salts and sustainability

"the valuable ingredients of the soil ( potash, lime, magnesia, sulphuric and phosphoric acids is the list he gives in the preceding paragraph of the book...mostly alkaline) which are water soluable, have been washed out of the soil in humid regions, like our eastern states, by the rains of centuries. on the other hand, these elements have been accumulating in the arid soils of the west during those same centuries. they lie there like an inexhaustable bank account on which the plant life of the future may draw without fear of protest.
from " the conquest of the arid west." by william ellsworth smythe published in 1900. p.38
"in the west many soils are classified as saline or alkaline. irrigation water percolates through them, then returns to the river. it is diverted downstream, used again, and returned to the river. on rivers like the colorado or the platte the same water may be used eighteen times over. it also spends a good deal of its time in reservoirs which, in desert country, may lose eight or twelve feet off their surface to the sun every year. the process continues, salts are picked up, fresh water evaporates, salts are picked up, fresh water evaporates."
"cadillac desert" mark reisner p.459

those alkalines smythe is writing about make the desert bloom under irrgation...for a while...and it can be quite a while if there's good drainage...unless, of course, the water from the river you're using to irrigate already has a healthy dose of salts in it...or if there's poor drainage like the san joauquin valley which is gaining more salts in its soils every year...no drainage = waterlogged soils...evaporation=salts left behind...dump on more salty water and the problem just compounds...the fertile crescent grew lots of wheat 5500 yaers ago...by 4500 years ago they grew mostly barley...why? wheat is notoriously intolerant of salt...it kills wheat...barley can take mare salt in the soil...the alkaline soils of iraq have a clay underlayer that makes for poor drainage...salts accumulate until, eventually, nothing will grow...irrigation is a tricky business and the acerage in the desert southwest is as saline or alkaine as any in the world...by about 3700 years ago there were massive crop failures in sumeria because of the salt build-up..a process that took 1800 years or so...the san joauquin valley is losing an alarming ammount of acerage to salinity in just over one hundred..that "inexhaustable bank account" is more like a loan and the balloon payments are coming due.