Crop yield response to water - Cra

ox 8 Spatial relation between the distribution of water over a field and its area.The Figure shows a simplified diagram of the spatial distribution of irrigation depth,X, as a function of fractional irrigated area. The two straight lines represent thehypothetical relationships between the depth of water applied (X, normalized withrespect to the required depth to refill the soil water deficit prior to irrigation) as afunction of the fraction of the irrigated area. The two inclined lines represent thedistribution of water for full and for deficit irrigation. Note that under full irrigation,50 percent of the area receives water in excess of the required depth, X R , needed torefill the root zone. The slope of the line represents the degree of uniformity; thesteeper the slope, the less uniform the irrigation application would be.Normalizedirrigationwater (X)0Deficit irrigationX R1OverirrigationFull irrigationDeficit200.25 0.50 0.751.00Fraction of irrigated areaPeriodic monitoring of irrigation uniformity is an important component of a good irrigationmaintenance programme.IRRIGATION SCHEDULINGBackgroundThe goal of irrigation scheduling is to determine how to supply the tree or vine with thecorrect amount of water at the appropriate time. Irrigation is applied to avoid tree waterdeficits that are not compatible with management objectives. The usual objective of themanager is to maximize net economic benefit, which does not always coincide with maximumyields, as when deficit irrigation can improve fruit quality and thus crop value. Most growersmake irrigation decisions based on their practical experience and consider the practicallimitations of their systems. Research has developed technical scheduling procedures tooptimize orchard water management. Technical procedures are adopted by growers who270crop yield response to water