ABSTRACT
The seeds for a wetland rice agroecosystem in South and Southeast Asia were sown nearly 5 to 6 millennia ago. Since then, it has consistently spread across this vast agricultural zone. Today, this intensive rice ecosystem occupies nearly 10% of global agricultural soils, and dominates the humid and sub-humid tropics of the Indian sub-continent, Indo-china area, China and Far East. Within Southeast Asia, the rice belt occupies 60 to 70% of cultivable land, and approximately 60% of the human population of this zone thrives on rice as the staple cereal and the main source of carbohydrate. Rice, actually outcompetes other dietary sources in this zone, through its most acceptable palatability and nourishing features. The rice dependent population in this agrobelt is suspected to increase by 7.2% annually, over the previous levels. Hence, demographists forecast that one billion more rice eating population will be added by 2025 (Lampe, 1993; IRRI, 1995; Tribe, 1995, FAOSTAT, 1999). Projections for area expansion of this already vast agroecosystem are bleak. Hence, consensus among rice experts has been to intensify and raise productivity per unit area. During the second half of 20th century A.D., the development and adoption of high yielding, semi-dwarf rice genotypes, and high nutrient inputs through chemical fertilizers have already intensified this irrigated rice ecosystem, causing enormous changes in the nutrient dynamics. Presently, it consumes 3 to 4 million tonnes of N, P, and K, which is equivalent to 80% of total fertilizer based nutrient inputs in Southeast Asia (Table 4.1). Limits to such intensification are not yet discernible. Trends and opinions among present rice specialists point towards further intensification, through increase in rice grain yield per unit area. For this to happen, Lampe (1995) states that significant changes in plant architecture, and genetic make-up is necessary. The super varieties and hybrids being generated may hold promise through their potential to yield over 12 to 15 t grain ha-1 (Yuan, 1992; Amano et a l 1993; Kush, 1996; Fisher, 1998).
