Summary of the Current Research and Implications for the Future

Abstract

As the conclusive section, this chapter starts to review the transition of rice production in tropical Asian countries during the 50 years, then examines the significance of factor analysis for soil evaluation performed by Kawaguchi and Kyuma (1977) in relation to the Green Revolution, and finally summarizes the findings from our research to make a conclusion and give the implications for the next-generation rice cultivation. Steady increase in rice production in tropical Asia was ascribable to the reclamation of new rice fields and the spread of double or triple cropping practices as the benefit from the Green Revolution technologies. The standardized multiple regression analysis using the factor scores of the IP, OM, and AP in Kawaguchi and Kyuma (1977) suggested that the increasing yield of high-yielding varieties in the 1960s at the initiation of the Green Revolution might depend largely on the soil nutrient pools because of insufficient fertilizer application. Our research could successfully grasp and clarify the influences of the Green Revolution on soil fertility status in Thailand, the Philippines, Malaysia, Bangladesh, and Indonesia as follows: (1) P status was remarkably improved in all the countries, (2) Regional trends of the IP and OM were persistent over the 50 years due to intrinsic soil characteristics, (3) Soil organic matter was increased in many cases, suggesting the potential of the paddy fields in tropical Asia to contribute to carbon sequestration, (4) The levels and composition of exchangeable bases depended on management practices as well as the differences in parent materials and physiographical environments, (5) Silicate could be replenished from irrigation water in addition to in situ mineral weathering process, (6) Total element contents and micronutrient status were varied between regions and changed during the long term, and (7) Soil texture and clay mineralogy were occasionally changed probably due to the inflow or outflow of soil particles by repeating irrigation. Facing global and regional environment issues as well as still-growing food demands, rice production in the post-Green Revolution era will require more careful and precise soil management systems. Of prime importance is to understand the diversity of lowland paddy soils in tropical Asia.