This presentation will concentrate on the original methodology of the cropping systems research started in 1984. The research aims at improving the limiting factors of traditional ricecropping systems of Sathing Phra agrarian systems. This research is the second stage of a 1982-1983 study of Sathing Phra agrarian system which was a preliminary diagnosis necessary to define priorites of research and targets to improve the different farming systems of Sathing Phra. The results from this first stage demonstrated the limiting factors and characteristics of rice cropping systems according to their agro-eological localities and farming system types. Poor physical structure and low chemical fertilily of the soil and weed control problems that need to be improved. Fundamentals of cropping system analysis and their use to study technical improvements are discussed. A necessary double –level analysis of this methodogy includes (i) a systemic analysis to follow the effects of technical improvements on the system efficiency and reproducibility and (ii) and analysis of the interactions between the different elements of a cropping system in order to define the optimum conditions for employment of technical improvements in technical routes that fit the agro-ecosystem characteristics and farming system types. A program of research based on those two levels of analysis is then presented. In this research program we assume that the cultivation of legume crops grown with suitable technical routes, during the variable fallow durations between rice crops, may help improve soil physical and chemical conditions as well as weed control strategies of Sathing Phra rice cropping systems.