“That is exactly what I mean.  I see that you do not like percentage any better than I do.  Really the acre is the best agricultural unit.  We buy and sell the land itself by the acre; we report crop yields at so many bushels or tons per acre; we apply manure at so many loads or tons per acre; we apply so many hundred pounds of fertilizer per acre; sow our wheat and oats at so many pecks or bushels per acre; and we ought to know the invoice of plant food in the plowed soil of an acre and the amounts carried off in the crops removed from an acre.

“Now, referring again to these figures from the forty acres of clover at two tons per acre.  If the eighty tons were burned and the ashes mixed with the surface soil on a tenth of an acre the increase per acre would be as follows: 

4,000 pounds of phosphorus 24,000 pounds of potassium 6,200 pounds of magnesium 23,400 pounds of calcium.

“These, remember, are the amounts per acre that would be added to the soil by burning the eighty tons of clover on one-tenth of an acre.

“Now compare these figures with the total amounts of the same elements contained in the common corn belt prairie soil of Illinois, which are as follows: 

1,200 pounds of phosphorus 35,000 pounds of potassium 8,600 pounds of magnesium 5,400 pounds of calcium.

“From these figures you will see that the analysis of a single sample of soil collected from a spot of ground that had sometimes received such an addition as this would be positively worse than worthless, because it would give false information, and that is much worse than no information.

“The methods of chemical analysis have been developed to a high degree of accuracy, and it is not a difficult matter to find a chemist who can make a correct analysis of the sample placed in his hands; but the chief difficulties lie, first, in securing samples of soil that will truly represent the type or types of soil on the farm; and, second, in the interpretation of the results of analysis with reference to the adoption of methods of soil improvement.”

“Is the report of the analysis as confusing with respect to other elements as with potassium and phosphorus, which, I understand, are likely to be reported in terms of potash and a ‘phosphoric acid’ that is not true phosphoric acid?”

“Still worse,” Percy replied.  “The calcium is commonly reported in terms of lime, or, as you would say, quick lime; and vet the soil may be an acid soil, like yours, and contain no lime whatever, neither as quick lime nor limestone.  I have seen an analysis reporting half a per cent. of calcium oxid, which would make five tons of quick lime in the plowed soil of an acre; whereas the soil not only contained no lime whatever, but was so acid that it needed five tons of ground limestone per acre to correct the acidity.

“The trouble is that when the chemist found calcium in the soil existing in the form of acid silicate, or calcium hydrogen silicate, he reported calcium oxid, or lime, in his analytical statement, assuming apparently that the farmer would understand that the analytical statement did not mean what it said.”