34 RELATION OF LIME AND MAGNESIA TO PLANT GROWTH. 
liming. An undesirable increase of magnesia is often caused by the 
manuring with crude potassium salts of Stassfurt, as above pointed 
out. In this case also liming furnishes the remedy.’ 
This correction grows in importance with the absolute amount of 
magnesia contained in the soils,” since the poisonous effect of magnesia 
grows with the concentration. It is therefore clear that the determi- 
nation and balancing of the available amount of magnesia and lime in 
the soils is necessary for successful farming on apparently infertile 
soils. The amount, however, available for the next crop is not 
obtained by treating the entire soil with concentrated hydrochloric 
acid, since compounds are thereby dissolved which the roots can not 
utilize before their further disintegration or final distribution. The 
system of Dyer, consisting in the treatment of the soil with 1 per 
cent citric acid for seven days after ‘‘neutralization” of the carbon- 
ates, 1s apparently more in accord with the dissolving power of the 
roots, but Lemmermann’® has shown for potassa that even 5 per cent 
hydrochloric acid does not extract all that is available for certain 
plants. This may hold good also for lime and magnesia whenever 
they are present, not as carbonates, but wholly or partially as hydrous 
silicates. Since Daikuhara* has observed for phosphoric acid that 
soils treated with acetic, citric, or oxalic acids in 1 per cent solution 
are only partially deprived of the phosphoric acid available for barley, 
it will be best to follow the system of Thoms—that is, to treat the soil 
with a hydrochloric acid of 10 per cent. However, with that modifi- 
cation only that portion of a soil that passes through a 0.5 cm. sieve 
is thus treated,’ and the percentage in this fine sand, silt, and clay 
only is determined. It will be best to mix 200 grams of this fine 
portion in a 1-liter flask with 400 ¢c.c. of the 10 per cent hydrochloric 
acid, and let the mixture stand, with frequent shaking, for one day at 
the ordinary temperature. Water is then added to fill up to 1 liter, 
and, after well mixing and filtering, certain portions of the filtrate 
1P. Wagner very correctly remarks (Jahresbericht fir Agrikultur Chemie, 1897, 
p. 254): ‘‘The successful application of the crude Stassfurt salts containing chlorid 
and sulphate of magnesium presumes a soil rich in carbonate of calcium. More 
attention has to be paid to the magnesia content of the Stassfurt salts than has 
hitherto been the case. Under certain circumstances the magnesia content can act 
very favorably, while a too rich manuring with magnesia salts may prove injurious.”’ 
This is exactly what follows from the writer’s theory published five years previous 
to Wagner’s utterances. 
* The excess of magnesia over lime in soils never reaches such proportions as, on 
the other hand, the excess of lime over magnesia may do. Thus, there frequently 
exist soils with 20 per cent to 40 per cent of carbonate of lime, while soils with over 
5 per cent of carbonate of magnesia are rarely found. 
3Landw. Vers. Stat., Vol. XLIX, S 30. 
‘Private communication. 
> Still more correct results might be obtained by using a 0.2 cm. sieve, but this 
must be determined by further tests. 
