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Plants, like all living things, need nitrogen to build amino acids and other essential biomolecules. Although nitrogen is the most abundant element in air, the molecular form of nitrogen found there is largely unreactive. To become useful to plants, that nitrogen must first be "fixed," or busted out of its molecular form and linked with hydrogen to make ammonia. The plants can then get at it by catalyzing reactions with ammonia.
But plants can't fix nitrogen. Bacteria can.
Some legumes and a few other plants have a symbiotic relationship with certain bacterial species. The plants build specialized structures on their roots called nodules to house and feed the bacteria, which in turn fix nitrogen for the plants and assure them a steady supply of ammonia. Only 10 families of plants have the ability to do this, and even within these families, most genera opt out. Ever since the symbiosis was discovered in 1888, plant geneticists have wondered: why? If you could ensure a steady supply of nitrogen for use, why wouldn't you?
A global consortium of geneticists sequenced and compared the genomes of 37 plants—some symbiotic, some not; some that build nodules, some not; some agriculturally relevant, some not—to try to find out what was going on. The group's genetic analysis of the conundrum was reported in Science.
(Score: 3, Informative) by c0lo on Tuesday May 29 2018, @11:15AM
Same experience with a plot I bought at countryside. About 100 years ago, it used to be eucalyptus forest, then transformed in a grazing plot, but without too many amendments. The base rock is mainly quartz and in my case the pH is already at 6.5.
Without organic matter into the soil, the results will only go that much - see my case above.
And not all salts will be soluble - e.g. hydrated calcium sulphate (gypsum) is very weakly soluble even if its presence will improve a bit the water penetration.
As the pH improves, I'd suggest to try some green manure [wikipedia.org] cultures for a year or two - e.g. lucerne tends to develop deep roots (20 inches is not that unusual) and those will remain as organics in the soil for longer.
This one [wikipedia.org] if you feel the need for some trees around
See what you can find here [uniteddiversity.coop] - this one is a classic [uniteddiversity.coop], this one [uniteddiversity.coop] as well even if a bit outdated (there are some more recent authors that went deeper). See other things to read in the same permaculture folder.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford