Scientific registration n° 1579
Symposium n° :14
Presentation : Poster
Study on relationship between quantity-intensity
characteristics of potassium in paddy soils and potassium
application
Etude des relations entre caractéristiques et doses de
potassium dans la fertilisation des sols de rizière
LI Huaxing (1), LI Guoful (2), MA Manzhuang (2), HUANG Xiaohong (2)ª ¤
(1)South China Agricultural University,510642,Guangzhou,Chinaª¤
(2)Guangdong Academy of Agricultural Sciences,Guangzhou,China
Summary
This paper discusses the Q/I characteristics of potassium in paddy soils.The results show that PBCk
is significantly correlated with clay content of soil. K¡ã has positive correlation with soil
exchangeable K and is significantly correlated with the relative percentage of rice yield.AReª¬k is
negatively correlated with clay content of soil and closely related to the frequancy of potassium
application.
Since the Q/I concept was put forward by Schofield(1947),Beckett (1) used the Q/I curves and its
relevant parameters to evaluate the status of soil potassium.AReª¬k could be used to measure the
potassium availability,-∆K could be used as an index for avaluating the amount of soil available
potassium,while potential buffering capacity of soil potassium could be estimated by PBCk.Some
researches shown that PBCk was significantly correlated with CEC(2,5),and -∆K° was significantly
correlated with soil exchangeable K(5). Lin(3) reported that PBCk was significantly correlated with
the total amount of potassium absorbed by paddy rice under pot culture without potassium fertilizer
for continual four crops.The aim of this study is to find out the retationship between Q/I
charateristics of potassium in paddy soils with different texture and potassium application.
Materials and methods
The paddy soils used were sampled from 13 counties in Guangdoug Provinces and their properties
are listed in Table 1.
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Table 1 Soil physical and chemical properties of the investigated soil samples
N°
Texture
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Clay loam
Clay loam
Clay loam
Clay loam
Clay loam
Clay loam
Clay loam
Clay loam
Clay loam
Loam
Sandy clay loam
Sandy clay loam
Sandy loam
Sandy loam
Organic matter
(g/kg)
43.2
42.0
35.0
39.0
36.0
29.6
47.6
40.6
35.1
49.0
41.0
37.0
37.0
24.0
26.7
< 0.002 mm clay
(%)
30.0
32.6
28.0
23.2
24.0
24.6
20.2
21.2
29.8
16.8
32.8
16.7
21.0
0.80
8.6
K*
(mg/kg)
58.1
72.6
61.4
71.4
59.8
56.4
55.2
81.8
68.9
82.6
55.6
91.3
51.5
34.9
56.0
*Exchangeable K: 1mol/L ammonium acetate extration and flame photometer method.
Field exeperiment
Experiment 1:The experiment with two treatments,one received potassium (potassium chloride,225
kg/hm²)and the other had no potassium application,was conducted in 15 soils.Each experiment was
carried out in four repetitions and each treatment received enough nitrogen and phosphate .Paddy
rice was the tested plant transplanted in eary season and late season seperately.
Experiment 2:The experiment with 5 treatments of split application of potassiun and three repeats
was conducted in sandy loam soil and clay loam soil .The treatments were as follows:
1.No potassium fertilizer.
2.100% potassiumm(225Kg/hm²) was applied as basal dressiug.
3.50% of the total potassium as basal dressing and 50% as topdressing on 18th days after
transplanting.
4.50% as basal and 50% at panical initiation.
5.50% as basal,30% on the 18th day after transplanting and 20% at panical initiation, respectively.
Analyses
Five grams of soil were equilibrated with 50ml mixed solutions containing 0.01 mol/L CaCl2 and
0,10,20,30,50,70,90,100 mg/L KCl separately.The suspensions were shaken on a rotary shaker at
25°C for 30 minutes.Potassium was determined in the filtrate,using flame photometer,while
calcium and magnesium were determined by atomic absorption spectrometer.∆K can be calculated
according to the difference between initial and final equilibrium potassium concentrations.The
2
ak
1/2. The Q/I curve was plotted by using ∆K as
a(Ca+ Mg )
ordinate and ARk as abscissa.- ∆K°, PBCk and ARk can be got from the Q/I curve(1,4).
potassium activity ratio ARk is equal to
Results and discussions
The Q/I curves in different soils
Figure 1 shows that the soils with different clay content present different Q/I curves.The curves
represent different potassium availability and potassium status.The parameters of Q/I curves of
different soils and its relative percentage of paddy rice yield are shown in Table 2.
Fig.1Q/I curves of the soils with different texture
Soil potassium potential buffering capacity(PBCk)
∆(∆K ) 

k
The PBCk is an index of soil potassium capacity  PBCk =
 . The figure 2 shows that PBC
∆ΑRk 

is significantly correlated with the clay contents of the siols(r=0.665**).Zhu's study (5) indicated
that PBCk and CEC are significantly correlated,and the same is true for CEC and the clay content of
soil.This means that the value of PBCª¬K can be measured by the amount of soil clay.Lin (3) has
proved that PBCk is significantly correlated with the amount of potassium absorbed by paddy rice
in continual four crops under pot cultrue without potassium fertilizer.But this study shows that
PBCk has no correlation with the amounnt of potassium absorbed by paddy rice and relative
percentage of rice yield in one crop (Table 2).The result indicates that the value of PBCk can only
reflect the long-term potential ability of soil potassium supply.
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Table 2 The main parameters of Q/I curves of the soil in relation to the relative percentage of rice
yield
N° Texture
-∆K°
(mg/kg)
Arkex10-4 PBCkx104
(mol/L)1/2 [(mg/kg)/(mol/L)1/2]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
50.9
72.9
62.3
64.4
58.2
55.8
40.5
88.5
67.0
85.6
43.4
85.8
48.0
25.2
56.0
9.50
19.55
15.27
13.56
12.28
12.25
9.73
19.73
19.82
16.48
8.54
57.60
39.87
25.98
54.38
Loam clay
Loam clay
Loam clay
Loam clay
Loam clay
Loam clay
Loam clay
Loam clay
Loam clay
Loam
Loam
Sandy clay loam
Sandy clay loam
Sandy clay loam
Sandy clay loam
5.36
3.73
4.08
4.75
7.74
4.56
4.16
4.47
3.38
5.19
5.08
1.49
1.21
0.97
1.03
Relative
percentage
of yield (%)
89.7
93.9
90.5
93.2
90.0
87.9
88.1
99.0
94.0
97.0
87.2
90.0
87.0
79.3
87.7
Increase rate
of rice yield
(%)
10.3
6.1
9.5
6.8
10.0
12.1
11.9
1.0
6.0
3.0
12.8
10.0
13.0
20.7
12.3
The results of this study show that the value of ∆K° is significantly correlated with the soil
exchangeable potassium (Y(-∆K°) = -16.04+1.196X(k),r=0.956**).The mean value of -∆K is not
different from that of soil exxhangeable potassium and the result is different from that in upland
soils(5).The result also indicates that both -∆K° and exchangeable potassium have positive
correlation with relative percentage of rice yield(r(-∆K°)=0.874**,r(k)=0.830**).Therefore both -∆K°
and the soil exchangeable potassium can reflect the soil potassium supply ability and can be used as
the main parameters for estimating the amount of soil potassium supplement during rice growing
season. -∆K° has significantly negative correlation with the increase rate of rice yield increased by
potassium fertilizer(Y(-∆K°)=92.3-3.3X(increase rate of rice),r=-0.874**).When the value of -∆K° is at the
level of 92.3 mg/kg,rice yield may not be increased by potassium fertilizer.
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Soil liable potassium(ARek)
Figure 3 shows that ARek has significant negative correlation with the amount of soil clay(Y(ARek) =
43.61-0.968X(clay),r=-0.541*),but has no significant correlation with relative percentage of rice
yield. ARek,as an intensity index of soil liable potassium,is of impotance in determining the
potassium fertilizer distribution during the rice growing period.Table 3 shows that rice yield is the
highest in sandy loam with an ARek value of 29.9x10-4(mol/L)1/2 when potassium was applied in a
three-split application,i.e.50%,30% and 20% of the total potassium fertilizer were applied befor
transplanting,18 days after transplanting and at panical initiation respectively.In clay loam with an
ARek value of 12.2x10-4(mol/L)1/2,the rice yield is increased by potassium fertilizer when
potassium was applied in one or in two-split application,namely,100% of the total potassium
fertilizer was applied before transplanting, or 50% before transplanting and the remainder on the 18
day after transplanting(or at panical initiation).It is obvious that the sandy soils with a high value
of has a strong supply intensity of potassium and the frequency of potassium application could be
increased to meet the demand of the rice plant,but the clay loam is on the contrary,thus the
frequency of potassium application could be reduced.
Table 3 The effect of split application of potassium on the rice yield in the soils with different ARek
values
Treatment n°
1
2
3
4
5
ARek = 29.9x 10-4
(Saddy loam, Guangzhou)
Yield
Relative percentage
5443.5
100
5731.5
105.3
5794.5
106.4
5832.0
107.1
6031.5
110.8
Conclusion
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ARek = 12.2x 10-4
(Clay loam, Guangzhou)
Yield
Relative percentage
4600.5
100
5266.5
114.5
5449.5
118.5
5184.0
112.7
4983.0
108.7
The paddy soils with different clay content show different Q/I curves which indicate soil potassium
status.
PBCk, parameter of soil potassium capacity,has positive response to soil clay(r=0.665**),and can
reflect the long term potential ability of soil potassium supply. The value of -∆K° has positive
correlation with soil exchangeable potassium and is significantly correlated with the relative
percertage of rice yield(r=0.874**),and has significantly negative correlation with the increase rate
of rice yield increased by potassium fertilizer(r=-0.834**).When -∆K° value is at 92.3mg/kg,paddy
rice may has no response to potassium fertilizer. ARek has a significant negative correlation with
the soil caly (r=-0.541*).The value of ARek may be used as a parameter for determining the
frequency of potassium application.
References
1. Beckett,P.H.T.,1964: Studies on soil potassiumI and II. J.Soil Sci.15,1
2. Huang, Changyong and Xie Zhengmiao and Jiang Qiuyi,1987: The correlation of soil buffering
power and potential buffering capacity with soil K critical level.Acta Agriculturae University
Zhejiangensis.13(1):84-90
3. Lin, Zhongyan,1987: Application of thermodynamic Parameters in dianosing potassium
requirement of paddy soils.Acta Pedologica Sinica,24(1):35-41
4. Sparks,D.L.and Huang P.M.,1985: Physical Chemistry of soil potassium.Potassium in
Agriculture,R.D.Munson(ed.)201¡«276.ASA.CSS and SSSA,Madison,WI
5. Zhu, Yongguan and Luo Jiaxian,1993: Q/I characteristics of potassium in soils in South
China.Tropical and Subtropical Soil Science,2(2),73-80
Key words:Q/I curve,Potassium potential buffering capacity,exchangeable K,clay
content,relative percentage of rice yield
Mots clés : courbe Q/I, pouvoir tampon potentiel, K échangeable taux d'argile, pourcentage relatif
du rendement en riz
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