S.L.J. Tea Sci. 67(1/2), 54-66, 2002, Printed in Sri Lanka 
CHARACTERIZATION OF SOILS I N T H E T E A G R O W I N G REGIONS OF 
S R I L A N K A I N R E L A T I O N TO POTASSIUM D Y N A M I C S 
G.R Gunaratne and L.S.K. Hettiarachchi 
(Tea Research Institute of Sri Lanka, Talawakelle, Sri Lanka) 
and 
A.N. Jayakody 
(Faculty of Agriculture, University of Peradeniya, Peradeniya Sri Lanka) 
Soils from the six tea growing regions of Sri Lanka namely Ratnapura, Hantane, 
Talawakelle, Kottawa, Deniyaya and Passara under different agio ecological regions 
were collected for this study, and quantity (Q) and intensity (I) measurements 
have been used as a tool for characterization. 
Tea soils used could be characterized into two main groups according to 
their Potential Buffering Capacities of K (PBCk). First group consisting of higher 
PBCk values having constant availability of K over a longer period and second 
group having lower PBCk values which need frequent fertilizations. Sub-divisions 
of soils were also suggested related to presence of K-specific-sites, available 
K as well. 
Q/I isotherms indicated the presence of some specific sites for K ions in 
Ratnapura, Hantane and Talawakelle as against the other 3 soils. 
Finally soils in the tea growing regions were characterized into five groups 
according to their K dynamics. It is worthy to consider these groupings also 
in arriving at K-recommendations for tea in Sri Lanka. 
I N T R O D U C T I O N 
Nutrient availability depends on the nutrients concentration of the soil solution 
at any given time, but also on the ability of the soil to maintain its nutrient concentration. 
This capability of a soil to buffer the nutrient concentration of the soil solution 
is an important factor, as far as nutrient availability is concerned. Therefore, two 
nutrient components in the soil can be distinguished. The quantity factor (Q) represents 
the amount of available nutrients, whereas the intensity factor (I) reflects the strength 
of retention by which the nutrient is held in the soil. Simply, the intensity factor 
is the concentration of the nutrients in the solution. 
5 4 
The concept of nutrient intensity and quantity was first proposed by Schofield 
and Tayler (1955). Beckett (1964a, b) suggested that the intensity of a nutrient 
in soil at equilibrium with its soil solution should be considered as the activity ratio 
(AR). Where, AR k is the activity ratio of K and a K + , a C a : + , a^ 2 * are activities of 
K +, C a : + and M g : + respectively. 
AR" = 
This, AR k has often been used as a measure of K + availability. Tinker (1964) 
pointed out for acid soils, A P should also be considered instead of Ca 2 + and Mg-+, 
as A P is a dominant ion in acid soils. Hence, activity ratio is expressed as follows, 
where a A , 3 + is the activity of Al 3 + . 
AR k = 
( 0 1 / 3 
However, for acid soils that have received dolomitic limestone for a long period, 
combination of the activities of Ca 2 + , Mg : + and Al 3 + is more appropriate (Tinker, 
1964). 
AR" = 
( a c ; - + + % 2 + ) 1 / 2 + ( a A 1 3 + ) 
For construction of a typical Q/I curve, a soil should be equilibrated with 
solutions containing a constant amounts of A1C13 and increasing amounts of KC1 
(Tinker, 1964). Soil gains and losses of K to achieve its characteristic AR k value, 
or remains unchanged if its AR k values are same as the equilibrating solution. The 
ARk values should then be plotted viz. the gain or loss of K (AK) to form the 
characteristic Q/I curve (Fig. 1). From the Q/I plot, several parameters can be 
obtained in order to characterize the K status of the soil. 
The AR k value, when the Q factor or AK equals to zero is a measure of 
the degree of K + availability at equilibrium, or AR k e . Successive cropping decreases 
AR k e values until a constant value is reached (Le Roux, 1966). AR k e does not 
show capacity of a soil to release K + to plants, as soils can have the same AR k e 
value but contain different amount of labile K. 
5 5 
Fig. 1: Typical quantity/intensity (Q/I) plot 
(Sparks and Liebhardt, 1981) 
The value of AK when AR k = 0 is a measure of labile or exchangeable K in 
soils (AK°). Le Roux (1966) noted that AK° was a better estimate of soil labile K 
than normal exchangeable K. He found that higher values of labile K (AK °) indicated 
a greater K + release into soil solution. Sparks and Liebhardt (1981) found that the 
values of AK° compared favorably with NH4OAC-extractable K in the Ap horizon 
of a Kalmia soil. AK° was poorly correlated with plant K uptake by the regression. 
The slope of the linear portion of the curve gives the Potential Buffering 
Capacity (PBCk), and indicates the ability of a soil to maintain the intensity of 
K + in the soil solution and is proportional to cation exchange capacity (C.E.C) 
(Lee, 1973). Le Roux (1966) noted that a high value of (PBCk) is indicative of 
constant availability of K in the soil over a long period of time, whereas a low 
(PBCk) soii would suggest the need for frequent fertilization. 
The number of specific sites for K (K^ is the difference between the intercept 
of curved and linear portion of the Q/I plot at AR k = 0 (Beckett, 1964b). Sparks 
and Liebhardt (1981) found that K^ values in soils tend to increase with increasing 
K fertilization and liming. 
The present fertilizer recommendation in the tea plantations in Sri Lanka is 
mainly based on crop removal but K dynamics of respective soils are not taken 
into account. (Anon, 2000). Thus regional specific fertilizer recommendations may 
be needed to improve the efficiency of soil applied K. For development of such 
56 
procedure, it is absolutely necessary to understand the K dynamics of respective 
soils. Therefore, the main objective of this study was to characterize the soils in 
the tea growing areas in relation to K dynamics. 
MATERIALS AND METHODS 
Sampling procedure 
Six tea growing regions were selected to represent a range of clay mineralogy 
expected to affect cation release and from each region one tea estate were selected 
randomly for sampling. The description related to the soils, are given in Table 1. 
From each estate one field were selected randomly for sampling and from each 
field 40 - 50 cores were collected from depth 0-15cm and 15-30cm separately 
by using post-hole auger. After compositing the collected soils from each field, 
small portion was taken to provide a sub sample of half kilogram. The soil sampling 
were done after a minimum period of six weeks following the last application of 
fertilizer. The moist soils were air dried and passed through a 2mm sieve prior 
to analysis. 
Table 1: Description of the soil used 
Location Great soil 
group 
Soil series Clay mineralogy* Clay 
% 
Organic 
carbon % 
Exch.K 
(mg/kg) 
Exch. Al 
(mg/kg) 
Hantane R.B.L Kandy WhlH " 4 
gbTqTgot 
33 1.69 88 241 
Talawakelle R.Y.P Mattakelle v/cTI k/hlj 
gbTqTgoT k-ft 
P-ft 
28 3.58 116 407 
Ratnapura R.Y.P Malaboda k/hhj v/c* 
gnTqtgoT p-ft 
22 1.25 62 161 
Kottawa R.Y.P Dodangoda k/hrfl v/c$ 
ghtqT 
17 1.33 60 166 
Deniyaya R.Y.P Weddagala k/hlH v /cj 
ghtqTgot 
34 1.50 68 101 
Passara R.Y.P Mahawala-
tenna 
k/hlfl vlct 
ghTqtgoT K-ft 
P-ft 
22 1.29 65 169 
R.B.L- Reddish Brown Latasolic soil 
R.Y.P- Red Yellow Podzolic soil 
v/c-Vermiculite/Chlorite, k/hl-Kaolinite/Hollosite, m-Mica, go-Goethite, q-Quartz, gh-gibbsite, 
k-f-Potassium feldspar, p-f-Plagioclase feldspar 
^-Dominant t- Abundant or co dominant f-Sub ordinate 
* Wimaladasa (1989) 
5 7 
Analytical procedure 
Q/I - relationship using 0.01M A1C13, as the equilibrate 
The Q/I relationship were plotted with data received by equilibrating 5.0 g 
soils with 50.0cm 3 of 0.01 M A1C13 solution containing KC1 from 0.0005 to 0.003 
M, and with 0.01 M A1C13 solution containing no K at soil:solution ratios from 
1:10 to 1:250 in an end-over-end shaker (40 r.p.m.) at 22°C ± 2. After equilibration 
the suspensions were centrifuged at 1600 r.p.m for 15 minutes and filtered through 
whatman No. 42 filter paper to avoid contamination from fine clay material (Sinclair, 
1979; Wimaladasa and Sinclair, 1988). The K concentrations of the clear supernatant 
solutions and the unreacted solutions were determined by flame photometry and 
the change in soil K was calculated. Concentration of (Ca + Mg) were determined 
by EDTA titrametric method (Heald, 1965). Aluminium was determined colorimetrically 
(Jayman and Sivasubramanium, 1974). The electrical conductivity of the supernatants 
were also measured using a conductivity meter. The K activity ratios (ARk) for 
these soils were calculated by equation of Tinker (1964) as given below. 
Tinkers equation for Q/I relationship (Tinker, 1964) 
AR k = 
+ 
K 
(Yo,:+ + Y M 8 2 + ) , / 2 + (Ya , 3 + ) 1 / 3 (cy+ + c M g * r - + (cjy» 
Where a = Ionic activity 
yl = activity coefficient of the i* ion 
i = ( K ^ C a ^ M g ^ a n d A P ) 
C = Concentration of the i* ion in supernatant (mol dm"3) 
Logvi = - 0.509*Zi* (pr- - 0.31) 
1 +I>* 
I = 0.0131X 
Where Zi = valency of the i* ion 
I = ionic strength 
X = Electrical conductivity of the supernatant, (m.mhos cm 2 = ms) 
5 8 
The concentration of Ca and Mg in the 0.01M A1C13 solution were low and the 
desorption part Ca and Mg were undetectable. Therefore, (a^ 2* + a ^ ^ w e r e lower 
when compared with the (a^ 3* ) I / 3 and the units for AR k were considered as M 2 7 3 . 
RESULTS AND DISCUSSION 
Q/I relationship of soils in the different tea growing regions 
The higher initial PBC k values were observed in Deniyaya, Talawakelle and 
Hantane Soils as 6.66, 6.66, 6.15 x lOfag kg 'M " M respectively, when compared 
the Passara, Ratnapura, Kottawa Soils which showed values of 4.50, 3.50, 3.80 
x 104 mg kg "' M 2 / 3 respectively (Figs. 2-7 and Table 2). It can be attributed 
by the higher clay and organic carbon content as there is a close relationship between 
PBC k and the nature of the colloidal complex (Sinclair, 1979). Lee (1973) also 
showed that PBC k is directly proportional to C.E.C of soil. Therefore, soils in the 
tea growing regions can be characterized into 2 main groups according to their 
potential buffering capacities. First soil Group consisting of higher PBC k values 
such as Hantane, Deniyaya and Talawakelle which showed constant availabilities 
of K + over a longer period of time. The 2nd group consisting of lower PBC k 
values such as Passara, Ratnapura and Kottawa may need frequent fertilization. 
Initial AR k e values of Talawakelle, Hantane, Deniyaya and Passara soils were 
23, 17, 22 and 19 x 10 -1 M 2 / 3 respectively. There were considerably higher AR k e 
values when compared with the other two soils namely Kottawa and Ratnapura 
soils which had values of 8 and 12 x 10 ~* M 2 / 3 respectively. This could be attributed 
to higher initial labile K values of former 4 soils, or lower initial K values of latter 
2 soils. Therefore, AR k e cannot be used as a tool for characterization of soils. 
Ie Roux (1966) showed that different soils having the same AR k e do not have 
the same capacity for maintaining the AR k e while K is being removed by plant 
roots. 
The labile K (AK°) values were higher in Passara, Hantane, Deniyaya and 
Talawakelle indicating 80, 100, 130 and 160, mg kg"1 respectively when compared 
to Ratnapura and Kottawa of 40 and 30 mg kg"1 respectively (Table 2). Wimaladasa 
(1989) showed that the calculated AK° values were much lower than the neutral 
1M NH 4OAC extractable K. However contradictory results were observed here 
as there is no consistent differences between AK° and exchangeable K values. 
The curve portion of the Q/I isotherms indicates the presence of some specific 
sites for K-ions. The significance of taking presence of specific sites for K for 
this characterization is, that the K held in the ion exchange complex would be 
dependent on content and type of clay, organic matter, and pH. Exchangeable A P 
which in acid tropical and sub tropical soils can be present in higher concentration 
59 
Table 2: Quantity/Intensity (Q/I) Isotherms Parameters 
Location Depth AR k e AK° PBC* K x 
mgkg" 1 m g k g _ 1 M - 2 / 3 mgkg" 1 
(X10-4) (xlO4) 
Hantane 0-15cm 17 100 6.15 1200 
15-30cm 9 40 7.61 600 
Ratnapura 0-15cm 12 40 3.52 1200 
15-30cm 8 30 3.72 530 
Talawakelle 0-15cm 23 160 6.66 2020 
15-30cm 8 40 5.21 1040 
Kottawa 0-15cm 9 30 3.80 630 
15-30cm 4.5 20 4.28 380 
Deniyaya 0-15cm 22 130 6.66 530 
15-30cm 10 40 5.00 580 
Passara 0-15cm 19 80 4.50 340 
15-30cm 16 70 4.61 530 
than the other cations, compete with K + for non specific sites of exchangeable 
sites of exchange (Tinker, 1964; and SivasubrarnaniumandTalibudeen, 1972). Ratnapura, 
Hantane and Talawakelle soils had more K specific sites in the order of 1200, 
1200 and 2020 mg kgrespectively, when compared with the other 3 soils, Passara, 
Deniyaya and Kottawa soils had 340, 530 and 630 mg kg'1 respectively. This sites 
may be due to the extremely weathered minerals and traces of micaceous minerals 
that present in these soils (Arkoll et al., 1985), but were not detected in the Sri 
Lankan soils by X-ray diffractrometry, except in Hantane. As this was further supported 
by mineralogical analyses reported by Wimaladasa (1989). 
Finally, considering overall Q/I parameters, soils in the tea growing regions 
can be characterized into 2 groups, first group having higher PBC k values i.e. 
Talawakelle, Hantane, Deniyaya and the second group having lower PBC k values 
i.e. Ratnapura, Kottawa and Passara soils. 
Considering all parameters used for characterization, the following key could 
be prepared. 
6 0 
o 
"200 
M "400 
E 
^ - 6 0 0 
- 800 
"logo 
" 1 2 0 0 1 
+ 2 0 0 r 
•20 30 40 50 
104 x ARK 
(a) 
op 
4 -
' 2 0 0 
4 0 0 
6 0 0 
"800 
' 1 0 0 0 
1200 
UOO 
Fig. 2: Quantity/Intensity Isotherm ofDeniyaya Soil 
a. from 0-15 cm soil 
b. from 15-30 cm soil 
1 0 20 30 40 50 
104 x ARK 
(b) 
+200. 
"200 
-400 
'55 
| -«o 
^ -800 
"1000 
"1200 
1 0 20 30 40 50 
10" x ARK 
(a) 
-1400 1 
+200 
0 
-200 
-400 
'35 
1a> -600 
^ -800 
-1000 
-1200 
7 10 20 30 40 50 104 x ARK 
0>) 
Fig. 3: Quantity/Intensity Isotherm of Hantane Soil 
a. from 0-15 cm soil 
b. from 15-30 cm soil 
61 
Fig. 5: Quantity/Intensity Isotherm of Passara Soil 
a. from 0-15 cm soil 
b.from 15-30 cm soil 
62 
200 
~4ob 
"600 
"800 
1000 
1200 
uoo 
+ 2 0 0 
0 
" 200 
- 400 
- 6 0 0 
- 800 
" 1 0 0 0 
"1200 
~U00 
"1600" 
"1800" 
"2000 
"2200-
1b " 2 0 3 0 40 50 
10" x A R K 
(a) 
10 4 
I 
200 
- 400 
- 600 
- 800 
-1000 
"1200 
Fig. 6: Quantity/Intensity Isotherm of Ratnapura Soil 
a. from 0-15 cm soil 
b.from 15-30 cm soil 
10 20 30 40 '50 
1 0 4 x A R K 
(b) 
.30 40 50 
10" x A R K 
(a) 
GO 
I 
+ 2 0 0 
0 
" 2 0 0 
" 4 0 0 
" 6 0 0 
- 8 0 0 
" 1 0 0 0 
" 1 2 0 0 
10 2 0 3 0 4 0 50 
1 0 4 X A R K 
(b) 
Fig.7: Quantity/Intensity Isotherm of Talawakelle Soil 
a. from 0-15 cm soil 
b.from 15-30 cm soil 
63 
Key to characterization of tea soils 
High available K —• Talawakelle 
High 
Buffering 
Capacity 
HighK 
Specific sites 
Low available K Hantane 
Tea 
Soils 
LowK 
Specific sites 
Low 
Buffering 
Capacity 
HighK 
* Specific sites 
LowK 
Specific sites 
-> Deniyaya 
Ratnapura 
-> Passara 
Kottawa 
According to the key prepared a first group is categorized as those soils having 
higher K buffering capacity, K specific sites, Available K, and Al concentration 
(Table 1). As a result of higher buffering capacities and K specific sites, the K 
absorption and desorption should be relatively high in this group, eg. Talawakelle. 
The second group is those having higher K buffering capacities and K specific 
sites but having lower available K and Al concentration (Table 1). Though absorption 
and desorption are greater, the available K is relatively low compared with the 
first group, eg. Hantane. 
Third group is those having higher K buffering capacities but with low K 
specific sites, eg. Deniyaya. 
Fourth group is those having lower K buffering capacities but with higher 
K specific sites, eg. Ratnapura. 
Fifth group is those having lower K buffering capacities and K specific sites, 
eg. Passara, Kottawa. 
6 4 
CONCLUSIONS 
Soils in the tea growing regions could be divided into two main groups 
according to their Potential Buffering Capacities of K (PBC k). First group consisting 
of higher PBC K values and second group having lower PBCk values. Sub-divisions 
of soils were also suggested related to presence of K-specific-sites, available K 
and exchangeable Al as well. Q/I isotherms indicated the presence of some specific 
sites for K ions in Ratnapura, Hantane and Talawakelle as against the other 3 
soils. Finally, soils in the tea growing regions were characterized into 5 groups 
according to their K dynamics. It is worthy to consider these groupings also in 
arriving at K-recommendations for tea in Sri Lanka. 
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Research Institute of Sri Lanka, Talawakelle, Sri Lanka. 
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65 
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6 6