Yoshida - 1981 - Fundamentals of Rice Crop Science

150 FUNDAMENTALS OF RICE CROP SCIENCE
3.17. Responses of two varieties to different levels of applied phosphorus (drawn from
Koyama et al 1973).
3.9.2. Potassium in soil solution
Submergence increases the concentration of potassium in the soil solution. The
increases are higher in sandy soils rich in organic matter and are associated with
soluble ferrous iron and manganese (Table 3.24). This can be considered one of
the benefits of flooding. A disadvantage, however, would be the loss in coarsetextured
soils with drainage.
3.9.3. Partial productive efficiency
The partial productive efficiency of potassium for grain is generally high at early
growth stages, declines, and becomes high again at later stages (Table 3.25). Since
rice requires large quantities of potassium, a sustained supply is necessary up to
heading when the reproductive stage is complete. Note that only 20% of the
absorbed potassium is translocated to the panicles; the rest remains in the vegetative
parts at maturity (see Table 3.11).
3.9.4. Partial replacement of potassium by sodium
Since most of the enzymes requiring univalent cations are not activated by sodium