369Khashoei 2003 ; Barzegar et al. 2002a, b), Inceptisols (Ishaq et al. 2001 ) and Alfisols
(Smith et al. 1992 ). In addition to crusting, Alfisols in central India are also prone to
hard setting (Smith et al. 1992 ).
The principal constraints to enhancing crop production on Alfisols, which occur
extensively in southern Asia, are: (i) low SOC pool, (ii) poor soil structure, (iii)
crusting and mechanical impedance, (iv) high runoff and erosion, (v) high soil tem-
peratures, (vi) severe drought stress, and (vii) low soil fertility (Lal 2006 ). In India,
Alfisols occur mainly in southern parts of the country and constitute about 30 % of
the soils under rainfed farming. Being light-textured and shallow, their available
water capacity (AWC) is low. Furthermore, hard setting and structural instability
exacerbate surface sealing and crusting. These soils in semiarid climates support a
single rainy season crop (Kharif or summer) with productivity levels of 0.7–0.8 Mg/
ha. These soils are characterized by low SOC and N stocks despite large variations
in the cropping system, soil type, rainfall, temperature and supplementary manage-
ment practices such as manuring and fertilization (Srinivasarao et al. 2012b). The
high clay content, high waterholding capacity and favorable moisture release char-
acteristics are important attributes of Vertisols which reduce the severity and dura-
tion of drought under conditions of low and erratic rainfall. These soils have
numerous constraints especially low infiltration rates, poor internal drainage, inun-
dation, high runoff and erosion, poor trafficability, narrow workable water content
range, high evaporation, shrinkage cracks and risks of salinization. Similarly, allu-
vial soils (Inceptisols and Entisols), dominant in the Indo-Gangetic Plains, are light-
textured (sandy and sandy loams), have low SOC concentrations and low inherent
soil fertility. Crusting and high soil strength are serious problems on alluvial soils in
arid regions (140–180 mm rainfall), which adversely affect seedling emergence and
the crop stand. High crust strength reduces the emergence of cotton in Pakistan
(Nabi et al. 2001 ) and elsewhere. However, Inceptisols respond to inputs (e.g., irri-
gation, fertilizers) and are highly productive under irrigated conditions. Arid cli-
mate prevails over 32 Mha of land area in seven states of India alone. Surface
crusting, low water and nutrient retention capacity, drought stress, subsoil salinity
and wind erosion are severe constraints to achieving high yields.
3.2 Climate Change
South Asia is home to more than one-fifth of the world’s population and is the most
natural disaster-prone region in the world. The high rates of population growth and
natural resource degradation, with continuing high rates of poverty and food insecu-
rity, make South Asia one of the most vulnerable regions to the impacts of climate
change. In general, past and present climate trends and variability in South Asia can
be characterized by increasing air temperatures, which are more pronounced during
winter than in summer. There has been an increasing trend in the intensity and fre-
quency of extreme events such as heat waves, cold waves, untimely and
Dryland Agriculture in South Asia: Experiences, Challenges and Opportunities