Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RICE 151
Table 3.24. Relationship between increase in concentration of K + in the soil solution
on submergence and soil properties. a
Soluble
Soil Organic Ex K + Soluble K + (ppm) Fe ++ and
no. pH matter Texture (ppm of Mn ++
(%) soil) Start Peak Increase (ppm)
25 4.8 4.4 Fine sandy loam 140 7.6 12.5 5.9 230
18 5.6 6.0 Sandy loam 185 6.3 12.7 5.4 90
1 7.4 2.6 Loamy fine sand 100 3.2 5.2 2.0 73
28 4.7 2.9 Clay 165 2.3 7.9 5.6 342
14 4.7 2.3 Clay 108 2.4 6.5 4.1 340
31 6.2 3.4 Clay 160 3.5 6.0 2.5 174
4 6.9 1.8 Clay 60 1.6 1.9 0.3 39
a Ponnamperuma (1965).
(Evans and Sorger 1966), sodium can only substitute for potassium to a limited
extent.
Replacement of potassium by sodium is probably possible in less specific
processes, such as the maintenance of cell turgor and when potassium is limited.
One of the potassium deficiency symptoms in rice is droopy leaves. When sodium
chloride is added, however, the leaves remain erect, suggesting that droopy leaves
are caused by reduced cell turgidity. Sodium absorption helps maintain the high
turgidity responsible for erect leaves (Yoshida and Castañeda 1969).
When potassium is limited, the addition of 1,000 ppm of sodium chloride to the
culture solution improves vegetative growth, which eventually results in increased
panicle yield (Table 3.26).
The antagonistic effect of sodium on potassium absorption by rice varies with
the level of potassium supply. Sodium chloride decreases the potassium content
only when the supply of potassium is high, but it has no effect on potassium when
the supply is low. This suggests that a relatively high sodium content can benefit
rice nutrition under weakly saline conditions and when the potassium supply is
limited.
Table 3.25. Partial productive efficiency of potassium for
grains. a
Growth period b
Partial productive efficiency
Low K Medium K High K
12 Jul–22 JuI 0.051 0.082 0.046
22 Jul–1 Aug 0.058 0.082 0.058
1 Aug–11 Aug 0.049 0.065 0.019
11 Aug–21 Aug 0.007 0.014 0.004
21 Aug–31 Aug 0.021 0.007 0.023
a Kiuchi (1952). b Transplanting = 12 Jul; heading = 5 Sep.