Chase,

The call for urine, not only human but of farm animals was made. But there is a problem with using urine to make saltpeter, it takes a very long time via a nitre-bed method. (minimum six to eight months)

"It will be seen that under the most favorable circumstances saltpetre cannot be made in any considerable quantity in less than six or eight months, and that if we commence now the preliminary process of preparing black earth, so as to insure a sufficient and permanent supply, results cannot be expected under eighteen months or two years. Let no one be discouraged by this fact, under the idea that the war may not last so long, and all their work may be thrown away. There is every prospect now of the war continuing at least several years, and of our being thrown entirely on our own resources for war materials. Besides, even if the war should be discontinued, the work is by no means lost. The method of preparing and making saltpetre-beds is precisely the most approved method of making the best manure, and all the labor and pains necessary for the preparation of black earth, and the construction of saltpetre-beds, and which I hope to induce my fellow-countrymen to undertake under the noble impulse of patriotism, ought to be annually undertaken by every planter, under the lower impulse of a wise self-interest, and would be amply rewarded in the increased production of field crops."

From...

INSTRUCTIONS FOR THE MANUFACTURE OF SALTPETRE; BY JOSEPH LECONTE, PROFESSOR OF CHEMISTRY AND GEOLOGY IN SOUTH CAROLINA COLLEGE. 1862

http://docsouth.unc.edu/imls/lecontesalt/leconte.html

Rains produced at Augusta, Ga. over 2,750,000 pounds of first-quality gunpowder, some say the best in the world at the time, before it was shutdown in 1865. About 2,065,000 pounds of that would have to be saltpeter... unless Rains had incorporated the saltpeter-less method from Europe (the Confederate Government had gotten the formula, See Civil War Naval O.R.)

I cannot believe he was using only urine based saltpeter due to the time required to produce. It had to have come from somewhere else. Texas and Georgia and I believe parts of Alabama were producing cave mined saltpeter but was that enough? The other option was through the blockade from places like India via English merchants. I know many tons of saltpeter made it through the blockade.

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David Upton