Water Management in Horticultural Crops

Factors affecting the suitability of an irrigation method

The suitability of the various irrigation methods, i.e., surface, sprinkler or drip irrigation depends mainly on the following factors:

a. Natural conditions
b. Type of crop
c. Type of technology
d. Previous experience with irrigation
e. Required labour inputs
f. Costs and benefits

a. Natural Conditions

• The natural conditions such as soil type, slope, climate, water quality and availability have the following impact on the choice of an irrigation method:
Soil type

• Sandy soils have a low water storage capacity and a high infiltration rate. They therefore need frequent but small irrigation applications, in particular when the sandy soil is also shallow. Under these circumstances, sprinkler or drip irrigation are more suitable than surface irrigation. On loam or clay soils all three irrigation methods can be used, but surface irrigation is more commonly found. Clay soils with low infiltration rates are ideally suited to surface irrigation.
• When a variety of different soil types is found within one irrigation scheme, sprinkler or drip irrigation are recommended as they will ensure a more even water distribution.
Slope

• Sprinkler or drip irrigation are preferred above surface irrigation on steeper or unevenly sloping lands as they require little or no land leveling.
Climate

• Strong wind can disturb the spraying of water from sprinklers. Under very windy conditions, drip or surface irrigation is suitable. Sprinkler or drip irrigation may be more suitable than surface irrigation because of their flexibility and adaptability to varying irrigation demands on the farm.
Water availability

• Water application efficiency is generally higher with sprinkler and drip irrigation than surface irrigation and so these methods are preferred when water is in short supply. However, it must be remembered that efficiency is just as much a function of the irrigator as the method used.
• If the irrigation water contains dissolved salts, drip irrigation is particularly suitable, as less water is applied to the soil than with surface methods.
• Sprinkler systems are more efficient than surface irrigation methods in leaching out salts.
b. Type of crops

• Surface irrigation can be used for all types of crops. Sprinkler and drip irrigation, because of their high capital investment per hectare, are mostly used for high value crops, such as vegetables and fruit trees. They are seldom used for the low value staple crops.
• Drip irrigation is suited to irrigating individual plants or trees or row crops such as vegetables. It is not suitable for close growing crops.
c. Type of technology

• The type of technology affects the choice of irrigation method. In general, drip and sprinkler irrigation are technically more complicated methods. The purchase of equipment requires high capital investment per hectare. To maintain the equipment a high level of ‘know-how’ has to be available. Also, a regular supply of fuel and spare parts must be maintained.
• Surface irrigation systems, in particular small- scale schemes, usually require less sophisticated equipment for both construction and maintenance (unless pumps are used). The equipment needed is often easier to maintain and less dependent on the availability of foreign currency.
d. Previous experience with irrigation

• The choice of an irrigation method also depends on the irrigation tradition within the region or country. Introducing a previously unknown method may lead to unexpected complications. It is not certain that the farmers will accept the new method. The servicing of the equipment may be problematic and the costs may be high compared to the benefits.
• Often it will be easier to improve the traditional irrigation method than to introduce a totally new method.
e. Required labour inputs

• Surface irrigation often requires a much higher labour input for construction, operation and maintenance than sprinkler or drip irrigation. Surface irrigation requires accurate land leveling, regular maintenance and a high level of farmers’ organization to operate the system. Sprinkler and drip irrigation require little land leveling. System operation and maintenance are less labour intensive.
f. Costs and benefits

• Before choosing an irrigation method, an estimate must be made of the costs and benefits of the available options. On the cost side not only construction and installation, but also the operation and maintenance (per hectare) should be taken into account. These costs should then be compared with the expected benefits (yields). It is obvious that farmers will only be interested in implementing a certain method if they consider this economically attractive.