What is the most appropriate irrigation method

Key issues capital v. recurrent costscapital v. recurrent costs salinisation risk,salinisation risk, uniformity,uniformity, minimisation of wastage and use of waterminimisation of wastage and use of water minimising labour costs and increasing automation if labour costminimising labour costs and increasing automation if labour cost

Topography  If uniform slopes and not too steep, surface methods OK methods OK  If topography undulating - use sprinkler or drip methods methods  Surface methods cannot be easily used on farms with rocky or sandy soil, steep slopes, badly with rocky or sandy soil, steep slopes, badly breaking hills or gullies breaking hills or gullies  Land grading needed for good surface irrigation  Land levelling is expensive - if too much is required it may be cheaper to use sprinklers or required it may be cheaper to use sprinklers or drip irrigation drip irrigation  Even with relatively flat land subsoil can become exposed and crops can be very variable exposed and crops can be very variable

Soil types  Low AWCs require frequent light irrigations & sprinklers or other overhead methods might be better  High infiltration may lead to high losses from percolation if surface methods used so sprinklers or drip best.  Otherwise, short fields required -> increases labour costs, wastes land (head land/roads, mechanisation problems (e.g turning)  If soils very variable (heterogeneous), easier to adapt sprinkler or drip types.

Effect on Soil Surface irrigation tends to encourage erosion and leaching of nutrients. In sprinkler irrigation, though poor design can cause compaction and sealing, proper application eliminates erosion, compaction, sealing, and leaching

Water table Irrigation efficiency of surface irrigation always lower than overhead. If high water table (<4 m), drains will be required. This is expensive. In this case, better to use sprinklers or drip as there will be less percolation. Better control possible with overhead or drip systems usually, underground drains will not be needed.

Water Losses Surface irrigation loses water through porous ditches, deep percolation, run-otf. and evaporation Sprinklers and drip lose water mainly through evaporation Sprinklers requires 15 to 60% less water than surface methods Irrigation Efficiency(water used by plant as % of applied water) is % for surface methods, per centfor sprinklers and even higher for drip irrigation

Water availability If in short supply (or expensive), use sprinklers or drip - or make sure canals lined and management is v. good Land availability Sprinker or drip systems have less loss of land to irrigation structures such as ditches, canals, etc

Water quality Sprinklers / drip cannot be used directly if sediment or sewage in water - though sediment can be removed with filtration equipment If soil is saline, leaching is often cheaper using surface irrigation. But if WT is saline - less likely to rise with sprinklers / drip

Climate If wind > 15 to 20 kph - do not use sprinklers (distortion of distribution pattern) Heavy rain in irrigation season may exacerbate problem of mechanised cutlivation -> sprinklers or drip Crop Tall (e.g. sugar cane) - difficult to move pipes If susceptible to moisture stress - surface least suitable (intervals between irrigations usually longer) Can use sprinkler or drip for most crops except rice

Crop Germination Surface irrigation tends to be slower than sprinkler or drip irrigation - light, even applications of water

Operating conditions If history of surface irrigation - may be more likely to succeed than sprinkers, e.g. Gezira, Sudan Sprinker systems can make do with less experienced labour than for surface irrigation. Scheduling easier and distribution more even with non-surface methods What are local resources for mechanised or pump dependent systems

Financial aspects - very site specific Surface systems have low yields to start (levelling) If short pay-back period required -> sprinklers / drip Running costs of surface schemes usually less than sprinkler / drip schemes Capital costs vice versa if dam and canals required & costs included. If not, cost of surface irrigation may be less than sprinkelrs on level, medium textured soils Sprinkler systems are cheaper on rougher, lighter soils Land value increased for surface and overhead irrigation

Labour Requirements Surface irrigation requires from one-half to one person per acre where land lays well Sprinkler systems require about half that of surface methods

Mechanisation For sprinker irrigation, lack of furrows or corrugations means less wear and tear on farm machinery and faster farming

Other considerations Sprinkler systems can be used for fire protection, frost protection, fertilising, dewatering (drainage), etc.