Crop yield response to water - Cra

The seasonal water requirements for barley depend on cultivar, target yield and cropmanagement. Malt barley requires better water management than food barley to meet thestandards set by the industry. During initial growth stages, crop water use ranges from 1 to 3 mm/day, rising to 5 - 8 mm/day after canopy approaches complete cover (usually at the appearanceof flag leaves), and remains high until the beginning of canopy senescence. Although winterrainfall is sufficient in many climates to supply the full barley water requirements in the earlyvegetative phase, effective rootzone soil moisture should not be depleted beyond 50 percentof total available water from emergence until flag leaf, after which depletions should probablynot exceed 60 percent of the total available soil water until the soft dough stage. Normally,with adequate winter rainfall, border or flood irrigation of malt barley will require 2 to 3irrigations on heavier soils corresponding with the critical growth stages. Light, sandy soilswould require more frequent irrigations.Excessive soil moisture during the jointing and boot stage, coupled with high nitrogen fertility,may promote vegetative growth that could result in lodging as the crop develops. Excessiveirrigation after the crop is well developed also promotes lodging.YieldBarley yields can vary from less than 1 to about 3 tonne/ha in water-limited rainfed conditionsto 4-10 tonne/ha in rainfed temperate (such as western and northern Europe) climates.Potential yields up to 12 tonne/ha have been observed. As discussed earlier, barley yield ismore sensitive to changes in growing conditions during the period when grain number is set,from stem elongation to just before the onset of grain filling. The cumulative growth duringthis phase is important enough to justify the assumption of some risk of frost at flowering;the sooner the flowering occurs the higher the crop growth throughout the phase from stemelongation to the onset of grain filling.Harvest index for barley is similar or only slightly lower than for wheat, and ranges from 0.45 to0.5 for modern cultivars under favourable conditions. As is the case for other cereals, the risein yield over time owes much to the rise in HI as the result of plant breeding. Interestingly,the increase in HI over time for barley has been somewhat slower than that for wheat andrice (Evans, 1993), possibly because of the grain quality constraints imposed by brewers. Thereis no simple, clear and unanimously accepted quality standard based on a set of variablesfor malt barley. Quality requirements represent a consensus of specifications commercialbrewers developed to ensure efficient production consistent with desired product propertiesor traditional methodologies (Savin and Molina-Cano, 2002), which vary with geographicalregions. However, protein content is regarded as one of the main quality attributes. In generalthere is a negative relationship between protein content and malting quality; the target is tokeep maximum grain protein content of malt barley around 10-12 percent.140crop yield response to water