The productivity of Asia's cereal systems is of fundamental importance for its 3.8 billion people. Rice, maize, and wheat cover about 88% of the area under cereals and 95% of the cereal production. The total harvested area under these three crops is 259 Mio ha with an annual production of 936 Mio t and average yields of 3.72 t/ha (FAOSTAT 2005). Production share is 57% for rice, 24% for wheat, and 19% for maize. Wheat area and production have been declining since the mid 1990s while yield steadily increased to 2.9 t/ha at current. Rice and maize yields average 4.1 t/ha. Rice area is stagnating and yield growth slowed considerably since the 1990s so that production has been constant in recent years. Maize production has increased steadily in the last 20 years largely because of consistent yield growth. Annual yield growth was 4.2% for wheat, 3.3% for maize, and 2.0% for rice in 1961 to 2004. Yield increases can be attributed to improvements in germplasm, infrastructure, and management, and yield potential simulations indicate still significant yield gaps that can and will have to be exploited to provide the necessary future yield increases for a growing population. However, farmers will probably have to apply more site-specific knowledge to optimize yield, input use, and profit on their typically small landholdings in Asia. The necessary ecological intensification aims at satisfying the anticipated increase in food demand while meeting acceptable standards of environmental quality (Cassman 1999). There have been substantial improvements in the development and dissemination of balanced, more site-specific soil and nutrient management strategies for small scale faming in Asia in recent years. In this paper, we summarize key research on innovative strategies for improving productivity and nutrient use efficiency in rice, wheat, and maize. A common key objective is the application of technologies and principles to manage spatial and temporal variability associated with all aspects of agricultural production for the purpose of improving crop performance and environmental quality. Major focus is given to the evolution of individual technologies and their integration into consistent frameworks for decision support. Key elements of such frameworks include the use of yield potential models for yield gap analysis, target yields for the estimation of crop nutrient requirements, soil and plant based approaches for the estimation of indigenous nutrient supplies, target nutrient efficiencies for the estimation of nutrient needs, nutrient balances for the maintenance of soil nutrient supplies, real-time strategies for the effective management of nutrients prone to losses, relevant agronomic, economic, and environmental indicators for a comprehensive evaluation of practices and interventions (see Fig. 1), and participatory approaches for the on-site and evidence-based development, evaluation, and dissemination of improved management practices. Case studies from the region are used to portray adaptations to local needs, but emphasis is given to commonalities in approaches across crops and countries.
Figure 1. Framework for the evaluation of Site-Specific Nutrient Management (SSNM) in irrigated rice including performance indicators to assess the short- and long-term benefits of proper soil and nutrient management.