Rice (Oryza sativa L.), a staple food for more than half of the world population, is commonly grown by transplanting seedlings into puddled soil (wet tillage) in Asia. This production system is labor-, water-, and energy-intensive and is becoming less profitable as these resources are becoming increasingly scarce. It also deteriorates the physical properties of soil, adversely affects the performance of succeeding upland crops, and contributes to methane emissions. These factors demand a major shift from puddled transplanting to direct seeding of rice (DSR) in irrigated rice ecosystems. Direct seeding (especially wet seeding) is widely adopted in some and is spreading to other Asian countries. However, combining dry seeding (Dry-DSR) with zero/reduced tillage (e.g., conservation agriculture (CA)) is gaining momentum as a pathway to address rising water and labor scarcity, and to enhance system sustainability. Published studies show various benefits from direct seeding compared with puddled transplanting, which typically include (1) similar yields; (2) savings in irrigation water, labor, and production costs; (3) higher net economic returns; and (4) a reduction in methane emissions. Despite these benefits, the yields have been variable in some regions, especially with dry seeding combined with reduced/zero tillage due to (1) uneven and poor crop stand, (2) poor weed control, (3) higher spikelet sterility, (4) crop lodging, and (5) poor knowledge of water and nutrient management. In addition, rice varieties currently used for DSR are primarily selected and bred for puddled transplanted rice. Risks associated with a shift from puddled transplanting to DSR include (1) a shift toward hard-to-control weed flora, (2) development of herbicide resistance in weeds, (3) evolution of weedy rice, (4) increases in soil-borne pathogens such as nematodes, (5) higher emissions of nitrous oxide—a potent greenhouse gas , and (6) nutrient disorders, especially N and micronutrients. The objectives of this chapter are to review (1) drivers of the shift from puddled transplanting to DSR; (2) overall crop performance, including resource-use efficiencies of DSR; and (3) lessons from countries where DSR has already been widely adopted. Based on the existing evidence, we present an integrated package of technologies for Dry-DSR, including the identification of rice traits associated with the attainment of optimum grain yield with Dry-DSR.

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Direct Seeding of Rice: Recent Developments and Future Research Needs

https://www.uvm.edu/giee/pubpdfs/Fisher_2007_Ecological_Economics.pdf

Poverty and biodiversity: Measuring the overlap of human poverty and the biodiversity hotspots

Countering the widely held opinion that water scarcity entails prime risks of international conflicts over shared water resources, it is argued that the risk of conflicts within countries in fact is larger, and that the risk of international conflict is derived from the necessity to avoid what is defined as second-order conflicts within countries, caused not by water scarcity itself, but by the institutional change required to adapt to water scarcity. To illustrate this, the most pernicious effect of social resource scarcity, a new Social Resource Water Stress/Scarcity Index (SWSI) is developed, built on a combination of traditional hydrological indices and the UNDP Human Development Index as the most readily available proxy for social adaptive capacity. Calculations are made for 159 countries, 1995 and with projections to 2025. The study demonstrates that the index captures the social impacts of water scarcity more accurately than earlier indices.

Water conflicts and social resource scarcity

Water in food production and processing: quantity and quality concerns

Metrics of water scarcity and stress have evolved over the last three decades from simple threshold indicators to holistic measures characterising human environments and freshwater sustainability. Metrics commonly estimate renewable freshwater resources using mean annual river runoff, which masks hydrological variability, and quantify subjectively socio-economic conditions characterising adaptive capacity. There is a marked absence of research evaluating whether these metrics of water scarcity are meaningful. We argue that measurement of water scarcity (1) be redefined physically in terms of the freshwater storage required to address imbalances in intra- and inter-annual fluxes of freshwater supply and demand; (2) abandons subjective quantifications of human environments and (3) be used to inform participatory decision-making processes that explore a wide range of options for addressing freshwater storage requirements beyond dams that include use of renewable groundwater, soil water and trading in virtual water. Further, we outline a conceptual framework redefining water scarcity in terms of freshwater storage.

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The measurement of water scarcity: Defining a meaningful indicator

This Population Action International report re-estimates projected water supplies by 2050 in accordance with revised 1996 UN population projections. The report summarizes the causes and consequences of water scarcity and explains the importance of slower population growth. Water scarcity issues will depend in part on how rapidly population grows. Current estimates update a 1993 report. 400 million to 1.5 billion fewer people will live in water shortage countries by 2050 than had been previously projected. The improved scenario does not eliminate the concern about renewable freshwater scarcity for many millions. Currently over 430 million people live in countries experiencing water stress. By 2050 the percentage of people living in water-stressed countries will increase three- to five-fold. Data on population growth were obtained from "UN World Population Prospects: the 1996 Revision"; data on water supplies from "World Resources 1996-97: A Guide to the Global Environment." This revision is necessary because world population growth is slowing more dramatically than previously expected. Larger population size is the most significant human influence on the availability of fresh water. A Swedish hydrologist established a water stress index that indicates that humans require an estimated 100 liters/person/day for basic drinking bathing and cooking. 5-20 times this amount is needed to meet the demands of agriculture industry and energy. Countries with over 1700 cu. meters of renewable fresh water per person per year will experience intermittent or localized water shortages. Chronic and widespread water scarcity occurs under 1000 cu. meters. The figures refer to renewable fresh water. Figures do not account for nonrenewable groundwater timing or seasonality or adaptability of nations. Amounts above 1700 cu. meters do not assure an abundant freshwater supply at all times and in all places.

Engelman R

Papers

Sustaining water easing scarcity: a second update.