No. 6. DEPARTMENT OF AGRICULTURE. ISl 



The nitrogen relations will be considered at a later point. 



It was noted half a century ago that the results obtained by 

 analyses such as those just given very frequently failed to throw 

 light upon questions in which the present fitness of the land for 

 producing crops in general or a particular crop were at issue, rather 

 than questions relating to permanence of fertility, and it soon came 

 to be recognized that while such analyses afforded much informa- 

 tion valuable for many purposes, there were many other purposes 

 with respect to which the analytical results were either useless or 

 misleading. There are several reasons by which this fact may be 

 accounted for: In the first place, we observe that soils are often 

 very responsive to additions of small quantities of some fertilizer 

 constituent; indeed, a very common dressing of phosphoric acid is 

 thirty pounds per acre, the amount contributed by 200 pounds of 

 dissolved phosphate rock. The soil taken to the depth of a foot 

 over an area of an acre weighs from two and one-half to four million 

 pounds. If the weight be taken as three million pounds, you will 

 perceive that the effective quantity of added phosphoric acid bears 

 no greater proportion to the entire substance than one part on one 

 hundred thousand. In the case of soluble nitrogen compounds, such 

 as nitrate of soda, we have a still more striking illustration. A 

 dressing of twenty pounds per acre is frequently found to improve 

 the early vegetation of a grain crop, yet this dressing contains but 

 three pounds of nitrogen, a weight equal to but one-millionth of that 

 of the soil. If we examine the analyticnl methods with reference to 

 the degree of refinement of which they are capable, we find that it 

 is rarely possible to secure between double determinations agree- 

 ments as close as one part in ten thousand; even such degree of 

 delicacy is far more than we can profit by, owing to the fact that the 

 errors of sampling lead to far greater differences. While, therefore, 

 analyses by strong acids have high value for certain purposes, and 

 are essential to a determination of the agricultural resources of the 

 territory, they do not furnish such information as will usually enable 

 us to i)redict what fertilizers are at present most needed in the case 

 of lands above tlie Tank of "poor." 



Chemists have therefore sought other methods in the hope of 

 obtaining some more perfect indication of the percentage availabil- 

 ity of the food constituents in their particular soils. The methods 

 have not dey)ended upon the securing of more exact information re- 

 specting the combinations in which the nutrient elements are held, 

 but simply upon the proportion in which they are given up to mild 

 solvents. For this purpose very dilute mineral acids and organic 

 acids, with a lower decomposing power have been used. Dr. Dyer, 

 at present chemist at the Royal Agricultural Society of England, 

 made a careful study of the solvent qualities of a 1 per cent, solution 

 of citric acid for this purpose, and found that by means of it he was 

 able to extract from the barleyfields of the Eothemsted Experiment 

 Station quantities of phosphoric acid and potash corresponding very 

 closely to the net amount supplied as fertilizers for a decade after 

 deducting the quantities removed by the crops. He concluded that 

 when the soil yielded less than .01 per cent, of phosphoric acid, or 

 than .005 per cent, of potash, there was not enough of these respective 

 constituents present in available combination to permit the growth 

 of a maximum crop. The application of this method in many local- 



