Yoshida - 1981 - Fundamentals of Rice Crop Science

152 FUNDAMENTALS OF RICE CROP SCIENCE
Table 3.26. Effects of a moderately high concentration of sodium chloride on the
growth and potassium requirement of the rice plant at the vegetative growth stage. a
Nutrient content of shoot (%)
Potassium Dry shoot wt
supply (g) K Na
(ppm)
No 1000 ppm No 1000 ppm No 1000 ppm
NaCl NaCl NaCl NaCl NaC l NaCl
1 9.0 15.7 0.33 0.30 0.14 1.63
2 16.0 21.8 0.56 0.56 0.15 1.76
5 24.2 30.4 0.76 0.77 0.12 1.39
10
31.7 38.5 1.23 0.92 0.10 1.24
50
33.4 36.3 1.18 1.11 0.12 1.37
100
39.9 36.7 1.51 1.34 0.09 1.03
200 47.7 44.2 2.75 1.80 0.10 0.98
a Yoshida and Castañeda (1969).
3.10. ZINC
3.10.1. Occurrence of deficiency
Zinc deficiency of lowland rice occurs widely in near-neutral to alkaline soils,
particularly calcareous soils. In a severe case of zinc deficiency, transplanted rice
seedlings may die or direct-sown seeds may fail to emerge. In most cases,
however, symptoms become visible about 2–3 weeks after transplanting and a
spontaneous recovery from the deficiency may occur 6–8 weeks after soil submergence.
3.10.2. Zinc in soil solution
The availability of both soil zinc and applied zinc is much higher in upland soils
than in submerged soils (Yoshida 1975c). Soil submergence causes a substantial
decrease in the zinc concentration in the soil solution (Fig. 3.18). After prolonged
submergence, the zinc concentration tends toward an ultimate value between 0.02
and 0.03 ppm. In a solution culture experiment using 2 varieties, the critical low
concentration for zinc deficiency was about 0.01 ppm (Fig. 3.19). Zinc concentrations
in the culture solution for other plant species to attain maximum growth range
from 0.003 to 0.016 ppm (Carroll and Loneragan 1968).
In Maahas and Luisiana soils, soil pH increases substantially during the first 3
weeks after submergence, during which zinc concentrations fall rapidly. Since the
solubility of zinc decreases with increasing pH, decreases in zinc concentration
might be predicted; however, factors other than soil pH could be operating. For
example, in Kala Shah Kaku soil, where zinc deficiency occurs, a substantial
decrease in zinc concentration during the first 2 weeks is not accompanied by any
increase in soil pH. The ultimate value of the zinc concentration in the soil
solution, however, is considered adequate for healthy plant growth. Thus, zinc