Crop yield response to water - Cra

two cereals are scarce, one of the main differences is that barley is generally believed to bebetter adapted than wheat to stressful situations and therefore it is normally sown in harsherenvironments than wheat (see Cossani et al., 2009). In many areas, where one crop is producedper year, barley is grown in rotation with a variety of other winter annuals such as other cereals,oilseed crops, and pulses; but in dry environments barley monoculture is common (i.e. in theMediterranean basin in areas where annual rainfall is less than 350 mm). The season length ofbarley tends to be shorter than that of wheat, making it more suitable for double cropping. Forinstance, barley may be followed immediately by either maize or soybean.Growth and DevelopmentBarley genotypes are generally grouped into two categories according to their sowing time:winter and spring cultivars. Winter barley is sown in autumn and requires a cold period(vernalization) during early growth for flowering under long days, and matures in latespring to early summer. This ensures flowering when the risk of late frost is low, leading toa long yield formation period that maximizes potential yield. In areas where winter is harshenough to kill a significant number of seedlings, instead of winter barley, spring barley,not requiring vernalization, is sown in the spring when soil temperatures are adequate forgermination and seedling emergence and it is also photoperiod sensitive. Because of themuch shortened duration in the field, spring barley has lower yield potential than wintertypes. In environments with quite mild winters, winter type may be sown in the middleof winter and still flowers (mid-spring) and matures (early summer) under favourableconditions to give yields similar to those obtained when winter types are sown in autumn.This practice of sowing winter types late is traditional for much of the barley growingregion of the Mediterranean Basin, particularly in North Africa, and the cultivars can betermed Mediterranean genotypes. They are usually facultatively sensitive to vernalization(facultative barleys). It is generally accepted that within the normal growing season a delayin sowing date has a negative effect on grain yield. The season length of a spring typeranges from 90 to 130 days while a winter type needs about 180 to 250 days to mature, andMediterranean types are intermediate. Samples of duration of various growth phases aregiven in Table 1.Table 1Sample duration (calendar days) of different stages of Mediterranean, springand winter barley from the literature. Data are averages of different cultivars.Barley typeSowingemergenceSowingheading*SowingmaturityMediterranean 10-12 107-118 137-150Spring 10-14 45-52 91-96ReferenceAbeledo et al., 2003;Abeledo, 2009 unpublishedMuurinen et al., 2007;Peltonen-Sainio, P., pers. Comm.Winter,Southern Europe14-16 144-169 172-212Albrizio et al., 2010;Cossani et al., 2009Winter,Northern Europe- 225 280 HGCA, 2006*pollination in barley, unlike in wheat, occurs at heading136crop yield response to water