Frank Thompson said:

what can I do to make soil fertile again if ihas been soaked in enough
brine to kill vegetation

Apply plenty of salt-free water.

From Colorado State extension service:

Saline soils cannot be reclaimed by any chemical amendment, conditioner or
fertilizer. Only leaching can remove salts from the plant root zone. The amount of
water necessary is related to the initial salt level in the soil, the final salt level
desired and the quality of the irrigation water.

Six acre-inches per acre of good quality leaching water passing through a foot of soil
will reduce the salinity by about 50 percent. One acre-foot per acre will reduce the
salinity by about 80 percent, and 2 acre-feet per acre passing through 1 foot of soil
will reduce the salinity by about 90 percent.

For example, if the soil has an average salt level of 18 dS/m in the top foot and the
salt level is to be reduced to 2 dS/m, the amount of leaching water needed is
calculated in the following way:

Amount to be reduced, 18 - 2 = 16
Reduction desired, 16 / 18 = 89 percent
Leaching water needed, 2 acre-feet/acre

--
Pat in Plymouth MI

Any technology distinguishable from magic is insufficiently advanced.
(attributed to Don Marti)