Crop yield response to water - Cra

thinning. As mentioned, excessive nitrogen, especially late in the season, encourages excessiveleaf growth and reduces sugar concentration of the beet. Fertilizer applications may be up to150 kg/ha N, and 50 to 70 kg/ha P 2 O 5 and 100 to 160 kg/ha K 2 O at planting.Except for during the early growth stages following stand establishment, the crop is quitetolerant to salinity (Katerji et al., 1997). Yield decrease is 0 percent at an EC e of 7 dS/m, 50percent at EC e of 15 dS/m, and 100 percent at EC e of 24 dS/m. During early growth EC e shouldnot exceed 3 dS/m.Irrigation practiceAbout one-fourth of the world’s 4.2 million ha of sugar beet receives irrigation, but thefraction varies greatly from region-to-region. In the United States, Eastern Mediterranean,Iran and Chile between 80 and 100 percent of the sugar beet area is irrigated; in the westernMediterranean irrigated area amounts to 20-80 percent of total, while in Central and NorthernEurope, it is less than 40 percent. In most sugar beet growing areas of the world irrigation issupplemental and typically only 100-200 mm are needed. In other areas (United States, Egypt,Pakistan) irrigation is essential for beet production and 500-1 000 mm are commonly applied.Practically, all irrigation methods are used for sugar beet, mainly sprinkler (pivot, booms), butalso surface irrigation, and in rare cases, even drip irrigation.When water supply is limited but land is not, water should not be used to meet the full waterrequirement of the crop. Instead irrigation should cutoff earlier and the water saved used toexpand the area cropped. This is because the efficiency of water utilization for sucrose yieldincreases when water is restricted near harvest, for reasons already discussed. Under thoseconditions, harvest index increases significantly over the value achieved under full irrigation.YieldA good commercial yield of 160 to 200 days sugar beet is 40 to 60 tonne/ha of fresh beet.Under very favourable conditions yields of up to 100 tonne/ha or more have been obtained.Total dry matter production varies from less than 10 tonne/ha to more than 20 tonne/ha.Sucrose content varies, mainly between 14 and 18 percent on a fresh mass basis, correspondingto sucrose yields of 5 up to 15 tonne/ha. WP sucrose/ET varies from 0.9 to 1.7 kg/m 3 .Harvest index (HI) for sugar beet is best defined as the ratio of sucrose produced to biomassof the storage root and shoot. Biomass of fibrous roots is neglected because most studies donot attempt to measure it. Also, shoot biomass is often not measured. On the assumption thatstorage root biomass is four to eight times the shoot biomass, HI in terms of sucrose producedwould commonly fall in the range of 0.4 to 0.55, although values outside of this range arealso encountered in the literature. HI tends to decrease when conditions favour luxuriousvegetative growth, mainly high nitrogen and high water supply, especially as the harvestingtime approaches. Extending the harvesting time to later in the season usually enhances HI,but only up to a point.SUGAR BEET 207