I have a pH neutral soil in Denver CO. All the sites I looked at seemed agreed that hard rock phosphate was a waste of time in this sort of soil, but they disagreed on soft rock phosphate. Also, if I add a lot of organic matter, wouldn't the acids produced by bacteria and plant roots release phosphates right in the root zone, despite the pH surrounding soil?
So, would it be a good idea, or a waste of time, to apply soft rock phosphate?
It's not "the acids produced by bacteria and plant roots" that does the heavy lifting in mobilizing the phosphorus in the soil but the soil fungi. There have been many studies done that show that mycorrhizal fungi are very efficient at finding phosphorus and translocating it to plants that need it. So what happens when you add lots of organic matter to the soil is that you add phosphorus (in the organic matter) and fungal spores and the whole soil food web starts to ratchet up.
I wouldn't pay any money for soft rock phosphate, but what I will do is collect up bones from barbecues, potlucks, and picnics and save them until I do a biochar burn. Throw the bones in with the organic matter to be charred and you end up with bone char, a very useful source of phosphorous in the garden.
collect up bones from barbecues, potlucks, and picnics and save them
And, for quantity, another source is your local butcher. The guy who does whole pigs & deer, etc.
Slaughter houses sell their bones, but small, independent butchers seldom have the facilities to process and freeze them (to keep them from stinking up their shop). Quite often, they are willing to give you as many as you want. Saves them time and money.
Whenever I ask my butcher for bones, he asks me "For soup, or your dog?" An almost endless (free) supply of either.
Thanks for you advice. There is just one problem— I have also heard that in a soil with a pH of 7 or above that bone meal or char would behave similarly to soft phosphate rock. Is this true? (for either) or would the fungi be able to feed the plants regardless of the pH?
But if it would be available, I like the idea of free bones.