| Abstract | Rice production is the main livelihood in rural Vietnam in general and Ma River basin -Centre of Vietnam in particular. However, rice yield sin Ma River basin are lower than these in Red River delta and Cuu Long River delta. Moreover, poverty is serious issue in the countryside of Central Vietnam in general. This research combines modeling and optimization approaches to contribute to understand the factors that limit yields, productivities, and the actual technical efficiency of irrigated rice farming systems in Ma river basin. The Crop Water Productivity Model Aqua Crop was used as it can simulate the growing cycle and yield of rice crop. It integrates knowledge about soil, climate, crops and management. The simulation results of rice yield under different condition (actual condition, non-limiting soil fertilization, non-limiting irrigation water and non-limiting soil fertilization and water at the same time) reveal large gaps between potential and actual yields. Such gap is larger and caused by water shortage in the dry season cycle. It is less marked in the rainy season cycle. In both seasons, lack of soil fertilization is another significant cause for low yield gaps. The Residual Imputation Method (RIM) has been used to ascertain the marginal value (shadow price) of irrigation water. Results show that the average value of irrigation water is 0.170 USD/m3and 0.150 USD/m3for the dry season and rainy season, respectively. Results also reveal that there are some plot farms with low, nil, or even negative marginal values of irrigation water, owing to actual practice of non-remuneration of self, family labor, while RIM analysis usually involves monetization of all production factors at local market price. This highlights the very low income situation of many in these communities. The technical efficiency in rice cropping system was determined by Data Envelopment Analysis(DEA)approach. In term of rice production, the inputs are: machinery fee for land preparation(cost per ha), labor for field management (man.day per ha), fertilizer (mass per ha) and the only one output is rice yield(mass per ha). In term of total income from rice field, the inputs are: machinery for land preparation, labor for field management, fertilizer, machinery fee for harvesting, threshing, transportation and labor for drying(cost per ha); and the output is total income from rice sales (monetized in case of self consumption). The results show that high machinery fee and over-application of labor are the main causes of technical inefficiency. About60% of plot farms are inefficient with regards to rice production, and 40% of plot farm were inefficient with regards to total income from rice field. |