Agriculture Reference
In-Depth Information
not be able to advance food security with conventional sources of water. While the
excessive use of water (traditional flood irrigation) must be avoided, nonconventional
sources must also be identified. For example, growing a rice paddy under flooding
condition in hot and arid environments is wasteful use of scarce water resources.
Such an excessive use of water in cropland must be avoided by judicious water use,
water conservation in the root zone, water harvesting and recycling, and micro-
irrigation (e.g., drip subirrigation and fertigation). Rice, a semiaquatic food staple
of a large population, consumes a large amount of water when grown under flooded
conditions. There is a need to improve water management practices in rice-based
cropping systems. The so-called aerobic rice can be grown, with appropriate variet-
ies and weed control measures, under nonflooded soil environments (Gaydon et al.
2012).
Asia, including China and countries within the Indian subcontinent, is faced with
numerous challenges of high population, limited arable land area, and scarcity of
water resources. The problem of finite natural resources is confounded by the deg-
radation of soil, pollution and contamination of water, and loss of forest and other
vegetation cover. Under these scenarios, the high potential of elite varieties can be
realized only if grown under optimal soil conditions. Water scarcity is a serious
issue, and policy makers and researchers must realize that adoption of BMPs is futile
when water availability in the root zone is scarce (Tyagi et al. 2012). Furthermore,
the key to effective water resource management is the strong understanding of the
close link between the hydrologic cycle and the soil management and that the choice
of any BMP for soil management implies specific water requirements (Bossio et al.
2010). The water productivity can be enhanced by restoration of degraded soil and
improvement of SQ in relation to SOC concentration, nutrient availability, and soil
structure and tilth. Effectiveness of NT farming also lies in its capacity to conserve
water in the root zone and enhance WUE (Lafond et al. 2006).
The global economy and the attendant increase in food trade have also high-
lighted the importance of nonconventional water resources and the so-called virtual
water. Important issues among nonconventional water resources for crop production
include desalination of sea and brackish groundwater, rainwater harvesting (from
land and roofs of the buildings), use of agricultural drainage water, wastewater from
industrial and urban uses, and so forth. Linking rivers to physically transfer water
from one watershed to another is also an option (Qadir et al. 2007) that involves seri-
ous engineering, and political and logistical considerations. These practices involve
conversion of blue and gray water into green water.
The term “virtual water” implies the water used to produce the food that is
imported into water-scarce countries. It refers to the amount of water needed to
locally produce the food that has been imported into the country. Thus, “virtual
water” plays an important role in the international trade for food among countries
with water surplus and deficit. Because of involved subsidies, any assessment of the
magnitude of virtual water must also consider policies and incentives of the food-
exporting countries. Globally, 131 out of 146 countries are involved in some virtual
water trade, with an attendant increase in the gross arable land areas (Kumar and
Singh 2005). It is also recognized that virtual water often flows out of water-poor,
land-rich countries to land-poor, water-rich countries, accentuating the challenges
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