158 EXPERIMENTAL FARMS. 



It is often urged that our usual method of soil analysis, using hot, strong hydro- 

 chloric acid as a solvent, only indicates the amounts of plant food that may b come 

 available, not the amounts that are iffimediately assimilable. This is true, and it is 

 certainly a drawback, but it in nowise makes the results of no value, as some would have 

 us believe. It gives, we may suppose, the maximum amounts of the mineral elements 

 present which under the influence of favourable climatic and mechanical conditions may 

 become useful to crops. It shows decisively deficiencies in any of the plant food con- 

 stituents, if such exist, and consequently affords valuable information regarding the 

 suitability of the soil for various farm crops, and, further, indicates the direction in 

 which fertilization may be economically and profitably carried on. Soils with large 

 stores of plant food, even if such be partially or largely in a locked-up condition, have 

 repeatedly been shown to have a greater agricultural value than those that furnish to 

 the same solvent less amounts. The probabilities are that, other things being equal, 

 soils of the former class will contain, or, at all events under favourable circumstances, will 

 yield, larger amounts of readily assimilable food than those possessing smaller "totals" 

 or maximums. Soils showing percentages of maximums above the average invariably 

 prove fertile, if climatic influences are favourable. We cannot argue very closely, I 

 admit, but from such an analysis we are able to predict possibilities as to productive- 

 ness, provided agencies favourable to the unlocking of soil plant food are present. 



Soil Tests for Ascertaining Available Plant Food — Pot or plot experiments are 

 as yet, the only tests that can infallibly indicate a deficiency in available fertilizing con- 

 stituents. Such methods, however, consume much time, are cumbersome, and from their 

 very nature scarcely suited to wide application. What is needed is a laboratory 

 method or methods, in addition to those we now use, which will furnish data in ac- 

 cordance with the results obtained by actual soil trial crops. This is a question that at 

 present many agricultural chemists are engaged upon, and I venture to hope that ere 

 long the renewed interest in this work will result in satisfactory methods being 

 established, both for available mineral constituents and nitrogen. 



Dr. Dyer's Work. — In March, 1894, Dr. Bernard Dyer's work on available plant 

 food in soils appeared. It was the beginning of a new era in soil analysis. Since 

 that date increased attention has been paid to this branch of research, and especially so 

 on this continent. Every year sees new and interesting data, the results of the labours 

 of agricultural chemists of the experimental stations of the United States. Dr. Dyer, 

 it will be remembered, showed, among other valuable results, that the root sap and the 

 exudation of rootlets possessed an acidity approximately equivalent to that of a one per 

 cent solution of citric acid. From this he argued that such a solution would have a 

 solvent action on the mineral constituents of the soil similar and equal to that exerted 

 by growing crops. Further, he showed that results obtained by this method were 

 strictly in line with the deductions made from the data of actual field trials. He there- 

 fore proposed that this solvent should be used to determine available potash and 

 phosphoric acid in soils. TiVorkers in the United States, members of the Association of 

 Agricultural Chemists, besides using this solvent during the past few years, have 

 proposed and worked with other solutions, such as ammonium chloride and calcium 

 chloride. None of these, however, have had the support or corrobation of expeiiments 

 to show that they were similar or comparable in their action upon the soil to the solvent 

 action of root exudations. Consequently they do not as yet appeal to agricultural 

 chemists with the same force as the solvent proposed by Dr. Dyer. 



Solvents Employed. — The solvent used by us in the determination of " total " or 

 maximum percentages of the mineral constituents has been hydrochloric acid, sp. gr. 

 1-115 (corresponding to 22-86 per cent, HCL.), 10 grms, of the air dried soil being 

 digested with 100 c. c. of the acid at the temperature of the water bath for ten hours. 



For the estimation of the " available " potash and phosphoric acid, 1 per cent, 

 citric acid solution has been employed, digesting 100 grms. of air-dried soil with 500 

 c. c. of the solvent for five hours at room temperature. 



