Relation of the Soil Solution to the Soil Extract 



39i 



In Table IV the results on extracts obtained by these different methods 

 are presented, all calculated to parts per million of the dry soil, so that 

 comparisons may be made on the same basis. 



If the total solids are considered, it will be noted that the magnitudes 

 are very similar except in the case of the 1 to 5 extract shaken for 1 week. 

 More potassium is extracted by a 1 to 5 extract than by a 1 to 1 extract, 

 but the quantities are essentially the same whether the time is 40 minutes 

 or 1 week. The calcium, magnesium, and sulphate may be appreciably 

 increased during the week's contact when the proportion is 1 to 5 but 

 not when the proportion is 1 to 1 . Nitrate is not greatly changed in a 1 

 to 5 extract by the increased time of extraction. In the 1 to 1 extract in 

 one case of a heavy- textured soil there is a decrease after 1 week, and in 

 another case of a light-textured soil there is an increase. Very probably 

 biological action is concerned in these changes. Phosphate is increased 

 markedly in the 1 to 5 extract as compared with the 1 to 1 extract. 



Several fairly definite deductions may be drawn from the data just 

 presented. When a smaller proportion of water to soil is used, as 1 to 1 , 

 there is only slight increase in dissolved substances with the period of 1 

 week as compared with a shorter period, although some changes in nitrate 

 may result from biological action. There would not seem, therefore, to 

 be any advantage in the longer period of contact; in fact the biological 

 changes would make such a procedure undesirable. In the 1 to 5 ex- 

 tracts there is a significantly increased solution of various elements (par- 

 ticularly calcium and magnesium) during the period of a week. This 

 must be due to the solution of soil minerals, more of which are dissolved 

 in the 1 to 5 extract because of the greater dilution of the solvent, as 

 previously explained. Phosphate is in a somewhat different category 

 from the other elements in that the total quantity dissolved is some- 

 what directly dependent upon the volume of the solvent. As was stated 

 before, to a certain extent the solution is always saturated with respect 

 to phosphate. 



Table V. — Comparison of extracts of soil prepared by various methods 



Soil 

 No. 



Time of extraction. 



Ratio of 

 soil to 

 water. 



Composition of extracts calculated to basis of water-free soil. 



Total 



Solids. 



Potas- 

 sium 

 (K). 



Cal- 

 cium 



(Ca). 



Magne- 

 sium 

 (Mg). 



Nitrate 

 (NOs). 



Phos- 

 phate 

 (PO4). 



Sul- 

 phate 

 (SO4). 



40 minutes 



1 week 



40 minutes 



1 week 



40 minutes 



1 week 



40 minutes 



1 week 



40 minutes 



1 week 



40 minutes 

 1 week 



P. p. m. 



680 

 612 

 636 

 l>°34 

 SIO 

 562 

 5°3 

 806 

 532 

 524 

 S82 

 836 



P. p.m. 

 24 



26 

 38 



P. p. VI. 

 62 



47 



69 



P. p.m. 

 26 



P. p. m. 



80 



54 

 128 

 126 



68 

 114 

 114 

 128 



78 



63 

 116 

 145 



P. p. m. 



P. p. m. 



60 

 79 



