Cabbage evapotranspiration rates were greater under DI and SDI in the early and later stages of growth, respectively (Fig. 1). LAI of cabbage was also greater under DI and SDI in the early and later stages of growth, respectively.
The roots penetrated to slightly below 15 cm depth in the early stage of growth 17 days after transplanting (DAT). This means that under SDI, only parts of the roots are likely to reach the water-supplied area. This was one reason why the evapotranspiration rate of cabbage under SDI was lower than that under DI in the early stages of growth before 20 DAT. The root TTC reduction capacity (root activity) of cabbage under SDI increased when its evapotranspiration rate increased in the later stage of growth (Figs. 1 and 2). These results demonstrate that the root activity and evapotranspiration rate of the plant under SDI increased in the later stages of growth, although the evapotranspiration rate was lower and the growth was slower in the early stages of growth than for plants under DI. A nutrient-rich and water-rich environment would be preferable for plants under DI and SDI in the early and later stages of growth, respectively. Thus, plant growth under DI and SDI appears to change according to whether other environmental factors such as temperature and solar radiation are advantageous in the early or later stages of growth. These factors are what created the uncertainness in the difference in shoot dry weight and yield between DI and SDI.
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