The role of targets, criterion, environmental, and hydrological factors is illustrated in Figure 2. In this figure criterion factors are factors influenced by drainage on the one hand and the agricultural performance on the other.
An example of a criterion factor is the depth of the
water table:
A drainage system influences this depth; the relation between drainage system design and depth of water table is mainly physical and can be described by
drainage equations, in which the
drainage requirements are to be found from a
water balance.[1]
The depth of the water table as a criterion factor needs to be translated into a criterion index to be given a numerical value that represents the behavior of the water table on the one hand and that can be related to the target (e.g. crop production) on the other hand.
The relation between criterion index and target can often be
optimized, the maximum value providing the ultimate aim while the corresponding value of the criterion index can be used as an agricultural drainage criterion in the design procedure.
Crop response processes
The underlying processes in the optimization (as in the insert of Figure 2) are manifold. The processes can be grouped into mutually dependent
soil physical, soil
chemical/biological, and
hydrological processes (Figure 3):
In drainage research the collection and analysis of field data is important.[5]
In dealing with field data one must expect considerable
random variation owing to the large number of natural processes involved and the large variability of plant and soil properties and hydrological conditions.
An example of a relation between crop yield and depth of water table subject to random natural variation is shown in the attached graph. The graph was made with the
SegReg program, see
segmented regression.
In irrigated lands, subsurface drainage may be required to
leach the salts brought into the soil with the irrigation water to prevent
soil salination.
Agro-hydro-salinity and
leaching models like
SaltMod[6] may be helpful to determine the drainage requirement.
References
^Drainage for Agriculture: Hydrology and Water Balances. Lecture notes, International Course on Land Drainage (ICLD), International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. Download at :
[1]
^Ahiablame, L.M.; Chaubey, I.; Smith, D.R.; Engel, B.A. (2011). "Effect of tile effluent on nutrient concentration and retention efficiency in agricultural drainage ditches". Agricultural Water Management. 98 (8): 1271–1279.
doi:
10.1016/j.agwat.2011.03.002.
ISSN0378-3774.
^Agricultural Drainage Criteria. Chapter 17 in: H.P.Ritzema (ed., 1994), Drainage Principles and Applications, Publication 16, p.635-690. International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands.
ISBN90-70754-33-9. Download at :
[2]
^Data provided by various authors on banana, cotton, sugarcane and wheat response to shallow water tables
[3]
^Drainage Research in Farmers' Fields: Analysis of Data. Part of project “Liquid Gold” of the International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands.
Download at :
[4]
^SaltMod: A tool for interweaving of irrigation and drainage for salinity control. In: W.B.Snellen (ed., 1997), Towards integration of irrigation, and drainage management. Special report, p. 41-43, International Institute for Land Reclamation and Improvement (ILRI), Wageningen, The Netherlands. Download at :
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