Agriculture Reference
In-Depth Information
identified considerable genetic variability in TE for sorghum under controlled environments and
reported that TE can be improved through improving the biomass production. They further con-
cluded that identifying high TE genotypes based on biomass accumulation is a useful approach to
select for high TE in sorghum. These results widen the scope for improving TE or WUE through
exploiting traits or mechanisms that improve biomass production.
Important soil management practices that can improve WUE are conservation tillage, increased
soil organic matter content, reduced length of fallow periods, contour farming, furrow dikes, con-
trol of plowpans, crop selection, and use of appropriate crop rotation (Nielsen et al., 2002; Fageria
and Stone, 2013). It is possible to increase WUE by 25-40% through soil management practices that
involve tillage and by 15-25% by modifying nutrient management practices (Hatfield et al., 2001).
Also, precipitation use efficiency can be enhanced through the adoption of more intensive cropping
systems in semiarid environments and increased plant populations in more temperate and humid
environments (Hatfield et al., 2001).
Skip-row planting and tie-ridging can improve WUE in arid and semiarid environments.
Typically, the skip-row planting arrangement is one or two rows planted with 0.75 m spacing alter-
nating with one or two rows that are not planted (Mesfin et al., 2010). Similarly, tie-ridges typically
consist of interrow furrows of 20-30 cm depth that are blocked with earthen ties spaced accord-
ing to the slope of the land, water infiltration rate, and expected intensity of rainfall (Lal, 1977;
Gusha, 2002; Brhane et al., 2006). Clark and Knight (1996) observed increased grain yield with
skip-row planting of grain sorghum when the mean grain yield was <2 Mg ha
−1
, but decreased grain
yield when the mean grain yield was 3 Mg ha
−1
. On the High Plains of the United States, skip-row
planting of corn and grain sorghum was found to have a grain yield advantage compared with con-
ventional planting when the mean grain yield was <4 Mg ha
−1
and no disadvantage at 4-5 Mg ha
−1
(Mesfin et al., 2010). Increased evaporative loss of soil water with skip-row planting is a concern,
although saving more deep soil water for later in the season can compensate for these losses (Myers
et al., 1986). With skip-row planting, more soil water is out of reach of the plant roots until later into
the season when it gradually becomes available as the roots extend (Milroy et al., 2004). In northern
Ethiopia, Brhane et al. (2006) found a sorghum grain yield increase of 62% with tie-ridging com-
pared with flat planting. Highland pulse grain yield was increased with tie-ridging by 31-96% in
northern Ethiopia (Brhane and Wortman, 2008). Sanders et al. (1996) estimated that the adoption of
tie-ridging for small-scale sorghum production in Africa increased farm income by 12%.
In many arid and semiarid regions of the world, drought limits crop productivity (Habibzadeh
et al., 2013). Management practices that can provide support to plants to withstand water defi-
cits stress would improve crop production (Sylvia et al., 1993) and consequently N use efficiency.
Considerable evidence or research data are available to suggest that arbuscular mycorrhizal fungi
(AMF) have the potential to increase the tolerance of their host plants to water deficit stress
(Al-Karaki and Al-Raddad, 1997; Al-Karaki and Clark, 1998; Davies et al., 2002; Auge, 2004;
Habibzadeh et al., 2013). Arbuscular mycorrhizal symbiosis has been reported in 70-90% of stud-
ied land plants (Smith and Read, 2008). The pioneering studies of Allen and Boosalis (1983) indi-
cated a possible role of AMF hyphae in water uptake and transfer to host plants. AMF have been
shown to affect the water balance in plants under both well-watered and water-deficit stressed con-
ditions (Auge, 2001).
In addition, the use of crop species that requires less water can be an important strategy in a
water scarce environment. Table 8.9 shows the variation in WUE of principal food, vegetable, and
fruit crops under Brazilian conditions. It is very clear from the data in Table 8.9 that there is a large
variation in water use among crop species. In addition, WUE can also be improved by planting
drought-resistant crop species and genotypes within species. Sorghum and pearl millets are good
examples of drought-tolerant crop species. Sorghum is the fifth major cereal crop in the world in
terms of production and acreage. In addition, sorghum is one of the most drought-tolerant cereal
crops currently under cultivation (Blum, 2004) and radiation use efficiency (RUE) (Kiniry et al.,
1989; Muchow and Sinclair, 1994).
