What Are You Looking For?
When reviewing the results of a water analysis it is important to note excess or minimal levels first, before studying the balance of parameters measured. Presented in Table 1 are some ornamental irrigation water quality guidelines. The characteristics in set one should definitely be monitored. They are the minimum set of analyses that should be done on a regular basis. Set two characteristics are desirable but not as essential.

Total Salts
If you have compared your water analysis to the guidelines in Table 1 and discovered an EC problem, you should take comfort that you are not alone. High salt content is a relatively common problem.

Salinity is the total quantity of salts dissolved in water, and one way to measure it is by electrical conductivity (EC). A commonly used unit for measuring conductivity is millimhos per centimeter (mmhos/cm) which is equal to the millisiemen (mS). More recently mmhos/cm has been renamed decisiemens per meter (dS/m). The two unit's values are equal; only the name was changed. Another commonly used unit of measurement for salinity is total dissolved salts (TDS), measured in parts per million (ppm).

The relationship between water's electrical conductivity (ECw) and its total dissolved salts (TDS) is:
ECw (in dS/m) X 640 = TDS (in ppm or mg/l)

Affects on Plant Growth
The total amount of dissolved salts in a water supply constitutes its salinity. The cells of plant roots absorb water as a result of the differences in osmotic pressure between the cell contents and the surrounding soil water. Whenever salinity of the soil solution is near to or greater than that of the cell contents, plants are unable to take up sufficient water for growth and other processes. Mature plants can tolerate higher salts than young plants. Some common salt sensitive ornamental plants are Cotoneaster horizontalis, Photinia fraseri, Ilex cornuta 'Burfordii,' Vinca minor, Hibiscus rosa-sinensis 'Brilliante,' Nanadina domestica, Azalea sp., Gardenia sp., and Limonium perezii, to name a few.

When evaluating salinity, it is important to note the dominant anion in the water. For water with bicarbonate as its principal anion, the salinity hazard is much lower than if the principal anion were chloride. The irrigation water constituents of greatest concern to growers of ornamental species are chloride, boron, and sodium. High sodium and bicarbonate are the two I have come across most often, to date. Sodium. Plant roots can absorb sodium and transport it to leaf tissue where it accumulates. Sodium toxicity symptoms are similar in appearance to those of chloride toxicity; i.e. marginal scorch on older leaves. Bicarbonate. The principle concern with bicarbonate is not that it is a toxic ion, but that it increases soil pH. Waters that contain sodium and bicarbonate as the major cation and anion can cause serious problems for plants.

Managing Salinity
When high salt levels exist, there are various options for managing the problem: 1) dilute with collected rainwater or other low salinity water sources; 2) use reverse osmosis water treatment, if the problem is severe enough to warrant or if using for misting cuttings, irrigating seedlings and/or salt sensitive crops; 3) do not allow the root medium to dry excessively to avoid concentrating the salts; and most generally, 4) leach with low salinity water to remove accumulated salts. In Table 1, waters with electrical conductivity values above 0.75 dS/m will present increasing salinity problems. To control salinity, enough water must be applied to produce a leaching fraction of 10 to 25 percent. The leaching fraction is the percentage of applied water that must leave the root zone or container to accomplish the degree of leaching desired. The leaching fraction may be calculated by using Formula 1.

Formula 1:

Volume leached
----------------- X 100 = Leaching fraction
Volume applied

Another common sense management suggestion is that since fertilizers add additional salts it is usually desirable to start with water sources that have as low a salinity level as possible. When high salt levels are experienced, the water should be analyzed and those specific elements making up the salts should be avoided or at least reduced in the fertilizer program.

Summary
Because we do have water quality issues affecting production, every greenhouse and nursery fertilizer program in Oregon should start with a complete water quality analysis. Any grower who wants to manage water quality effectively should invest in two pieces of equipment:

1. a pH meter – to monitor changes in soil pH, and
2. an electrical conductivity (EC) meter – to measure salinity of irrigation water and soil solution extract periodically through the life of the crop. Additional analyses should be made periodically by a competent laboratory in order to monitor other potential problem areas.