Describe the detailed classification of water application methods.

• Based on energy/pressure reqd

Gravity Irrigation. Border, basin & furrow irrigations

Pressurized irrigation. Drip & Sprinkler irrigations

• Based on placement of irrigation water (on, above or below soil surface)

Surface irrigation. Border, basin & furrow irrigations

Subsurface irrigation

Overhead irrigation. Sprinkler & hand watering

• Based on wetted area of crop root zone by irrigation

Flood irrigation (Border, basin & furrow)

Drip (or trickle or localized) irrigation

Sprinkler irrigation

Surface Irrigation Method: Borders

• Best adapted to grain and forage crops
• Good for uniform soils with mild slope
• Not good for crops sensitive to wet soil conditions
• Typical efficiencies range from 70 – 85%
• Major investment is that of land grading or leveling
• Border strip width, W = 3 – 30m; Length, L = 100 —- 800m
• Has zero side slope and uniform longitudinal slope of <1%
• Strips have no cross slope

Surface Irrigation Method: Basins

• Field is divided into small units surrounded by levees or dikes
• Basin size: 1 to 15 ha; up to 100 to 400 m long
• Most commonly practiced for rice and orchard tree crops
• Level basin

1. Water is held until it infiltrates or is drained away
2. Minimum runoff loss and High application efficiency is possible

• Graded basin (contour levee irrigation)

1. Constructed with two levees parallel and two perpendicular to the field contours
2. Water enters along the upper contour and flows to the lower.

Advantages

• Water covers the basin rapidly to ensure good uniformity
• Best suited for lands/crops where leaching is required to wash out salts from the root zone
• Involves the least labour of the surface methods
• Design efficiencies can be on the order of 70-85%
  

Limitations

• Levees interfere with movement of farm equipment
• Higher amount of water is required compared to sprinkler or drip irrigation
• Amajor cost in basin irrigation is that of land grading or leveling
• Impedes surface drainage

Surface Irrigation Method: Furrow

• Irrigation is accomplished by running water in small channels (furrow)
• Constructed with or across the field slope
• Water infiltrates from the bottom and sides of furrows moving laterally and downward to wet the soil and to move soluble salts, fertilizer and herbicides carried with the water
• Widely spaced row crops such as potato, maize, vegetables, and trees
• Loam soil with mild slope, 0.5-2%
• Labour reqd is generally higher
• Major initial cost is construction of furrow

Types

1. Level
2. Graded
3. Contour

Advantages

• Efficiency can be high.as 90%
• Developed at a relatively low cost after necessary land-forming activities are accomplished
• Erosion is minimal
• Adaptable to a wide range of land slopes

Limitation

• Not suitable for high permeable soil where vertical infiltration is much higher than the lateral entry
• Higher amount of water is required, compared to sprinkler or drip irrigation
• Furrows should be closely arranged

Sprinkler Irrigation

• Water is delivered through a pressurized pipe network to sprinklers, nozzles, or jets which spray the water into the air, to fall to the soil as an artificial “rain”
• Light sandy soils are well suited
• Sprinklers can be used on any topography
• Sometimes used to germinate seed and establish ground cover for crops like lettuce, alfalfa, and sod
• Very high efficiency water application
• High capital investment but has low labor requirements

Types

1. Portable or hand move
2. Solid set & permanent
3. Travelling gun system
4. Side roll system
5. Centre pivot & linear move system

Advantages

• Readily automatable
• Facilitates to chemigation and fertigation
• Reduced labor requirements needed for irrigation

Limitations

• Many crops (citrus, for example) are sensitive to foliar damage when sprinkled with saline waters
• Initially high installation cost
• High maintenance cost

Drip Irrigation

• Constant steady flow of water is applied directly to the root zone of the plants by means of applicators operated under low pressure
• Applicators: orifices, emitters, porous tubing, perforated pipe
• Most efficient irrigation system
• Most suited to high-density orchards, tree crops, and high-value horticultural crops
• Not designed for large root systems
• Suited for situations where the water supply is limited
• Very effective in applying nutrients (fertilizers)/insecticides through the drip system
• Burying the drip system reduces water loss even further by preventing runoff across the surface

Advantages: 

• Highly efficient system
• Limited water sources can be used
• Right amount of water can be applied in the root zone
• It can be automated and well adapted to chemigation and fertigation
• Reduces nutrient leaching, labor requirement, and operating cost
• Nearly uniform distribution of water
• Lower pressures are required-low energy for pumping

Limitations:

• High initial cost
• Technical skill is required to maintain and operate the system
• The closer the spacing, the higher the system cost per hectare
• Damage to drip tape may occur
• Cannot wet the soil volume quickly (to recover from moisture deficit) as other systems
• Facilitates shallow root zone
• Needs clean water

Other Forms of Irrigation

Hand watering

• Nurseries and Fruit trees

Capillary irrigation

• Wet the root zone by capillary rise
• Buried pipes or deep surface canals

Localized irrigation

• Water is applied around each or group of plants
• Wets root zone only

Subsurface irrigation

• Water is applied below the ground surface either by raising the water table within or near the root zone or by using a buried perforated or porous pipe system