The Science of the Soil 133 



loams are usually designated as being rich in potash, yet the addition 

 of potash salts will often give high results on such soils, showing there- 

 fore a deficiency in available potash, an entirely different thing from total 

 potash. 



Many of the food salts in the soils are so tightly held or combined 

 as to resist even long years of cultivation and weathering. 



Nowadays it is the rule to dissolve out the available salts which can 

 be immediately rendered available to the growing crops, by using for this 

 purpose a 1- per -cent solution of citric acid; this strength having been 

 estimated to correspond with the solvent action of natural forces at 

 work. 



These forces are the weak organic acids obtained from humus, the work 

 done by the beneficent and other bacteria, as well as by enzymes and 

 certain fungoid moulds, and, lastly, by the solvent action of soil water 

 impregnated with carbonic acid gas. 



It is not at all necessary for anyone to attempt a complete analysis. To 

 obtain such would mean probably months of work, and the data obtained 

 would be of very little value to the grower. What is usually done is 

 to give the quantities of lime carbonate (chalk), magnesia, nitrogen, phos- 

 phates, potash, the total contents, organic matter and humus. 



About 40 to 80 per cent of soil matter is inert and does not enter into 

 the fertilizing, but its composition determines the physical condition of a 

 soil and thus has a great bearing on cultivation. 



In reading an analysis care should be taken to note that the magnesia, 

 usually magnesium oxide (MgO), is not in excess of the lime contents, 

 or disease and various other troubles will quickly follow. It will not 

 matter how much lime carbonate is present if the magnesium oxide is 

 multiplied by 2 and then compared with lime carbonate. Sufficient of 

 the latter must be added to give a proportion equal to four of the 

 former (magnesium carbonate) to seven of the latter (lime carbonate). 



A sample of soil may be taken as follows: Cut a square about 9 in. 

 with a spade to a depth of about 1 ft.; take the whole of the soil from 

 this block and place in a box. Remove to a shed or laboratory for 

 examination. 



If the soil is rather wet, allow it to air-dry somewhat, and then work 

 through a fine sieve to remove all stones. Take a portion of the soil, say 

 \ to \ lb., and place in a beaker, tube, or even an ordinary jug. Fill 

 the vessel containing the soil three parts full with water; stir to a paste, 

 thus separating clay from sand. Allow to settle somewhat, pour off, and 

 repeat this until the added water becomes no longer turbid. Remove 

 the sand from the bottom, air-dry, and weigh, and the result will show 

 you into what class your soil fits, whether it be sand, sandy loam, 

 loam, clayey loam, or clay, the physical constituents of which are given 

 at p. 92. 



Chemical Analysis. The following is a minimum list of apparatus, 

 some of which may be evolved from ordinary articles in everyday use, but 



