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Suitability of spray irrigation



Methods of spray irrigation vary substantially, but die typi­cal applications for spray irrigation, and its advantages and disadvantages, follow:

Topography.Spray irrigation can be successfully used on sites where ex­cessive earthmoving would be required to initiate a surface irrigation system. On sloping sites, however, runoff can be a problem if die spray application rate exceeds die infiltration rate of die soil. On steeper sites, additional problems of pres­sure variation and die tracking of self-propelled machines can arise.

Soil conditions.Application rates from sprinklers can be more closely matched to soil infiltration rates by appropriate selection of nozzle sizes and operating pressures. This makes spray irrigation more suited to soil types where application by surface irrigation becomes inefficient such as on light soils or very heavy soils.

Shallow soils where even moderate earthmoving for sur­face irrigation may expose the subsoil, may be irrigated with low application sprinklers.

Where crusting of soil is a problem, impact by droplets on bare soil may exacerbate the condition.

Water supply.Spray irrigation may make better use of limited water supplies, compared to surface irrigation, because of a higher degree of control over volume and depths of water applied. (This advantage is even greater with microirrigation methods.) Such control makes spray irrigation more suitable for germination and emergence of seeds and seedlings, provided crusting created by droplet impact is avoided. Distribution and reticulation losses are minimised in a piped system, compared to die open channels typical for surface irrigation. On die other hand, wind drift of spray droplets can severely interrupt the uniformity of application from sprinklers and reduce application efficiency. Sprinklers apply water typically over the whole crop canopy, which will increase canopy humidity, and may cause problems of accelerated fungal attack and deposition of any dissolved salts onto foliage. However, spraying irrigation water over die crop canopy may provide secondary benefits of dust control and cooling benefits.

System management.Manual shifting of spraylines or irrigation machines often contributes a significant portion of the cost of operation. Labour can be reduced with self-propelled machines, which are more easily managed man a channel/flood system. The equipment must remain operational in wet and/or cultivated soil.

The design capacity of a spray irrigation system sets a limit for the application rate and turnaround time of die equipment. Consequently some spray irrigation systems have dif­ficulty coping with extreme conditions of water demand, par­ticularly when strong winds disturb wetting patterns.

Spray irrigation systems better utilise restricted growing areas, compared to surface irrigation, by not requiring pro­ductive land be used for supply channels, headlands, recirculation works, and so on.

Other features.Spray irrigation can be used, with adaptation, for frost pro­tection in marginal frost conditions. The continuous applica­tion of water to the plant surface prevents die cell liquid freezing. (If misting or fogging is used, heat loss by radiation is reduced, also aiding in frost protection.)

Chemicals can be easily injected into a piped reticulation system, particularly fertilizers, but this can also be accom­plished with other methods of irrigation.

Spray irrigation of effluent is feasible, as it is by other irri­gation methods.

Spray irrigation equipment is better adapted to fire pro­tection than other methods.




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