Fertilisers increase the salt concentration of the soil solution or the salinity index of the fertiliser. The salinity index is the ratio of the osmotic pressure from the addition of some fertilisers to the osmotic pressure developed by applying the same amount of NaNO3. In general, fertilisers with a higher nutrient content have a lower salinity index. Nitrogen and potash fertilisers have a higher salinity index and are more detrimental to germination than phosphate fertilisers.