I hope someone here knows a bit about soil and water analysis.
In March 2013, I had the soil tested in my yard. I had an area about 15 feet wide that
was had such bad soil NOTHING would grow - not even a weed.
In 2003, we had 22 inches of rain (average here is 12 inches). The area was very boggy.
We dug it up thinking it was a broken water pipe. It wasn't. Ground water is 6 feet below
the ground. Salt deposits were all over the grass (well dead grass because of salt)
While the "pit of despair" was open, I sent in a sample of soil.
The report came back with a letter.
The letter says "The soil is PH neutral with high fertility except for modest nitrogen.
However it is not suitable for sustaining the growth of most plants, especially crops.
The salinity is excessively high at 8.45 millimho/cm. Normally the salinity should be
less than about 3 for many plant and lower for salt-sensive plants. Soluble sodium,
chloride and calcium are high. Lead is low. Cobalt is moderate"
Ironically we had 2 inches of rain last year. I'm considering uncovering the pit again and
using the water for the hill behind it (80x60 feet) for my food forest. I'm wondering if I
used half of this water and have of the city water how my nitrogen fixing and fruittrees would be. (I'd cut it with rainwater if I had any!)
Soil salinity is not something I'm likely to come across in NZ. Whew!
In this fao document they say 4.5-9 millimhos/cm is 'slightly saline', but I think even 'slightly' is too much for many plants.
I think this is an important conversation, and hopefully drylanders will comment
More drought combined with more saline groundwater is going to be a reality for more and more people.
Even slightly salty, for irrigation water can be too much. As the water evaporates, salt is left behind. The soil becomes more saline with each watering. It can only work in spots that occasionally get massive amounts of good quality water, which is used to flush the salt from the soil. This type of surplus is not usually the case, in areas with salt problems.
It's better to harvest rain water and gather other surface water.
If using saline water to irrigate non-saline areas is imprudent -- as I understand it to be -- how about this? Try to find a salt-tolerant species that produces.copious foilage, then use that foilage as a green mulch for the areas you want to irrigate. This will contribute a quantum of moisture, but also reduce evaporation and make the irrigation water (from rain or whatever) go further. (This assumes there are salt-tolerant plants that make non-saline foilage, which I believe but have not researched.)
In other words, leave your salty groundwater where it is, but try to make it a resource.