Crop yield response to water - Cra

about 55 days or more after planting, depending on genotype and environmental conditions.Rooting depth of tef grown in plastic tubes differs with genotype and ranges from 0.6 to 1.0m at heading (Mulu et al., 2001).As tef grain fills and approaches maturity, lodging is often a problem, especially if the grain isbountiful and there is strong wind and heavy rain. Tef is harvested when the vegetative partturns yellow or brown. Depending on the maturity group of the cultivar and photoperiod, tefmay be harvested between 60 and 150 days after sowing (Fufa et al., 2001).Water use & ProductivityIn Ethiopia, tef performs well with annual rainfall of 750-850 mm and 450-550 mm during itsgrowing season, but reasonable yield can be obtained with 300 mm of rainfall in its growingseason (Seyfu, 1997). There is very little reported research on its water productivity (WP)other than the first attempts to estimate normalized WP (WP*) of tef for use in AquaCropsimulations. The values arrived at in two studies (Araya et al., 2010; Alemtsehay et al., 2011)fell in the range of 14 to 20 g/m 2 , similar to values common for C 3 species but much lowerthan the 30 g/m 2 found for other C 4 species. The low WP* of tef is attributable at least partlyto low N fertilization, as the crop was fertilized with only 60 kg/ha of N, in both studies.The general WP* values noted above for C 3 and C 4 species are for crops grown with optimalmineral nutrition (receiving 150 to 250 kg N/ha). Additional and more definitive study of tefWP is much needed.Response to StressesTef is genetically diverse, grown at elevations of 1 000 to 2 500 m and a mean temperaturerange of 10°C to 27°C (Seyfu, 1997). The crop is considered to be tolerant to both drought andwaterlogging (Mulu et al., 2001). This feature is valuable to poor farmers in locations withhighly variable environmental conditions.With regard to water stress, at least one of the coping mechanisms is apparently osmoticadjustment. In a study (Mulu et al., 2001) with many genotypes, it was found that most of thetef lines osmotically adjusted by more than 0.4 MPa to slowly developing drought. However,under water stress canopy senescence is accelerated (Araya et al., 2010) as in most crops. Manycultivars require 200 to 300 mm of water during their early growth (NRC, 1996). Seyfu (1997)mentioned that 300 to 500 mm of rainfall is adequate in a growing season and even less than300 mm seasonal rainfall may be sufficient for early-maturing cultivars. This is the reason why tefis often planted after a cereal fails because of early drought, as a rescue crop in the same season,taking advantage of later rains to yield some grain and straw. Seasonal ET of early maturing tefestimated using AquaCrop or other simulation models for Ethiopian high lands would fall in therange of 280 to 300 mm. Hence, a short life-cycle tef may not even experience water stress insuch a situation, albeit the yield would be less compared to longer cycle cultivars.Tef grows on a wide range of soil types. To improve the yield where nutrients are limiting, onerecommendation is to apply phosphorus at the rate of 60 kg P 2 O 5 /ha at sowing to both lightand heavy soils, and 40 kg and 60 kg of nitrogen per hectare, respectively, to light and heavy240crop yield response to water