Agriculture Reference
In-Depth Information
0.15
r
h
cr
=
(9.25)
height of upflow, is inversely proportional to the radius of the capillary tube. Thus
for soil of clay type, i.e., soils having smaller diameter of pore, capillary rise will
be higher. For the sandy soil, due to larger diameter of pore, the reverse will be
true. Therefore, to minimize rise of groundwater within the root zone (or target soil
depth), drain should be placed at greater depth in clayey or fine-textured soil than
the coarse-textured soil (for similar crop and hydro-geologic condition).
9.6.2 Data Requirement for Subsurface Drainage Design
Data required for proper design of a subsurface drainage system include
•
soil layering
•
depth to layers restricting vertical flow
•
soil hydraulic properties (for each layer)
•
depth to water table
•
salinity status of soil and ground water
•
sources of drainage water other than deep percolation
•
cropping pattern and crop root zone depth
•
type of irrigation system
•
irrigation schedule
•
irrigation efficiency
•
climate data
Soils data collection and analysis is common to all design procedures. Sampling
and investigation of the soil must be done up to below the depth of potential drain
placement (2-4 m) to determine the presence of a restricting layer. The soil salinity
profile above the drain is useful to determine the need for remediation. The soil
salinity profile below the drains is needed because this will be indicative of the
potential salt load when the drains are in operation.
If the soil properties vary considerably within a farm, the area should be divided
into “sub-areas” or “blocks.” Then, drain spacing should be calculated for each sub-
areas or blocks.
9.6.3 Layout of Subsurface Drainage
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