Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RICE 137
3.11. Selective absorption of ammonia and nitrate from ammonium
nitrate in culture solution (Tadano and Tanaka 1976).
deficiency at higher pH values, sometimes makes it difficult to draw a conclusion
with confidence.
At early growth stages and with up to 200 ppm N, rice grows better with
ammonia than with nitrate, whereas cucumbers grow better with nitrate (Oji and
Izawa 1974). Upland crops such as Azuki bean, radish, sugar beet, and soybean
use nitrate better than they do ammonia even at 14 ppm N (Tadano and Tanaka
1976). After panicle initiation and at 100 ppm N, which is unusually high for this
growth stage, nitrate is a better nitrogen source for rice than ammonia. At 20 ppm
N, however, ammonia is as good as nitrate (Tanaka et al 1959). Therefore, at
realistic levels of nitrogen concentration in the soil solution, ammonia appears to
be better than or as good as nitrate throughout the rice plant’s entire growth cycle.
Rice absorbs ammonia in preference to nitrate from a solution that contains
both. Excised roots from rice seedlings absorb ammonia 5 to 20 times faster than
nitrate, depending on the solution pH (Fried et al 1965). With intact plants, rice
also absorbs ammonia faster than nitrate, whereas the opposite is true with sugar
beets (Fig. 3.11). Although rice prefers ammonia, it does not accumulate free
ammonia in leaf tissues (Table 3.16); surplus ammonia is converted into
asparagine. Cucumbers, however, accumulate in plant tissue considerable quantities
of free ammonia, along with alanine and serine (Oji and Izawa 1974).