Chloride in Recirculating Systems
A problem commonly associated with excess chloride is the inhibition of nitrogen uptake, resulting in chlorosis (Bernal et. Al, 1974). In this study there was no apparent inhibition of nitrogen uptake by chloride. A study by Falcon et al (1986) showed that damage by chloride may be caused at concentrations as low as 46 mgl-1in the irrigation solution. Yaron et al. (1969), found that foliar concentrations below 1% are not detrimental. Even though nutrient concentrations in this experiment (2.1) were as high as 1600 mgl-1, far in excess of 46 mgl1-, foliar levels were still below 1% (0.6477% in the 1600mgl-1 treatment). The difference between uptake in solution culture and soil culture is not well established and this study suggested that there was a significant difference between the two based on other published information.
In a typical commercial situation, the chloride levels would not reach the extreme concentration seen in this study unless there was a malfunction in the injector pump. Under such circumstances the total EC would rise due to an increase in all salts not simply chloride salts. This may have other detrimental effects such as acute root burn and consequent leaf loss. Although roses may not be classified as halophytes which use salt accumulation or salt regulation, they do seem to be able to store excess chloride in a similar manner as plants using salt regulation.
Although there were no detrimental effects of chloride from a potassium chloride source it cannot be assumed that another source of chloride will have the same outcome. Perhaps the high potassium is buffering the plant against chloride damage and other ions such as sodium or calcium may actually exacerbate the chloride effects. Lagerwerff and Eagle (1961) showed that high concentrations of potassium chloride increased plant growth and caused the osmotic potential of the leaves to fall by more than 300KPa.
Data suggest that high chloride levels alone in a solution system will pose little threat to roses. If the chloride is accompanied by sodium, such as from road salt drainage into ponds, potential problems exist. The damage caused by high salt levels is cumulative over successive crop cycles. Sodium was stored in stems to a much greater extent than in leaves. The next step was to determine if sodium would have similar effects when it was not combined with chloride.