Sprinkler irrigation

In sprinkler irrigation the water is sprayed into the air and allowed to fall on the land surface in a uniform pattern. This method came into widespread use because it could be adapted to most sites and crops.

The advantages of sprinkler irrigation, properly installed and operated, are:

Erosion can be controlled. Safe irrigation is possible on land too steep for the efficient use of other methods.

Uniform application is possible on all kinds of soil. On sandy soils that have high intake rates, (1) sprinkler irrigation distributes water better than other methods do.

Land preparation is not required. More land is available for cropping. Field ditches, corrugations, and dikes are not needed.

Small streams of irrigations water can be used efficiently.

The limitations are: rather high initial cost of installation. Much water may be lost due to evaporation and wind.

A constant water supply is needed for the most economical use of equipment. The water must be clean and free of sand and debris.

Tight soils, which have slow intake rates, cannot be irrigated efficiently in hot, windy climates.

Three types of sprinkler systems are used to irrigated farm crops: rotating sprinkler heads, fixed jets, perforated pipes. (2) Rotating sprinkler – head systems are the more widely used type.

Each rotating sprinkler head applies water to a given area. This area is governed by the nozzle size and the water pressure. Sprinklers in the low – pressure range (3) have small area of coverage. Medium – pressure sprinklers (4) cover larger areas and have a wide range of precipitation rates. (5)

High – pressure sprinklers cover larger areas, and precipitation rates are higher than for the moderate or medium pressures.

The sprinkler system includes the pumping plant to provide needed pressure, the sprinkler, the riser pipe, the main pipeline, and the lateral distribution pipe. Sprinkler systems are classified as (1) permanent installations, with buried main and lateral lines, (2) semipermanent, with fixed main lines and portable laterals, and (3) fully portable systems.

Sprinklers with perforated pipes deliver water through very small holes, drilled at close intervals along a segment of the circumference of a pipe.

Electric motors and internal – combustion engines are used to drive the pumps.

Subirrigation

Subirrigation is a method of applying water beneath the ground surface. It is usually done by creating an artificial water table and maintaining it at some predetermined depth, usually 12 to 30 inches * below the ground surface for farm crops. Moisture reaches the plant roots through capillary movements. Application efficiencies (1) vary from 30 – 50 per cent in some areas up to 70 – 80 under favorable conditions.

Subirrigation requires permeable soil provided that the soil permeability in the rooting zone is homogeneous, and salinity is not a potential hazard. For successful subirrigation, an adequate supply of water of good quality must be available throughout the growing season. The topography must be nearly level and smooth.

A barrier against excessive losses through deep percolation must exist in the soil profile. The barrier may be a relatively impervious layer in the substratum. The distribution system must consist of a well - planned system of main ditch, field laterals, and structures, which will permit the water table to be raised to a uniform depth below the ground surface over the entire areas. An adequate outlet for the draige of the irrigated must be provided for, particularly in humid areas.

The principles involved in subirrigation are the same in all areas, although the means of introducing water into the soil profile may differ. An artificial water table is created over a natural barriers that prevents deep percolation of the water.

Water may be introduced into the soil profile through open ditches, through mole drains, or through tile drains. (2) The first way is most widely used because it is relatively inexpensive and is adapted to all the soil types that can be subirrigated. Mole and tile drains can be used in organic soil.

The main crops so irrigated are potatoes, beets, onion and corn. An effective drainage system has to be provided so that the water table can be lowered rapidly when necessary and harmful salts can be leached out of the profile.

The entire system, when adequately planned, installed, and maintained, provides excellent drainage during the rainy season.

Under limited situations, subsoil irrigation may be a very desirable system of irrigation. In general, however, it must be used with great caution. Danger from waterlogging and salt accumulation is great.