A simple new estimation method for water status in satsuma mandarin (Citrus unshiu Marcow.) was developed, expecting to improve irrigation in the summer and early autumn seasons and increase fruit quality. As a patch test, a "Water Stress Indicator" stuck on the abaxial side of the leaf changed color depends on the water status of the satsuma mandarin tree. The indicator is based on the fact that Cobalt(II) chloride changes its color by hydration reaction; if there is sufficient moisture, the light blue turns to a light red. To determine the appropriate condition of this indicator usage, the relationship between the diurnal change of transpiration and the leaf water potential (LWP) before sunrise was investigated. There was a clear difference in the transpiration rate of satsuma mandarin leaves around midday on a comparison of satsuma mandarin trees under various water statuses. If the transpiration rate was above the cut off (3 µg・cm −2 ・s −1 ), LWP should be −0.8 MPa or more. Together with these results, the indicator should be stuck on the abaxial side of a leaf that receives sufficient sunshine around noon. Under this condition, if the indicator color turns light red within 5 min, the satsuma mandarin tree tested is not under water stress. The "Water Stress Indicator" would facilitate visual estimation of the water state from summer to early autumn.
We evaluated the water status of peach, grape, Japanese pear, and satsuma mandarin trees using a 'water-stress indicator sheet'. This sheet indicates the water status of a sample by changing color (from blue to light pink); this is caused by a reaction between the sheet and water evaporating from the leaf onto which it is pressed. Decreases in the evaporation rates of grapes, peaches, and Japanese pear under water-stress conditions can be estimated using the time required for the indicator sheet to change color. This color change occurs in 100-110 s when in contact with the leaves of non-water-stressed plants, but when the plant is under sufficient water stress to reduce the evaporation rate by half, the change in color takes 200 s. In satsuma mandarin, it takes 130 and 230 s, respectively. Thus, the time elapsing between initial contact and the change in sheet color can function as a measure of the water status. However, when taking measurements for practical use, it is necessary to maintain conditions such as solar irradiance at a constant level.
We examined the effects of summer fertilization and pruning on nitrogen levels in the bleeding sap and petioles of 'Muscat of Alexandria' grape vines under forcing culture from December. In the summer of 1999, 9 vines under soilless-culture were treated with combinations of 3 different fertilization levels with 3 pruning procedures. The effects of the summer fertilization and pruning on inorganic nitrogen levels in the bleeding sap were not clear. The summer fertilization affected the nitrate nitrogen levels in the petioles at the berry set stage in the subsequent season, since the levels of nitrate nitrogen in 10 gN・m −2 (10 g nitrogen application・m −2 ) and 15 gN・m −2 were higher than that in 5 gN・m −2 in the previous summer. The effect of summer fertilization on the inorganic nitrogen level was marked in the berry set stage; however, the difference in nitrogen levels among the fertilization treatments became indistinct at veraison. The summer pruning also affected the nitrogen levels in the petioles, since the levels of nitrogen in the vines pruned the previous summer were higher than the levels in those that did not undergo summer pruning. However, the severity of winter pruning did not affect the nitrogen levels in the petioles at any of the sampling times.
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