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Adaptive Control of Capillary Water Flow Under Modified Subsurface Irrigation Based on a SPAC Model

M. Ohaba, M. B. Zainal Abidin, Q. Li, S. Shibusawa, M. Kodaira, K. Osato

Tokyo Unviversity of Agriculture and Technology

Soil moisture in a rhizosphere of a tomato is controlled adaptively based on a simple soil-plant-atmosphere continuum (SPAC) model. The water flow from a soil through a plant to the atmosphere is governed by the analogous rule of the SPAC model. In our experiment, we assume that plant transpiration is only affected by the water-potential of air when the soil moisture maintains at a constant value under the modified subsurface capillary irrigation. Thus, we try to use the water-potential of air as a linear control variable for the adaptive control of the water flow into the rhizosphere. The experimental setup is composed of a soil-plant system, a subsurface capillary irrigation system and a water level controller in a reservoir. A circular fibrous medium is situated on the pot bottom, which can supply water through a string from a reservoir as much as plants need. The water volume rate in both the transpiration and the water flow into the rhizosphere is determined from the mass changes in the soil-plant system and the reservoir. During the course of our experiment, the plant growth responses such as height, number of branches and tomato fruits etc, are measured every three days. The experimental results such as plant growth responses and water saving are discussed. Further, the effects of the adaptive irrigation control based on the SPAC model are evaluated in order to increase in water use efficiency.

Keyword: capillary irrigation, soil moisture, adaptive control, SPAC model, water saving

M. Ohaba M. B. zainal abidin Q. Li S. Shibusawa M. Kodaira K. Osato Engineering Technologies and Advances Poster 2012

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