Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RICE 157
some organic soils such as peaty soils.
3.11.2. Iron in soil solution
The concentration of ferrous iron in the soil solution increases sharply after
submergence (Fig. 3.23). After 4 weeks of submergence strongly acid latosolic
soils build up in the soil solution concentrations as high as 300 ppm Fe 2+ and then
show an exponential decrease. After about 6 months of submergence, concentrations
are maintained at about 50–100 ppm. The slightly acid soils give maximum
concentrations of 50–100 ppm, while slightly alkaline soils low in organic matter
may not attain peak concentrations of more than 30 ppm. Such concentrations are
still much higher than the concentrations of 2–5 ppm normally used for the culture
solution. In general, the concentration of iron in the soil solution is controlled by
soil pH, organic matter content, iron content itself, and the duration of submergence.
3.11.3. Iron deficiency
a. High pH-induced iron deficiency. Iron chlorosis commonly occurs on high-pH
soils and culture solutions. Iron-deficient plants induced by high pH normally
contain high percentages of iron in the roots and low percentages in the shoots.
3.23. Changes in the concentrations
of Fe 2+ in the soil solution
of 5 soils (Ponnamperuma
1965).