Agriculture Reference
In-Depth Information
3.4.8.3 Stream Size/Flow Rate
In general, the larger the stream size available, the larger the furrow must be to
contain the flow. When larger stream sizes are available, water will move rapidly
down the furrows and so generally furrows can be longer. Normally stream sizes up
to 0.5 l/s will provide an adequate irrigation provided the furrows are not too long.
The maximum stream size that will not cause erosion will obviously depend on the
furrow slope. In any case, it is advisable not to use stream sizes larger than 3.0 l/s.
slope as
0.60
S
q
m
=
(3.21)
where
q
m
=
maximum non-erosive flow rate in individual furrow (l/s)
S
=
slope of furrow (%)
For normal conditions, flow rate can be estimated from
0.50
S
q
m
=
(3.22)
The units are the same as that of the earlier.
3.4.8.4 Furrow Shape
In sandy soil, water moves faster vertically than sideways (or lateral). Narrow,
parabolic, or deep V-shaped furrows are desirable to reduce the soil area through
which water percolates. However, sandy soils are less stable and tend to collapse,
which may reduce the irrigation efficiency.
In clay soils, the infiltration rate is much less than for sandy soils, and there is
much more lateral movement of water. Thus, a wide, shallow furrow is desirable to
obtain a large wetted area to encourage infiltration.
3.4.8.5 Spacing of Furrow
The spacing of furrows is influenced by the soil type and the cultivation practice.
Based on the crop and soil, it normally ranges from 50 to 80 cm.
3.4.9 Estimation of Average Depth of Flow from Volume Balance
Average depth of applied (or infiltrated) water can be estimated from volume
balance approach as follows:
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