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Changes in the evapotranspiration (ETP) of stock (Matthiola incana R. Br.) cv. White Dorse seedlings in a cell flat were measured, and regression analyses were conducted to investigate the relationships between ETP and environmental factors (solar radiation ; SR, saturation deficit ; SD and air temperature ; AT). In each sowing month, ETP was positively correlated with SR, SD and AT. Coefficients of determination (R2) were higher than 0.81 in SR throughout the year and larger than those in SD or AT in most sowing months. Seasonal variation of R2 in the regression lines was also lowest between ETP and SR compared to the other two factors. Thus, ETP was strongly affected by SR in each sowing month. When the yearly data were pooled, the regression line between ETP (y;mg·plant-1) and SR (x;MJ·M-2) was expressed as follows ; y = 276.2x+24.1 (R2= 0.873). Although R2 of a multiple regression equation became 0.921 when SD and AT were included as explanatory variables, there was little difference between the values of R-2-. A simple regression line of ETP and SR could estimate ETP. Change in ETP during seedling growth caused by the increase in the total leaf area was only 1.7 fold in comparison to changes in total dry weight and leaf area which were 10 and 7 fold, respectively. ETP at night was considered negligible in the estimation of ETP. When the transplants of stock are grown with an automatic fertigation system for a cell flat (12ml cell volume), supplying every 5 to 6 MJ·m-2 cumulative solar radiation may be a suitable value for fertigation frequency.

We demonstrated the practical utility of solar radiation mediated fertigation control for transplant production in a cell flat with an automatic ebb-and-flow fertigation system. Furthermore, we investigated seasonal changes in growth and productivity of stock (Matthiola incana R. Br.) cv. White Dorse as affected by fertigation frequency controlled in response to solar radiation (5 or 10 MJ · m-2) and scheduled time course (once or twice per day).The shoot dry weight of transplants and fresh weight of cut flowers were higher in plants fertigated with every 5 MJ · m-2 of solar radiation, sown between late April and late July. In plants sown during other periods, there was no significant difference in growtn and productivity among plants fertigated differently. When the plants sown in June were fertigated twice per day, the exposure was 5 MJ · m-2 in average of cumulatlve solar radiation from fertigation to subseauent fertigation. However, the maximum cumulative value exceeded 8 MJ · m-2. Water stress caused by the high solar radiation accompanied by high temperature and large saturation deficit may have resulted in reduced growth of the transplants and decreased quality of the cut flowers.When the stock transplants were grown in a cell flat (220 cells of 12ml cell volume), suffcient but not excess fertigation could be obtained by supplying nutrient solution every 5 MJ · m-2 of solar radiation with an automatic ebb-and-flow fertigation system.