Evaluation of the applicability of the water-saving vegetable cultivation technology by the soil moisture simulation

A water-saving cultivation technology for tomatoes has been developed in Nong Saeng village, Khon Kaen Province, Northeast Thailand. The technology utilizes the water stored in the soil during the rainy season. By using this technology, it is possible to reduce the amount of irrigation water used to less than 5 mm per crop cycle. In this area, the standard irrigation level is more than 500 mm. Since this technology is considered to depend on soil moisture, we demonstrated the mechanisms involved by using a soil moisture simulation. Further, we evaluated the applicability of the technology to other soil types in Northeast Thailand. In brief, the method we used was as follows. In the first step, we simulated the actual soil moisture dynamics from the end of the rainy season to the period of transplanting. In the next step, we carried out identical simulations for four soil types typical to Northeast Thailand. On the basis of the results obtained, we evaluated the applicability of the water-saving technology by comparing the water supply capacity of each soil type. For the analysis, we used the HYDRUS-1D simulation code, which has often been used in the agricultural field. The initial soil condition at the end of the rainy season (September 23, 2004) was designated as the saturated condition. The parameter for the dry sand layer effect was adjusted so that can be equal to the soil moisture condition of the transplanting time (December 1, 2004). The actual evaporation observed during this period was 150 mm. It was enough big dry sand layer effect to the 420 mm of the potential evaporation. Further, using these parameters, we simulated the soil conditions present from the time of transplanting to the time of harvesting. The results obtained were similar to the soil moisture dynamics that we had measured. Lastly, we simulated the soil moisture dynamics in the four soil types that are typical to Northeast Thailand (Nam Phong, Ubon, Roi-Et, Phimai). We compared the water supply capacities of these soil types. We observed that the technology was more suitable for Roi-Et and Phimai than for Nam Phong, where it was developed. The suitability of Ubon for the usage of this technology was lower than that of Nam Phong; however, the difference between the two was small. These results demonstrate that this water-saving technology can be applied to a large area of Northeast Thailand.