Water quality is defined in terms of the elemental composition and concentration of salts dissolved in the irrigation water. The ratio of precipitation to potential evaporate-transpiration varies seasonally in arid and semi-arid climates. Salinity is a common problem in poorly managed container nurseries when fertilizer salts are allowed to build up in the medium without adequate leaching, but is not usually a problem in bare-root nurseries. Salts injure bare rootstocks in the following ways.
- by increasing the osmotic pressure of the soil solution, causing stress and drought
- by decreasing soil permeability owing to lose, soil structure and aggregation caused by the deflocculation of soil colloids (particularly in clays)
- by direction toxicity from sodium, chloride, borate, other ions and
- by the change in nutrient availability owing to changes in pH
Osmotic stress
The following values are often used to access the effects of salts on growth
Salt hazard | Conductivity (micro mhos/cm) |
Low | < 250 |
Medium | 250-750 |
High | 751-2250 |
Very high | >2250 |