Rainwater harvesting to retain water has been seen in some semiarid areas in ESAP. Rainwater harvesting has shown considerable potential in semiarid areas because it could supply limited irrigation at the key stages of crop growth by using stored rainwater. A number of cases in China and India have shown significant increase in crop productivity through rainwater harvesting. In Gansu Province in China, for example, yields of maize and wheat on the experimental sites increased over 50% (Liu et al., 2005).
Rainwater harvesting technology is simple for local people to install and operate. It is convenient because it provides water at the point of consumption and family members have full control of their own systems, reducing operating and maintenance problems. The disadvantage is the limited supply and uncertainty of rainfall. In addition, numerous small-scale water-harvesting and storage systems in a basin could have similar effects on river flows and aquatic ecosystems as a large dam and canal irrigation. For example, along the Yellow River, bunds and plugging gullies were effective in encouraging agriculture and in reducing erosion, but evidence showed these practices reduced river discharge (Zhuetal., 2003).
Improved land management techniques and agricultural production systems have received growing attention for improving water productivity of rainfed systems. Such technology has been referred to as "green [soil] water management." In some areas, minimum or zero tillage proved effective in improving soil moisture and crop yields in rainfed land (Hatibu and Rockström, 2005). Mulching, terracing, contouring and microbasins are also important in maximizing rainfall infiltration into the soil to increase yields. No-till and conservation agriculture maintains and improves crop yields and resilience against drought and other hazards, while protecting and stimulating the soil. The essential features of conservation agriculture are minimal soil disturbance and maintenance of a permanent cover of live or dead vegetative material. The cover protects the soil against erosion and water loss from runoff or evaporation. A major impediment to successfully introducing conservation agriculture is that management skills are complex. In many ESAP countries, any production system that includes crop rotation is complex because it calls for coherent management over more than one or two crop seasons. Farmers who have adopted these systems need to understand them and the reasons for the various procedures to be able to adapt them to their needs and conditions to balance crop rotation with market requirements (Box 2-1).
Recently, increasing emphasis has been on integrated rainwater and irrigation water management. Because obtaining additional water for irrigation is difficult and water in rainfed systems is unreliable, agricultural water management has shifted from pure rainfed or fully irrigated systems to emphasizing intricately connected soil conservation and supplemental, drip, ground and surface irrigation.
2.2.2 Development and application of modern technology and inputs
2.2.2.1 High-yielding varieties—the Green Revolution
The historical focus by international and national research institutes has been food crop production technology, em- |
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Box 2-1. Potential of rainfed agriculture.
There are different views on the potential of rainfed systems. Evidence exists for great potential for poverty reduction from new approaches to enhancing rainfed agricultural systems. New pro-poor small-scale, low-cost approaches such as treadle pumps, water bags and water harvesting are key to unlocking rainfed potential and reducing poverty on marginal rainfed lands. Although crop yields seem low considering the amounts of land, water, labor and capita required, new technologies are available to help farmers predict uncertain variables such as rainfall. This improved predictability can help increase the contribution of rainfed agriculture.
Others state that although rainfed agriculture has been the focus of research for many years, gains are not forthcoming. Dependence on approaches to enhancing rainfed agriculture involves high risk due to climate variability, particularly affecting small scale and poor farmers. As poor people often live in semiarid agricultural environments where the ability to cope with weather variation is very low, the failure of crop often means starvation or even death. A study in three semiarid watersheds in India showed that large scale investments in soil and water conservation did not have a significant impact on dryland yields, at least not under prolonged conditions of drought (Bouma and Scott, 2006). phasizing improved yield varieties—the Green Revolution. Modern plant breeding and improved agronomy, including the use of inorganic fertilizer and pesticides, have been components of the strategy to increase production (Friedman, 1990). Nearly three-quarters, 71%, of production growth since 1961 has been from yield increases. Increased yields have contributed to greater food security within developing regions and contributed to declining real prices for food grains.
In the 1960s, when the International Rice Research Institute (IRRI) was formed, breeders found the main constraint to rice yield was the architecture of traditional tropical rice cultivars (Khush et al., 2001). Although tall cultivars responded positively to nitrogen fertilizers, competed well with weeds, and provided much straw for fodder, fuel and construction, they lodged and lost yield. The Japanese had realized the value of short-straw cultivars in the quest for high yield and introduced the trait into rice around 1900. By the 1950s, semidwarf rice could be found among the landraces in many Asian countries, including in subtropical China. Taichung Native 1 (TN1), a semidwarf cultivar from Taiwan (China), was first planted in the tropics in the late 1950s, but it was highly susceptible to major diseases and insects in the tropics (Peng and Khush, 2003). In 1962, IRRI introduced dwarfness into tropical rice by crossing the dwarf Taiwanese cultivar Dee-geo-woo-gen into the tall Indonesian cultivar Peta. The result was IR8 (the 8th cross), the first lodging-resistant and fertilizer-responsive cultivar. Farmers rapidly adopted it and it became the symbol of the Green Revolution in Asia. After the release of IR8, |