Yoshida - 1981 - Fundamentals of Rice Crop Science

MINERAL NUTRITION OF RlCE 123
Table 3.7. Growth and composition of the rice plant grown in soil and in soil leachate. a
Dry wt (g/pot) Nutrient content in leaves (%)
Panicles Leaves Roots N P 2 O 5 K 2 O CaO SiO 2
Soil-grown 105 75 13 0.74 0.19 4.5 0.90 5.7
Solution-grown 20 23 7 0.61 0.05 3.4 0.62 4.0
a Data were taken from No. 5 plots in Table 5 (Tanaka 1961b).
in response to the plant's absorption. In general, the labile pool represents the
major component of the quantity factor while the nutrient concentration of the soil
solution is the intensity factor. Nutrient absorption by plant roots is directly
dependent on the concentration of the soil solution (intensity factor), which in turn
is regulated by the labile pool (quantity factor). Introduction of the quantityintensity
concept into the dynamics of nutrient availability has proved useful in
understanding the relationship between nutrient uptake and soil nutrients. Further
details on the dynamics of nutrient availability are discussed elsewhere (Bache
1977, Mengel and Kirkby 1978).
3.4. NUTRIENT ABSORPTION
3.4.1. Active ion absorption
In their pioneering work on ion absorption by the fresh water algae Nitella clavata
and the roots of young barley seedlings, Hoagland and his associates demonstrated
that plant cells can absorb ions from a low-concentration solution (external) into a
high-concentration solution (cell sap) (Hoagland 1944, Epstein 1972). Such uphill
ion transfer does not occur spontaneously; the cells must expend energy to make
the ions move against the concentration gradient. The necessary energy must be
supplied by respiration within the tissues. The term active absorption or active
transport is used to refer to such energy-requiring ion movement.
If active ion absorption requires energy supplied by respiration, any factors that
affect the supply of the substrate necessary for respiration and the rate of respiration
would affect the rate of ion absorption. Evidence is cited below in support of
active ion absorption (Epstein 1972).
a. Accumulation ratio. The concentration of an ion may become far greater in
the cells than in the external solution. This is often called accumulation. The ratio
of the ion concentration within the cells to that of the external solution —
accumulation ratio — is about 1,000 or higher for potassium and chloride. A ratio
as high as 10,000 is not uncommon. The accumulation ratio tends to increase as the
external concentration decreases.
b. Temperature. The temperature coefficient (Q 10 ) for ion absorption is about 2
or higher, indicating that ion absorption is dependent on metabolic activity.
c. Oxygen. The absorption of many ions is affected by oxygen tension in the