 63.8 63.7 63.8 
Significance(p=) ns 0.01 0.01 0.05 0.05 0.05 
CV(%) 7.5 9.5 11.3 9.8 10.4 9.7 
As could be expected the commencement year (1999) did not show any 
significant difference between the treatments. During the period 2000 to 
2003 harvesting frequencies showed significant difference between the 
treatments. The significant difference was observed for harvesting at 30 
day intervals as against the other too harvesting intervals. Harvesting at 60 
day and 120 day did not show a significant difference between the two 
treatments. The analysis for the average yields (2000 to 2003) showed 
significantly 14.9 more nuts per tree for harvesting at 30 day intervals as 
against 60 day harvesting. This is a 22.4% yield increase. 
Poththukulama Research Centre 
The results indicate similar pattern as that shown for the experiment 
conducted at Ratmalagara research centre. The yields for 30 day 
harvesting showed significantly higher yields when compared to rest of the 
two treatments, with no appreciable difference between harvesting at 60 
and 120 day intervals. The results are described in Table 4. 
Table 4: Effect of frequencies of harvesting on number of nuts per tree 
Harvesting Year Average 
frequency 1999 2000 2001 2002 2003 (2000 - 2003 
30 day 109.3 96.6 97.6 79.3 97.1 94.1 
60 day 106.4 80.2 84.3 68.4 85.0 86.2 
120 day 110.7 58.4 77.6 64.1 80.9 80.0 
Significance^) ns 0.001 0.05 0.05 0.05 0.05 
CV(%) 6.6 8.9 11.0 13.1 9.3 7.1 
Analysis of average yields (2000 to 2003) showed significantly 7.9 more 
nuts per tree for harvesting at 30 day intervals as against 60 day intervals. 
This is a 9.2% yield increase. 
Quality of Copra 
Measured using parameters; copra (wt/nut), Grade of copra, copra 
out - turn and coconut oil 
The average values of parameters measuring the quality of copra for the 
two frequencies of harvesting, monthly and bimonthly are shown in Table 5. 
The values show that in some instances the average copra weight is 
slightly high for nuts harvested at monthly intervals, while low in other 
instances. The over all results suggest that there is no evidence to say 
copra yield is better for nuts harvested at monthly intervals as against for 
nuts harvested at bi-monthly intervals. When considering the period Oct 
98 to Aug. 99 the average copra wt/nut for monthly harvesting is 189 gm 
while for bimonthly harvesting it is 198 gm. During the period Oct-99 to 
Aug 2000 the respective values were 207 and 197 gm. Considering the two 
time periods together, the overall average is 198 and 195 g., respectively. 
Similar arguments could be met in respect of grade of copra, copra outturn 
(nuts/250kg of copra) and coconut oil (g/kg of copra). 
Measured using the parameter; free fatty acid (FFA) 
FFA is an important parameter in assessing the quality of copra. For good 
quality copra, the FFA value should be less than 1 % . Lower the better. 
The values shown in Table 5 indicate very low values of FFA in respect of 
nuts harvested at both the intervals. The foregoing results indicate that 
there is no difference in quality of copra produced using nuts harvested at 
monthly or bimonthly intervals. 
DISCUSSION 
A coconut palm, from coming into bearing, continues to produce nuts over 
a period of 50 years or so. The axil of each frond carries an inflorescence. 
From the stage of primodium of inflorescence, a bunch goes through a 
development cycle of around 44 months before being harvested as a 
mature bunch. An inflorescence once opened, takes on an average 12 
months before it is ripe and ready to be harvested. The nuts produced is 
the most important commodity of a coconut palm. The yield status of a 
palm is generally identified according to the number of mature nuts it 
produces over a period of one year. A palm providing more than 75 nuts 
per year is considered to be a good yielding palm, which amounts<3r?250 
nuts/ha/yr. 
The yield of a palm is however subject to fluctuations in relation to variation 
in weather. Thus any response, due to an external stimulant to increase 
yields, has to be looked into with the above explained background in mind. 
On reaching maturity, nuts have to be harvested, if otherwise these will 
start falling after some time. These nuts are collected as fallen mature 
nuts. It is frequently complained that these nuts are lost by way of thieving. 
Higher the number fallen, larger would be the lost. 
61 
From the time immemorial nuts were harvested at two monthly intervals. 
However on the average nuts reach maturity stage after a month or so from 
opening, which are thus ready to be harvested. 
The three experiments described in this paper were designed to study the 
nature of impact, harvesting at 30 day intervals, will have on the yield of a 
palm as compared to harvesting at 60 day intervals. The three experiments 
showed clear evidence of increased yields when nuts are harvested at 
monthly intervals. The increases were evident for all the years, during the 
period the experiments were conducted. Walpita research center which 
falls in the wet zone showed an average increase of 30%. The respective 
average yields for Ratmalagara and Poththukulama, research centers were 
22.4% and 9.2%. The results seem to suggest that the level of percentage 
increase in yield for monthly harvesting is also dependent on the climatic 
conditions. 
Abeywardna and Mathes (1971) reported that 2/3of button nuts fall during 
the first four months of opening an inflorescence. According to them the 
loss is in the range of 120 button nuts per year. Thus the increases 
observed in the experiment are marginal and could even be considered as 
retention of falling of button nuts. 
Financial benefits 
Harvesting at 30 day intervals involves additional 6 harvests being done 
during an year. This will result additional expenditure on harvesting and 
other activities. The expenditure is about twice as much as harvesting at 
60 day intervals. Thus acceptance of harvesting at 30 day intervals would 
largely depend on the additional income a farmer would derive. It is 
expected to present here the income that could be derived considering a 
marginal increase in yield for a farm producing a yield of 8750 nuts/ha/yr 
where harvesting is done at two monthly intervals. For example consider a 
marginal yield increase of 10% by adopting harvesting at monthly intervals. 
The absolute yield increase = 875 nuts/ha/yr. This increase is a mere 6 
nuts/tree/yr or 6 nuts/12 bunches/yr. 
The additional expenditure (per ha) that would be incurred for adopting 
harvesting at monthly intervals is as follows. 
* picking extra 6 picks @ Rs. 1.25/per palm = Rs. 1125.00 
* collecting 875 nuts @Rs. 200/per 1000 nuts = Rs. 175.00 
* cart hire to transport 875 nuts 
@Rs. 200/- per 1000 nuts = Rs. 175.00 
Total additional expenditure = Rs. 1475.00 
Net income is calculated at different price levels of a coconut and shown in 
Table 6. 
62 
Table 6: Net gain in income (Rs. per ha per yr) 
Price per nut Rs. Additional Net income per ha The ratio of income 
expenditure per/ha/yr per year Rs. per unit additional 
Rs. expenditure 
7.00 4650 1:3.1 
8.00 5525 1:3.7 
9.00 1475.00 6400 1:4.3 
10.00 7275 1:4.9 
11.00 8150 1:5.5 
12.00 10,500 1:7.1 
The results indicate the nature of financial benefits that could be achieved 
by a change to monthly harvesting. As the price of a coconut increases the 
net gain increases. At the price of Rs. 7 a nut, the net gain is 3.1 times per 
unit investment. And at Rs. 12 a nut, it is 7.1 times per unit investment. 
The results shown should be convincing for a farmer to decide on a 
change in respect of harvesting coconuts. 
Extent of mature fallen nuts 
Once a bunch is matured it is ready to be harvested. However if such a 
bunch is kept in the tree longer, the scars get dried and the nuts start 
falling. These nuts are usable nuts. The fallen nuts have to be collected 
regularly, if otherwise there could be losses by way of thieving. The 
number of fallen nuts is much high, for harvesting at 60 day intervals. This 
position is shown in Table 7. 
Table 7 : Matured fallen nuts (%) at the three research centers 
Frequency Walpita Research Ratmalagara research Poththukulama 
of harvesting Centre Center Research Center 
Range Ave. % Range % Ave. % Range % Ave. % 
% 
Monthly 2.5-19.3 9.9 1.6-4.4 2.9 1.1-2.4 1.6 
Two monthly 8.3-35.6 , 23.7 4.5-17.2 12.6 9.9-11.3 10.7 
There is substantial reduction in mature nut fall due to harvesting at 
monthly intervals. This offers two - fold benefits, 
• less effort and time is required to collect fallen nuts. If at all 
such may not be necessary, because these are collected at 
the harvest. 
• will reduce or stop losses due to possible theft. 
63 
1» 
Steady monthly income to pickers 
The coconuts are harvested by coconut pickers. Thus their services are 
very valuable and should be recognized. Without the coconut picker, there 
is no way of harvesting nuts. Coconut pickers thus play a vital role in the 
process of harvesting nuts. Hence it is important that their living standard 
be improved by providing at least a good steady monthly income. The 
additional expenditure involved is very minimal as shown priori. The 
benefits however to the farmer are at large. 
CONCLUSION 
This long term nevertheless exploratory experiment, provided information 
as to the nature of overall benefits that is achievable by a farmer and 
pickers, by harvesting nuts at monthly intervals. The farmer benefited by 
way of increased yields and income. He was also relieved of the 
misconception that monthly harvesting could provide low quality copra. 
The picker benefited by way of increased income or an income twice, as 
much as they could have earned otherwise. Thus all in all there is good 
promise for adopting harvesting at monthly intervals. 
ACKNOWLEDGEMENT 
The authors, especially the senior author wishes to express grateful thanks 
to Mr. Ranjith Fernando, Mr. Leslie Fernando, Mr. Kingsley Fernando, Mr 
Protus Fernando and Mr Chandrasiri Fernando for assisting in maintaining 
the long term field records. Mrs Udula Abesinghe for typing the script. To all 
other officers of the Biometry division who assisted in some way or the 
other in bringing out this fruitful results presented in this paper. Finally to all 
scientists of the Coconut Research Institute who provided valuable 
observations at different times. It was very gracious of them all. 
REFERENCE 
Abeywardena, V. and Mathes, D.T. (1971). Crop losses in coconut through 
button shedding and immature nut fall. CCPR. 6, 97-106. 
64 


The impact of harvesting coconuts at monthly intervals

Zoysa, A.K.N.

Mohamed, M.T.Z.

Proceedings of the first symposium on plantation crop research : "Current trends and future challenges"

Fernando, S.C.

Weerakoon, L.K.

Gunathilake, R.

COCOS (2004), 16, 01 - 10 
Printed in Sri Lanka 
MICROPROPAGATION OF COCONUT THROUGH 
PLUMULE CULTURE 
S C Fernando, L K Weerakoon and T R Gunathilake 
Coconut Research Institute, Lunuwila, Sh Lanka 
ABSTRACT 
Plumule tissues have found to be more responsive explants for clonal 
propagation of coconut. In the present study, the feasibility of using plumule 
explants for clonal propagation of a local coconut variety (Sri Lanka Tall) 
was assessed. Plumules were cultured in three basal media (MS, Y3 and 
72) supplemented with 2,4-dichlorophenoxyacetic acid (2,4-D) (24 - 400 uM) 
and activated charcoal. Somatic embryogenesis and plant regeneration 
were induced by incorporating of abscisic acid (ABA) into the medium. 
Attempts were made to improve plant regeneration by applying high agar 
concentration-induced water stress, cytokinin or silver nitrate in combination 
with ABA. 
The results revealed that callus can be initiated from plumule explants 
cultured in all three basal media tested. The callus formation depended on 
the concentration of 2,4-D in the media and the best effect was observed 
with the lower level (24 uM) tested. The plant regeneration frequency 
observed with ABA treatment was 4.4 %. The combination of ABA with high 
agar concentration-induced water stress doubled the plant regeneration 
frequency. About 50 % of the regenerated plants could be successfully 
acclimatized and field planted. 
The results of the study indicate the possibility of regenerating plants from 
plumule explants of coconut. The method can be used for multiplication of 
improved seed material. However, the plant regeneration efficiency should 
be further improved for mass scale propagation of coconut using plumule 
explants. 
INTRODUCTION 
The coconut palm is a major plantation crop and the most important palm of 
the tropics. Due to its economic importance, breeding for crop improvement 
is of high priority. Coconut is a cross-pollinated and heterozygous plant, 
which is so far, propagated exclusively through seeds. Clonal propagation of 
coconut is of prime importance for rapid multiplication and distribution of the 
best genotypes obtained through conventional breeding. Furthermore, it 
1 
would also allow rapid m< Implication of selected parental palms for 
establishing seed gardens and selected individuals, exhibiting resistance to 
biotic and/ or abiotic stresses, for increasing the yield. 
Initial attempts have been made to micropropagate coconut through 
different explants such as immature inflorescence (Branton and Blake, 
1983), tender leaf (Raju et al., 1984) and immature zygotic embryo 
(Karunaratne and Periyapperuma, 1989). Later studies by Hornung (1995) 
and Chan et al. (1998) have shown that the response of plumules (embryo 
meristem and first leaves) to in vitro culture conditions is better than that of 
other tissues. Therefore, plumules could be used as a model for clonal 
propagation of coconut. As plumules are excised from zygotic embryos, they 
can only produce clones of palms with unknown performance. However, if 
the embryos are obtained by controlled pollination of selected parents, the 
clones from these embryos are likely to show many of the desired 
characteristics of the parent palms (Chan er al., 1998). 
This paper reports the progress of clonal plant regeneration of a local 
coconut variety (Sri Lanka Tall) using plumule explant. 
MATERIALS AND METHODS 
Plant material 
Mature nuts (12-14 month-old) of the variety Sri Lanka Tall coconut were 
used as the source of mature zygotic embryos. 
Callogenesis 
Mature embryos were cultured in modified Eeuwens Y3 liquid medium 
(supplemented with 0.1 uM 2,4-D, 5 uM 6-benzylaminopurine (BAP), 6 % 
(w/v) sucrose and 0.25 % (w/v) activated charcoal [Fluka]), optimized for 
mature zygotic embryo culture of coconut (Weerakoon er al., 2002). After 
incubation in dark (at 30 + 1 °C) for 15-17 days, plumules were excised from 
these embryos (Fig. 1a). They were crushed and cultured in 28 ml screw 
capped vials containing 10 ml of culture medium. The effect of three basal 
media [medium 72 supplemented with 24 uM 2,4-D ( Karunaratne and 
2 
Figure 1: Plant regeneration from plumule explants of coconut, a - Mature 
zygotic embryo (pre-cultured in germination medium for 15 days) 
ready for plumule excision; b - Callus derived from a plumule 
explant; c - Shoots regenerated from plumule-derived callus; 
d - Field-planted plumule callus-derived coconut plant. 
3 
Periyapperuma, 1989), MS (Murashige and Skoog, 1962) supplemented 
with 400 uM 2,4-D (Hornung, 1995) and Y3 (Eeuwens, 1978) supplemented 
with 100 uM 2,4-D (Chan et al., 1998)] on callogenesis was tested. The 2,4-
D concentrations used were based on previous expe^/nents. All the media 
were solidified with 0.8 % (w/v) agar (Park Scientifk-riand supplemented with 
0.25 % (w/v) activated charcoal (Pharmacos). Cultures were incubated at 30 
± 1 °C for 10 weeks in the dark. Callogenesis was repeated four times each 
time with 15 replicates. 
Somatic embryogenesis and plant regeneration 
Embryogenic callus initiated from plumules cultured in medium 72 
supplemented with 24 uM 2,4-D was used. Callus separated from the 
original explants, was subcultured in medium 72 supplemented with 16 \M 
2,4-D for 4 weeks before transferring to somatic embryoNnduction medium. 
Somatic embryogenesis was induced by subculturing of callus in medium 72 
supplemented with 5 uM abscisic acid (ABA) (filter-sterilized) and 6 % (w/v) 
sucrose for 5 weeks. Maturation of somatic embryos was achieved by 
transferring them to medium 72 (devoid of hormones) for 4 weeks. Somatic 
embryo germination was achieved in Y3 solid medium. Regenerated shoots 
were maintained in Y3 solid for 4-6 months by subculturing at 4-weekly 
intervals (Fernando and Gamage, 2000). During somatic embryo induction, 
cultures were maintained in screw-capped vials containing 10 ml of media 
supplemented with 0.8 % (w/v) agar and 0.25 % (w/v) activated charcoal 
(Pharmacos) whereas during somatic embryo maturation and germination, 
they were maintained in 100 ml flasks containing 50 ml of media 
supplemented with 0.8 % (w/v) agar and 0.25 % (w/v) activated charcoal 
(Fluka). Cultures were maintained at 30 ± 1 °C in the dark. Regenerated 
shoots were maintained at 16-h photoperiod (intensity 17 umol m"2 s'2) until 
they were ready for transferring to ex vitro. If necessary, roots were induced 
on shoots by a pulse treatment of 500 uM indole acetic acid (IAA) as 
described by Fernando and Gamage (1994-1995). 
In the present study, attempts were made to improve plant regeneration 
frequency by testing the effect of high agar concentration-induced water 
stress (2 % agar in somatic embryo induction medium during the initial 2-
week period), 5 jiM cytokinin (BAP or isopentyl adenine [2iP]) and 1-10 uM 
AgN03 in combination with ABA. The experiments were repeated at least 
three times with 30 replicates per treatment. 
Ex vitro establishment of regenerated plants 
The fully developed plants with about three leaves and well-developed root 
systems were de-flasked, rinsed well with water and drenched in a mixture 
of fungicide (0.025 % benlate) and diluted nutrient solution for a few hours 
4 
before transfer to clear polypropylene bags containing sterilized potting 
mixture (river sand and compost 1:1) moistened with a diluted nutrient 
solution. The bags were initially kept sealed (for maintaining high humidity) 
in the glass house. After one week, the cover was gradually removed to 
reduce the relative humidity. The plants were watered regularly and a liquid 
fertilizer (Maxicrop™) was sprayed every 10 days. In addition, a solution 
containing minerals of Y 3 medium (Eeuwens, 1978) was applied at two 
weekly intervals. After 6-8 months, plants were repotted in larger polybags 
containing a potting mixture of top soil, compost, river sand, dried cow dung 
and coir dust (2:1:1:1:0.5). The plants were kept in a shade-house for about 
3-4 months before transferring to direct sunlight. During this period, a liquid 
fertilizer (Maxicrop™) was sprayed on to plants at 10-day intervals and 20 g 
of young palm mixture (urea: saphos phosphate: muriate of potash, 2:3:2) 
was applied to each plant at two weekly intervals. After exposure to direct 
sunlight for about 1-2 months, they were ready for field planting. Several 
plants were transferred to field following the recommendations of the 
Coconut Research Institute of Sri Lanka (CRISL). 
Statistical analysis 
Analysis of Variance was carried out to test the differences among 
treatments. 
RESULTS AND DISCUSSION 
Callogenesis 
Coconut somatic embryogenesis usually occurs through a callus phase. 
Therefore, production of embryogenic callus is a prerequisite for successful 
plant regeneration. Among several other factors, the presence of an auxin 
in the medium is critical for successful callogenesis (Auge, 1995). The most 
commonly used auxin in coconut tissue culture media is 2,4-D and its 
concentration depends on the explant and concentration of activated 
charcoal in the culture medium (Verdeil and Buffard-Morel, 1995). In the 
present study, the effect of culture media previously used for plumule culture 
of exogenous coconut varieties [MS supplemented with 400 u.M 2,4-D 
(Hornung, 1995) and Y3 supplemented with 100 u,M 2,4-D (Chan et al., 
1998)] and immature embryo culture of Sri Lankan coconut varieties 
[medium 72 supplemented with 24 uM 2,4-D (Karunaratne and 
Periyapperuma, 1989)] on callogenesis from plumule tissues of Sri Lanka 
Tall coconut was tested. The study was extended to assess the effect of 
medium 72 supplemented with higher level (100 uM) of 2,4-D and media MS 
and Y3 supplemented with lower level (24 \iM) of 2,4-D. 
5 
The results revealed that the callusing frequencies were higher and 
comparable in all the three basal media supplemented with lower (24 uM) 
concentration of 2,4-D. Increase in the concentration of 2,4-D up to 100 or 
400 u.M resulted in a decrease in callusing (Table 1). Despite the statistically 
non-significant decrease in callusing frequency in Y3 supplemented with 
100 uM 2,4-D, callus initiated in high 2,4-D containing media showed a poor 
growth compared to that of lower 2,4-D media. 
Table 1: The effect of different culture media on callogenesis in plumule 
explants of coconut 
Basal medium 2,4-D concentration Callusing frequency 
(uM) (%) 
72 24 55.2 
100 40.9 
MS 24 49.4 
400 35.5 
Y3 24 54.3 
100 46.7 
Significance p<0.05 
CV (%) 17.3 
LSD 12.1 
In this study, callusing frequencies in plumule explants cultured in previously 
published plumule culture media (MS+ 400 uM 2,4-D and Y3+ 100 uM 2,4-
D) were lower (35.5 and 46.7 % respectively) than those reported by 
Hornung (1995) (75 %) and Chan et al. (1998) (60 %) . In the present study, 
the published media were tested with high levels of 2,4-D but without the 
specific type of activated charcoal, which had been used by the relevant 
research groups. Different types of charcoal have different adsorption 
capacities, which results in variations in active auxin concentration in the 
medium. Therefore, the use of high levels of 2,4-D in the presence of 
unspecific type of charcoal could be the reason for the low callusing 
frequencies observed. This was further confirmed by the increase of callus 
production in those media by reducing the concentration of 2,4-D. With 
agreement of the results of this study, Saenz et al. (1999) reported that 
callusing in plumules cultured in medium described by Chan et al. (1998) 
could be increased up to 100 % by using a different type of charcoal. 
Furthermore, the use of different coconut genotypes for studies of different 
research groups might also have contributed to the variable results. 
Somatic embryogenesis and plant regeneration 
Generally, somatic embryogenesis in coconut callus has been induced by 
gradual reduction of auxin concentration with a corresponding increase in 
the cytokinin level in the medium (Buffard-Morel et al., 1995). In contrast, 
6 
somatic embryogenesis in coconut has also been induced by an early 
increase in 2,4-D concentration followed by a gradual reduction (Verdeil et 
al., 1994) or a rapid decrease in 2,4-D concentration and application of high 
concentration of cytokinin (Chan era/., 1998). However, research conducted 
at the CRISL revealed that an alternate treatment, removal of auxin and 
incorporating ABA to the culture medium, give rise to more consistent plant 
regeneration from coconut callus (Fernando and Gamage, 2000). Similarly, 
Samosir et al. (1999) reported improved somatic embryogenesis in coconut 
with the use of ABA. 
In this study, embryogenic callus (Fig. 1b) treated with 5 uM ABA, became 
more compact. After 5 weeks in the medium with ABA, whitish globular 
structures were visible. Upon transfer to the medium devoid of hormones for 
four weeks, some of the embryogenic structures elongated whereas the 
others developed into haustorial tissues or fused shoot-like structures. On 
repeated subculture to the Y 3 medium, the somatic embryos produced 
shoots (Fig. 1c). 
Incorporating ABA to the culture medium resulted in normal development of 
somatic embryos that can develop into complete plants. However, the plant 
regeneration frequency was low (4.4 %) . Among the treatments tested, only 
the application of high agar-induced water stress in combination with ABA 
had a positive effect and it doubled (9.0 %) the plant regeneration frequency 
(Table 2). The use of ABA in combination with osmotically active substances 
has resulted in improved somatic embryogenesis and plant regeneration in 
coconut (Samosir et al., 1999), rubber (Linossier et al., 1997) and several 
other crops. The moisture stress, induced by application of high agar 
concentration in the medium has also shown encouraging results in plant 
regeneration of rice (Jain et al., 1995). The effect of such a stress has not 
been tested for coconut previously. The enhanced results observed in this 
study might be due to promotion of the expression of embryo-specific 
genes, improved embryo development and increased production of storage 
reserves caused by moisture stress. 
Table 2: Effect of high agar concentration - induced water stress on plant 
regeneration 
Treatment Plant regeneration 
(%) 
ABA 4.4 
ABA + high agar-induced water stress 9.0 
Significance P= 0.01 
CV (%) 31.8 
LSD 0.3 
7 
An embryogenic callus clump that regenerated plants produced an average 
number of 1-2 plants. The clonal plants were maintained in Y3 medium until 
they produced 2-3 leaves and a good root system. When shoots did not 
produce roots spontaneously, the application of an IAA pulse resulted in 
successful rhyzogenesis in more than 90 % of the treated shoots. When the 
complete plants were transferred to the potting medium for acclimatization, 
about 50 % of plants survived and they could be transferred to field 
successfully (fig. Id). 
The results of.this study indicated the possibility of regenerating clonal 
plants of the local variety Sri Lanka Tall using plumule explants. The 
concentration of 2,4-D in the callusing medium was found to be the critical 
factor determining success in callogenesis. Application of ABA in 
combination with high agar level-induced water stress improved plant 
regeneration frequency. The resulting plants could be acclimatized and field 
planted successfully. This method can be applied for multiplication of 
improved seed material. However, the plant regeneration efficiency of the 
current protocol should be further improved for mass scale propagation of 
coconut using plumule explants. 
ACKNOWLEDGEMENTS 
The authors wish to thank the staff of the Tissue Culture Division for their 
assistance in carrying out the experiments. 
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Micropropagation of coconut through plumule culture

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