over the last three decades, which helped Bangladesh avoid a looming hunger crisis, despite high population growth and dwindling amount of arable land (Hossain et al., 2006). The rice-breeding programs at IRRI and its partners in Asian countries  demonstrated how AKST requires  continuous development of new cultivars to secure the world's food supply.

The rice—wheat system of the Indo-Gangetic Plains. Rice-wheat cropping has been practiced for a thousand years, but it expanded rapidly, particularly in northwest India and Pak­istan, only since the mid-1960s, following the Green Revo­lution. The rice-wheat belt occupied nearly 24 to 27 million ha in South Asia and East Asia. Rice was mostly grown in flooded fields, while the ensuing wheat crop required well-drained soil (Ladha et al., 2004). The system occupied 13.5 million ha in the Indo-Gangetic Plain of South Asia in 2001 (Timsina and Connor, 2001). Rice-wheat systems evolved with the introduction of wheat into traditional rice areas in Bangladesh, eastern India and Nepal and rice into tra­ditional wheat areas in northwest India. The driving force for expansion was the need to intensify cropping to meet an increasing demand for food. It was made possible by the de­velopment of short-duration and medium-duration rice and wheat cultivars. Their combined productivity responded to improved nutrient management, pest control and the expan­sion and improvement of irrigation. The rice-wheat system is complex. Overall optimum management strategies must be established for the alternating and contrasting anaerobic environment required for rice and aerobic environment for wheat. A summary of the sequence of the technology and its effect on productivity is as follows:
•   Before the Green Revolution, yield was small and the system operated with few inputs and much human and animal labor.
•   As short-season rice and wheat cultivars became avail­able, management focused on expanded irrigation and improved management. During this early expansion there were no environmental issues to counteract the benefits from increasing productivity. Yields increased with further intensification.
•   Further intensification included new cultivars, nutrition and mechanization. Early sowing of wheat to avoid heat stress and low yield during flowering and grain filling was a major strategy for yield improvement.
•   Subsequently, yield increase slowed and yield declined in some places from a combination of causes. Evidence showed deteriorated soil structure and fertility from excessive cultivation and nutrient extraction from the more intensive system, operating with ever-increasing yields. Problems arose from irrigation with both exces­sive extraction of groundwater and accumulating salts in regions with low water quality. Decreased solar ra­diation and increased minimum temperature also con­tributed to yield decline (Pathak et al., 2003).
•   The recent phase was to recuperate yield. Attention to water and labor use and environmental problems led to much new technology across the entire Indo-Gangetic Plain. New techniques and machines for planting ena­bled more rapid and timely crop establishment. Reduced cultivation and site-specific fertilizer management were

reversing soil deterioration. Bed planting was intro­duced in some places to improve water management and diversify crops away from a strict rice-wheat sys­tem. Fertilizer requirements were more precisely de­fined, and soil and tissue testing enabled more effective and efficient nutrient management. Laser leveling of land, aided by more accurate water requirements, im­proved irrigation efficiency. Less stubble burning con­tributed to improved air quality and more soil organic matter. These resource-conserving technologies were to improve farmer income by increasing input efficiency, maintaining crop productivity and enhancing crop di­versification (Gupta et al., 2002; Ladha et al., 2003).

Rainfed wheat production in the State of Victoria, Austra­lia. The Australian wheat industry, exemplified by the State of Victoria, had already passed through two phases of de­velopment when the rapid development of a lucrative world market for wool following World War II provided an op­portunity for significant change (Connor, 2004). It became economical to improve pasture by species composition and fertility. "Sub and super," subterranean clover (Trifolium subterraneum L.) and superphosphate fertilizer, became the buzzwords for pasture development. Sheep-carrying capaci­ty of pasture increased markedly and encouraged close inte­gration with wheat production. Pastures were managed for sheep and to build up nitrogen to extract during a cropping phase. Other technology supported the greater economic benefits that flowed to farmers from increased wheat and sheep production. Plant breeding continued, horses were replaced by tractors, and new machines were developed for tilling and harvesting. Herbicides and pesticides became available, and increasingly precise fertilization for pasture legumes, including micronutrients manganese (Mn) and mo­lybdenum (Mo), became possible. Fallowing became less fre­quent. Wheat yields had risen to around 2 tonnes ha-1 by the 1980s. The system was mostly seen as ecologically stable.
     With the application of inorganic nutrients, leguminous pastures with increased nitrogen supported profitable sheep and wheat production. The system did not, however, persist into the 1990s because the wool market collapsed. Further­more, soil acidification and salination were unanticipated environmental effects of the system. Clover growth and ni­trogen fixation were reduced, and consequently the overall productivity of pastures and wheat crops declined. The solu­tion lay in liming and changing the water balance to keep the salt at the depth where it had accumulated under native vegetation. As a result, a more diverse system was sought, one that involved less pasture, less fallow, perennials such as lucerne and trees in agroforestry systems, and a wider range of crops including canola, lupine, field pea, fababean, chickpea and lentil. There was also increased use of zero tillage, controlled traffic, yield mapping and precision farm­ing. Nitrogen fertilizer entered the system. Plant breeding continues, now for a wider range of species and by apply­ing new biotechnology techniques such as marker-assisted breeding. But so far genetically modified crops (GMO) have been avoided. Although there has been some local opposi­tion to GMOs, the dominant concern has been to maintain access to overseas markets.