Global food security and stability deeply depends on the management of
the natural resources. Today, some 40% of all world food is obtained from
irrigated farmlands. Food production via irrigated agriculture, however,
does not correspond to the current rapid population growth. Soil salinity
and contamination in addition to the excessive urban development are also
the main factors that affect the state of food production by irrigated
agriculture (Conway, 2003).
The available water resources may not be able to meet various demands
that will inevitably result in the irrigation of additional lands in order
to achieve a sustainable global food security. The suitability, by definition,
is the natural capability of a given land to support a defined use. The
process of land suitability classification is the appraisal and grouping
of specific areas of land in terms of their suitability of a defined use.
According to the FAO (1976), methodology this is strongly related to the
land qualities including erosion resistance, water availability and flood
hazard that are not measurable. As these qualities derive from the land
characteristics, such as slope angle and length, rainfall and soil texture
which are measurable or estimable, it is advantageous to use these latter
indicators in the land suitability studies. Thus, the land parameters
are used to obtain land suitability for irrigation purposes. Sys et
al. (1991) suggested a parametric evaluation system for irrigation
methods which was primarily based upon physical and chemical soil properties.
In the proposed system the factors affecting the soil suitability for
irrigation purposes can be subdivided into four groups:
||Physical properties determining the soil-water relationship in the
soil such as permeability and available water content
||Chemical properties interfering with the salinity/alkalinity status
such as soluble salts and exchangeable Na
||Environmental factors such as slope
Hired et al. (1996) and Bond (2002) improved the classification
methods for evaluating suitability for effluent irrigation and land suitability
for irrigation. These factors influence the land suitability in an irrigation
practice included soil properties and topography. Tesfai (2002) investigated
a land suitability method for gravity (surface) irrigation schemes in
the Sheeb area of Eritrea. According to the results, in surface irrigation
practice, 16% of the study area was highly to moderately suitable (S1
and S2), 24% was classified as moderately suitable (S2),
17% was marginally suitable (S3) and 40% of the area was decided
as unsuitable (N1) for surface irrigation. The main limiting
factor for surface irrigation was soil salinity, Bienvenue et al.
(2003) evaluated the land suitability for surface (gravity) and drip (localized)
irrigation in the Thies, Senegal using the parametric evaluation system
proposed by Sys. Under surface Irrigation, there was no area classified
as highly suitable (S1). Only 20.24% of the study area proved
suitable (S2, 7.73%) or slightly suitable (S3, 12.
51%). Most of the study area (57.66%) was classified as unsuitable (N2).
The limiting factor to this kind of land use was mainly the soil drainage
status and texture that was mostly sandy while surface irrigation generally
requires heavier soils. For drip and localized irrigation, a good portion
(45.25%) of the area was suitable (S2) while 25.03% was classified
as highly suitable (S1) and only a small portion was almost
suitable (N1, 5. 83%) or unsuitable (N2, 5.83%).
In the latter cases, the handicap is given by the shallow soil depth,
bad texture due to a large amount of coarse gravel and/or poor drainage.
Mbodj et al. (2004) performed a land suitability evaluation for
two types of irrigation i.e., surface irrigation and drip irrigation in
Tunisian Oued Rmel Catchment using the suggested parametric evaluation.
According to the results, the drip irrigation suitability gave more irrigable
areas compared to the surface irrigation practice due to the topographic
(slope), soil (depth and texture) and drainage limitations worked out
in the surface irrigation suitability evaluation. Rees and Laffan (2004)
studied the land suitability for spray irrigation in the Southwood Processing
Complex, southern Tasmania. In this research, soil properties such as
depth, texture, structure, hydraulic conductivity, massive hardpan, stone
content and topographic properties such as slop, land form, surface rock,
frequent waterlogging and drainage properties were considered as to be
the main factors in land suitability evaluation for any spray irrigation
Barberis and Minelli (2005) provided land suitability classification
for both surface and drip irrigation methods in Shouyang country, Shanxi
province, China. The study was carried out by a modified parametric system.
The results indicated that due to the unusual morphology, the area suitability
for the surface irrigation (34%) is smaller than the surface used for
the drip one (62%). The most limiting factors were physical parameters
including slope and soil depth.
Intensive application of water alters water distribution in the surroundings
and affects the transfer rate of the pollutants in the soil, soil density,
erosion, salinity, alkalinity, waterlogging, etc. Water and soil compatibility
in any irrigation practice is of outmost importance and should it be no
so, irrigation water will bring about adverse impacts on the physico-chemical
properties of the soil in long run. To determine the main objective of
this study is to evaluate and compare land suitability for surface and
drip irrigation methods according to the parametric evaluation for Shavoor
Plain. To determine such compatibility, detailed evaluation of soil properties
and topography is required.
MATERIALS AND METHODS
The present study was conducted in an area about 77706 hectares in Shavoor
Plain in Khuzestan province, southwest of Iran in year of 2006. The study
area is located 40 km north Ahwaz between 31° 37´, 32°
30` N and 48°15´, 48°40` E. Average annual temperature
and precipitation for the period of 1966-2004 were 25.3°C and 260
mm, respectively. The annual evaporation is over 2000 mm (KWPA, 2005).
The main water resource to this area is Shavoor river. The study area
has been commonly used for irrigated agriculture. Presently, the irrigation
systems used by farmlands are furrow irrigation, basin irrigation and
border irrigation schemes.
The area is composed of three distinct physiographic features i.e., plateau
river, alluvial plain and low land, particularly river alluvial plain physiographic
units are common. Twenty five different soil series were found in the area.
To determine soil a characteristic, the semi-detailed soil survey report of
Shavoor was used (KWPA, 2006). The land evaluation was determined based upon
topography and soil characteristics. The topography characteristics included
slope while soil properties included soil texture, depth, salinity, drainage
and carbonate content. Also, soil properties such as Cation Exchange Capacity
(CEC), Percentage of Basic Saturation (PBS), organic mater (%OM) and pH were
considered in terms of soil fertility. Sys et al. (1991) suggested that
soil characteristics such as %OM and PBS do not require any evaluation in the
arid regions while clay CEC rate usually exceeds the plant requirement without
further limitation, thus, fertility properties can be excluded from land evaluation
with the purpose of irrigation.
Based upon the profile description and laboratory analysis, that group
of soils that had similar properties and located in a same physiographic
unit were considered as a series of soils and were taxonomies to form
a soil family as per to keys to soil taxonomy 2006. Ultimately, 25 soil
series were selected for the surface and drip irrigation land suitability.
For determination the average of soil texture, salinity and CaCO3
for the upper 150 cm of soil surface, the profile was subdivided into
6 equal sections and weighting factors 2, 1.5, 1, 0.75, 0.5 and 0.25 were
used for each section, respectively (Sys et al., 1991).
For the evaluation of land suitability to surface and drip irrigation,
the parametric evaluation system was used (Sys et al., 1991). This
method is based on morphology, physical and chemical properties of soil.
||Suitability classes for the irrigation capability indices (Ci) classes
Six parameters were considered which are, slope, drainage properties,
electrical conductivity of soil solution, calcium carbonates status, soil
texture and Soil depth.
Rates are assigned to the aforementioned six parameters as per the related
tables, thus, a capability index for irrigation (Ci) was developed as
shown in the equation below:
In which, A, B, C, D, E and F are soil texture rating, soil depth rating,
calcium carbonate content rating, electrical conductivity rating, drainage
rating, slope rating, respectively.
In Table 1, the ranges of capability
index and the corresponding suitability classes are shown.
Twenty-five soil series and sixty-five series phases were derived from
the semi-detailed soil study of the area. The soil series are shown in
Fig. 1 as the basis for any land evaluation practice. The soils of the
area are of Aridisols and Entisols orders. Also, the soil moisture regimes
are Aquic and Ustic while the soil temperature regime is Hyperthermic
As shown in the Table 2, 3 and Fig.
2, 3 for the surface or gravity irrigation, the
soil series coded 1, 4, 5, 13, 14, 15, 16, 18, 20 and 21 (31702. 46 ha-40.82%)
were classified as moderately suitable (S2) and soil series
coded 2, 8, 9, 18, 19 and 24 (14549. 48 ha-18.72%) were found to be marginally
For drip and localized irrigation, soil series coded 2, 4, 5, 14 and
15 (14952.07 ha-19.24%) are highly suitable (S1) and soil series
coded 1, 8, 13, 16, 17, 18, 20, 21 and 25 (22813.78 ha, or 29.36%) were
classified as moderately suitable (S2). Only soil series coded
9, 19 and 24 (8484.09 ha-10. 92%) were found to be slightly suitable (S3).
Moreover, soil series coded 3, 6, 7, 10, 11, 12, 22 and 23 (27578. 26
ha-35.49%) were classified either currently or permanently as not-suitable
(N1 and N2) for both surface and drip irrigation
The results of Table 4 indicate that by applying drip irrigation instead
of surface irrigation methods, suitability classes of soil series coded
4, 5, 14 and 15 (11931.44 ha, or 15.35%) improved from moderately suitable
(S2) to highly suitable (S1) and soil series coded
2 (3020.63 ha or 3.89%) improved from marginally suitable (S3)
to highly suitable (S1). In addition, soil series coded 8 and
17 (3042.76 ha-3.92%) developed from marginally suitable (S3)
to moderately suitable (S2) and soil series coded 7 (3503.36
ha-4.51%) developed from permanently not suitable (N2) to currently
not suitable (N1).
||Soil map of the study area
||Ci values and suitability classes of gravity and drip irrigation
for each soil series
||Land suitability map for surface irrigation
||Comparison of the land units for both surface and drip irrigation
The comparison of the two types of irrigation revealed that the drip irrigation
was more effective and efficient as the latter mode improves the suitability
to the irrigation purposes. Moreover, The main limiting factors in using
both surface and drip irrigation
methods in this area were soil salinity
and drainage. Briza et al
. (2001) applied a parametric system (Sys
., 1991) to evaluate land suitability for both surface and drip
irrigation in the Ben Slimane Province, Morocco while no highly suitable
areas were found in the studied area. The largest part of the agricultural
areas was classified as marginally suitable the most limiting factors being
physical parameters such as slope, soil texture
and soil depth. Dengiz (2005)
also compared different irrigation methods including surface and drip irrigation
in the pilot fields of central research institute, lkizce research farm
located in southern Ankara. He concluded that with the drip method increased
the land suitability by 38% compare to the surface irrigation method.
The most important limiting factors for surface or gravity irrigation
in study area were soil salinity, drainage and soil texture, respectively
whereas, the major limiting factors for drip or localized irrigation were
soil salinity and drainage.
Details are given of the analyzing field data to compare the suitability
of two irrigation systems. The analyzing parameters included soil and
land characteristics. The results showed that drip irrigation proved more
suitable than surface irrigation system in the study area, however, the
major limiting factors for the both irrigation methods were soil salinity
and drainage. Since drip irrigation system typically applies small amount
of water on a frequent basis, maintaining soil water near field capacity,
therefore, it would be more benefit to use the drip irrigation method.
In arid climates and regions, hence, is recommended to be exercised as
the best suitable method for the study area.
Thanks to the Research and Standards Office for Irrigation and Drainage
Networks of KWPA for Financial supports and all assistance.