Yoshida - 1981 - Fundamentals of Rice Crop Science

182 FUNDAMENTALS OF RICE CROP SCIENCE
ribonuclease is useful for diagnosing zinc deficiency in orchard trees (Kessler
1961).
a. Units and expressions used for analytical results. In inorganic analysis, two
units are commonly used on a dry weight basis:
Thus,
Percentage (%): grams nutrient per 100 gram plant material
Parts per million (ppm): milligrams nutrient per kilogram plant material
1% = 10 4 ppm
The expression of chemical form for analytical results varies among reports. In
the old literature, analytical results are normally given in the form of oxides such as
P 2 O 5 and K 2 O. In recent years, the trend is to use the elemental forms such as P and
K. Under most conditions, convenience dictates which form to use. In greenhouse
and laboratory studies, the elemental forms are preferred because they are simpler.
Some scientists use milligram atom or microgram atom percent. These expressions
may be useful in basic studies where, for example, the element content is
related to an enzyme activity. However, they should be avoided in plant tissue
analysis for diagnostic purposes and related greenhouse studies.
b. Sampling procedure. In sampling plant materials, problems are often
encountered in determining which plant parts to sample, when to sample, and how
to replicate the sampling.
The whole shoot, the leaf blades, or the Y -leaf (the most recently matured leaf
blade) are normally used for tissue analysis in rice (Yoshida et al 1976). In most
cases, deficiency or toxicity symptoms appear when plants are young and small;
hence, the whole plants (excluding roots) may be sampled for chemical analysis.
The grain is generally not suitable for diagnosis because its chemical composition
is least affected by the nutrient supply.
The rice leaf sheath functions as a storage organ for potassium, and the
potassium content of the leaf blade tends to be maintained at the expense of the leaf
sheath. When the plant becomes deficient in potassium, a larger decrease occurs in
Table 4.2. Potassium content in different parts of the rice plant
at panicle initiation. a
K content (%) in
Plant Position Normal K-deficient
part plants plants
Leaf blade Upper 2.90 1.51
Lower 2.88 1.21
Leaf sheath Upper 3.36 0.90
Lower 3.68 0.52
a
Matsuzaka et al (1962).