Crop yield response to water - Cra

Barley development may be thought of as occuring in three phases, vegetative, reproductiveand grain filling. During vegetative phase all leaves are initiated and then emerge continuouslyuntil the final leaf emerges. Tillers are initiated after leaf 3-4 emerges from nodes on themain shoot and continues until stem elongation. During the reproductive phase, spikeletdifferentiation starts in the apex and continues with the development of floret primordiawithin previously differentiated spiklelets and finishes with the determination of fertileflorets. During the second half of the reproductive phase the stems, and later the spikes,grow rapidly while some tillers die and some of the initiated spikelets do not progress intheir development towards a fertile spikelet at heading. During this period dry matter of thejuvenile spike is accumulated and this growth of the spike is related to the survival of floretand spikelet primordia. This is the reason why there is a close relationship between grainnumber per unit area and the dry weight of the heads at anthesis (Prystupa et al., 2004),provided there is no post anthesis stress. Barley florets are self-pollinating and anthesis startsas the head emerges from the flag leaf sheath.In the grain-filling phase, grains accumulate dry matter up to their final grain weight. Again,if assimilates are limiting, some of the potential grains may be aborted early or fail to developfully.The major environmental factors affecting barley phenology are temperature and photoperiod.As for all crops, temperature affects the rate of progression through the various phases, andis accounted for when AquaCrop is run in the growing degree day (GDD) mode. The basetemperature and upper temperature for barley should be similar to that of wheat, 0 o C andaround 25 o C, respectively. Another key temperature effect is on vernalization, which requirescold temperature. Vernalization, together with photoperiod, largely determines the time ofheading and flowering of winter cultivars. Figure 3 shows typical development of a barleyplant, illustrating the particular developmental phases.Plant density is a management practice that modifies the crop canopy size and development,and hence ability of the crop to capture photosynthetically active radiation. As for othertemperate cereals with tillering habits, plant densities may range widely, with low densitybeing compensated for by more tiller formation. For this reason, planting densities arenormally higher for spring than for winter or Mediterranean type. Actual sowing rates aimto establish stands of 50 to 300 seedlings/m 2 , with most common densities being between150 and 250 plants/m 2 for temperate zone with adequate rainfall. For rainfed semi-arid andarid areas, the sowing rates would be at the low end of the range. Row spacing is typicallybetween 0.15 and 0.25 m. When barley is grown as a forage crop, the optimum plant densityis higher than that for grain production.The pattern of root growth can be described as exponential between sowing and the onsetof stem elongation (when more assimilates are used for stem and spike growth), and thencontinues some past anthesis. Maximum rooting depth can vary from 0.30 m in shallow soilsto more than 2 m on deep sands and loams. Root growth patterns are strongly modified byfertilizer locations in the soil and soil moisture conditions. Barley, like wheat, can grow on awide range of soils from deep sands and shallow soils to loams to heavy clays.barley 137