Irrigation water amounts must coincide the growing stage of your crop. Apply the minimum needed to flush salts from soil. This means that you always have to give a little more water than the crop consumption, to allow leaching of salts below the root zone. Heavier soils require larger water applications than lighter soils, in order to avoid salinity buildup.
The leaching requirement is expressed as:
LR = Water leached / Water applied
A general equation to calculate the leaching requirement is
LR (%) =ECiw/(5ECth-ECiw)
Where ECiw is the EC of the irrigation water, and ECth is the threshold salinity measured in the saturated soil extract, above which yield begins do decline (both in ds/m).
The total amount of water to be applied is AW = ET/(1-LR)
Where AW is the amount of water to be applied and ET is the water consumption based on evapotranspiration.
Irrigation regimen and intervals must be appropriate to the soil conditions and to growth stage of the crop. Frequent and shallow (superficial) applications result in salt accumulation in the root zone, while larger applications, in longer intervals, will flush the salts below the root zone.
The fertilizers type and their quantities should coincide with to the requirements of the crop and with nutrients which are already in the soil. There are fertilizers which contain salts which are not taken up by plants in large amounts, such as chlorides. These salts tend to accumulate in the soil.
Soil analysis gives you a better indication of the salt content in the soil, without which you'll be only guessing. Guessing often comes close enough, but in many cases growers realize there's a salinity problem only after yields are decreased or crop quality is reduced.
A practical approach in order to prevent salinity buildup early enough is sampling the soil 5 times over a growing period of 8 months (a test every 6 weeks or so). It is recommended to do at least one water analysis as well. The tests will indicate any change in soil content, allowing you to adjust the fertilization and irrigation regimen as needed.
This is the cheapest, most practical way to follow up on salinity status, keeping your crop quality and yield at optimal level.
When you identify a salinity problem during the growing season, it is recommended to flush the field, even if it means risking some crop damage, rather than allowing further deterioration of the crop due to salinity.
Flushing applications should be carefully planned according to the crop conditions and growth stage. In light soils, which drain easily, the impact of flushing on the crop is usually insignificant.
In heavy soils, water infiltration and drainage problems may be encountered, resulting in excess of water and lack of air to the roots. Flushing heavy soils is a prolonged process and its final result is difficult to anticipate in advance.
Therefore, extra care should be taken when growing on heavy soils, as to not reach salinity buildup at all, or at least identify the problem early enough, when salts levels are still relatively easy to flush.
If all else fails and flushing is the chosen course of action, in heavier soils, not more than the maximal water amount that can be absorbed by the soil should be applied, and the longest intervals possible should be maintained. In the meantime, fertilization should be based only on Nitrogen and only the minimum amount should be applied.
The water used for flushing should be the highest quality possible, because the purpose of the flushing process is to decrease the soil salinity to the levels of the irrigation water.