Environmental Engineering Reference
In-Depth Information
of 5°C below freezing point; however, at temperatures lower than 5°C, plants are killed. Plants older
than 3 weeks are more susceptible and may die at 0°C. The crop can grow where available water
is between 360 and 500 mm and can respond positively to higher precipitation (Fribourg 1995).
Sorghum can reduce its water losses by its heavy wax cuticle, curling of its leaves, and its relatively
small number of leaf stomata (Gardner et al. 1981). When water supply is limited, sorghum has more
efficient water transport system than either corn or cotton (Ackerson and Krieg 1977).
Sorghum has a fibrous root system that grows rapidly in deep soils, and it is efficient as a water
forager. The adventitious root starts several weeks after emergence and extends rapidly up to 2 m
depending on the depth of soil wetting (Sullivan and Blum 1970). Graser (1985) compiled seasonal
water use of sorghum at several locations from 1976 to 1981 and reported a range of 179-540 mm
under dry-land and 321-645 mm under irrigated conditions depending on the length of the growing
season. Erie et al. (1981) reported that consumptive water use increases with plant growth, reaches
a peak, and then decreases by harvest time. Water use of sorghum was found to be greatest during
the boot and soft dough stage and lower during the seedling, tillering, and ripening stages (Porter
et al. 1960). Several factors including temperature, precipitation, solar radiation, humidity, wind
movement, and hybrid affect sorghum water-use efficiency. The water-use curve in any one year
or at any site will vary from the long-term average because of changes in some of the factors listed
above. Water-use efficiency ranging from 13 to 29 kg/ha per mm has been reported in the literature
under dry-land and irrigated conditions (Hedge et al. 1976; Sivakumar et al. 1979). The crop has
the ability to delay development under water stress during the vegetative growth stages and resume
growth when water conditions improve. This drought avoidance mechanism works well under
tropical and subtropical conditions with a long growing period. However, this mechanism of drought
resistance may result in poor yield because of prolonged drought, insufficient season length, or when
it occurs at critical growth stage. Field water capacities of 25-50% and temperatures above 28°C are
most favorable for optimal sorghum germination (Fawusi and Agboola 1980). The favorable mean
temperature for sorghum growth is approximately 37°C, and the minimal temperature for
growth
is 15°C (Cothren et al. 2000).
19.2.5 c
rop
u
SES
Sorghum is one of the top five cereal crops in the world, along with wheat, oats, rice, corn, and bar-
ley. Worldwide more than 40 million ha are planted to sorghum. It is a genus with many species and
subspecies, and there are several types of sorghum, including grain, forage, and sweet sorghums.
Therefore, sorghum is extremely versatile in offering multiple pathways to ethanol.
• Starch-to-ethanol
: Grain sorghum conversion to ethanol is equal to corn. Today, approxi-
mately 28% of the U.S. grain sorghum crop currently goes into ethanol production accord-
ing to industry estimates.
• Sugar-to-ethanol from sweet sorghum
: The conversion efficiency is similar to that of
sugarcane.
• Cellulosic ethanol
: No other crop or other cellulose source equals sorghum in conversion,
production efficiency, or ethanol gallons per acre.
19.3 GraIn sorGhums
Grain sorghums include what are commonly known as kafir, kafir corn, durra, and milo. Grain
sorghum has been bred to produce approximately 2- to 5-ft height to facilitate harvesting with
standard grain harvesters. Grain sorghum has a wide variety of uses that includes food for
humans, feed for livestock, alcohol production, and industrial uses. Sorghum can be sorted into
grain sorghums, forage sorghums, and sweet sorghums (Rooney and Serna-Saldivar 2000). Grain
sorghums often are short and can be mechanically harvested whereas forage sorghums are tall and
