Takaya et al. - 1974 - Rice cultivation and its environmental conditions
Takaya et al. - 1974 - Rice cultivation and its environmental conditions
Takaya et al. - 1974 - Rice cultivation and its environmental conditions
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222 Y. TAKAYA, K. KYUMA, <strong>and</strong> K. KAWAGUCHI<br />
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<strong>and</strong> at some places even receives so much water that the floor of the rice field must<br />
be raised up sever<strong>al</strong> ten-centim<strong>et</strong>ers so as to g<strong>et</strong> enough drainability. The dammed-up<br />
portion of the main v<strong>al</strong>ley is within the tid<strong>al</strong> zone. The water is mostly pumped up<br />
from tid<strong>al</strong> creeks with careful checking of the s<strong>al</strong>inity.<br />
·6) Sado V<strong>al</strong>ley (cf, Fig. 8)<br />
The Sado river is even sm<strong>al</strong>ler than the Mondego. The v<strong>al</strong>ley reve<strong>al</strong>s in most<br />
-places a loamy constituent throughout the whole of <strong>its</strong> cross-section rather than a<br />
-complicated web of levee <strong>and</strong> backswamp. Water is adequately supplied from upstream<br />
reservoir by can<strong>al</strong>s <strong>and</strong> is drained through natur<strong>al</strong> channels. This is a well irrigated<br />
·<strong>and</strong> well drained rice l<strong>and</strong>.<br />
The lowermost reach, however, below Alcacer do S<strong>al</strong>, has different features. Here,<br />
the whole breadth of the v<strong>al</strong>ley is actu<strong>al</strong>ly within the tid<strong>al</strong> range <strong>and</strong> has a clayey<br />
foundation. <strong>Rice</strong> growing must be done under the protection of tidewater control<br />
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