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14 Chapter 3. Constituents of irrigated agricultural systemWater circulation is the manner in which water is conveyed from the sourceto the plots. It refers to:• type of water distribution: on demand or rotation, intervalbetween irrigations, permanent (24 h/24 h) or impermanent waterdistribution;• water conveyance: cross section, slope, discharge capacity and canalconstruction (earthen or lined canals, compaction); or characteristicsof pipe distribution;• type of water partition, water control and measurement structures.Layout is the manner in which individual canals and plots are linked in space.This important sub-constituent should make the link between a large numberof factors, such as:• the size of the secondary and tertiary units in connection with thenumber of plots, the “main d’eau” (discharge at plot level), irrigationintervals and topography.• the various types of soil and other land utilizations: roads, cattlebreeding, forests, and inhabited areas.Water circulation and layout are closely linked and interact with each other.Changes brought to one automatically lead to changes to the other one withthe risk of damaging the cohesion of the whole irrigation scheme.Plot usePlot use includes all the agricultural techniques implemented by farmersand the outputs of their irrigated plots. Usually the cropping system onirrigated plots is a choice made at farmers’ household level in relationto other farming and, sometimes, non-farming activities. The head ofhousehold makes decisions regarding labour, inputs and capital allocationwith due consideration to the various constituents of the family’s wholeproduction system.Characteristics of plot use:Agricultural practices and production:• type of crops or associations of crops and crop rotation;• crop production process for one crop from soil preparation to harvest;• yields of products and by products.