Agriculture Reference
In-Depth Information
Fig. 3. Map of Taiwan and location of communities where the paddy fields are located
(Römkens et al., 2009).
Soil pH, CEC (Cation Exchange Capacity), and soil organic matter (SOM) varied widely in
the 19 paddy fields (Table 7). Cadmium concentrations in rice grains were quite different
among cultivars even though they were planted in soils with comparable soil properties and
total soil Cd levels. Overall, median Cd concentrations in rice grains of Indica variety were
2-3 times higher than that of Japonica variety no matter the rice is planted in low or high Cd-
contaminated fields or in different climates (Fig. 4). Higher variation was found in the
concentration of Cd in Indica brown rice compared with that in Japonica brown rice. Some
studies also found that Cd accumulation in brown rice of Indica was 1.54 times higher than
that of Japonica. This uptake characteristic of rice varieties is important for selecting rice
cultivars with low Cd accumulating ability in rice grain planted in slightly Cd-contaminated
soil.
pH
CEC (cmol
+
kg
-1
)
SOM (%)
Total Cd (mg kg
-1
)
Japonica
3.8-7.2
2.6-24.2
1.4-9.5
0.06-27.8
Indica
4.1-7.0
2.6-25.1
1.3-10.2
0.08-25.9
Table 7. The pH, CEC, and SOM of the soils growing for two rice varieties.
Liu et al. (2007) reported that Cd was not evenly distributed in different parts of rice grain.
The results of their pot experiments planting six rice cultivars (include Indica, Japonica,
hybrid Indica, and New Plant type) in artificially Cd-contaminated soil showed that the
average percentage of Cd quantity accumulated in chaff, cortex (embryo), and polished rice
were about 15%, 40%, and 45%, respectively. The cortex occupied only 9% of the grain dry
weight in average but the polished rice occupied 71%, so Cd concentration in cortex is
significantly higher than that in polished rice. They suggested that polished rice produced
