Salinity, or excess salt in the soil profile, is often called the "silent killer", because of the devastating effect salinity can have on irrigated agriculture. With increasing agricultural irrigation efficiency, there is a risk of salt build-up in the soil that can significantly reduce crop production. 

What level of soil salinity is critical?

Salinity is the concentration of salts in soil or water; when it exceeds a certain level it affects plant growth.  Highly efficient irrigation practices can reduce drainage, associated with salt build up in the root zone. A salinity level of >2 dS/m affects the growth and productivity of wine grapes. Above graph from Australian trials found grape grape production reduction from salinity levels of 2 dS/m and higher. At 6 dS/m, production is reduced by 50%.

If the salinity is too high, the only way to remove the salts is to flush out by rain or deep draining irrigation. Nitrogen fertilizer application can increase salinity and should be monitored closely, especially on sites with potential salinity concerns.

Some crops have a higher tolerance for soil salinity. For example the ECe threshold for wheat is 6.0, for cotton 7.7, and for barley 8.0 dS/m.