the approximate weight of a soil 6^i In, over an aere |

of land, while 1,000,000 Ib. is as the of a |

muck soil over the same area). *

Analytical Methods.—The methods for studying th*.1 $^

soil may be considered under the : |,'

(a) Complete analysis. | ,

(6) Potential plant |

(c) Available food. ^

Complete Analysis.—The inorganic is ^

by fusing the soil with alkali carbonates, the ||;

forming alkali silicates which can be in fe'

acid. From this solution the total constituents, i

the exception of carbon dioxide, sulphur, \

may be determined. The latter group, as well as |

nitrogen, phosphorus, and organic matter, are In /

separate samples. !

Potential Plant Food.—This is by the ,/

soil in hydrochloric acid of constant (specific

gravity 1.115, containing about 23 per of HC1), the

ratio of 1 part of soil to 10 of acid, thus the

or partial decomposition of soil minerals. This formerly
the official method.

Available Plant Food.—This is the part of the supply

which is immediately available to plants. There are many ' f

natural agencies tending to make plant food as >

bacterial action, plant decay and root acidity, it is /'

to determine the part played by any one, especially by I »

acids. After making an extensive study of the acidity of £f \

plant roots it was suggested by Dyer in 1894 solubility in a J ,

1-per cent solution of citric acid most nearly measured the t *

availability, as indicated by the ability of to |;//

absorb material from the soil. Various other solvents have £, [

tried, such as distilled water, carbonated distilled K'

acid, aspartic acid and fifth-normal hydrochloric nitric acids. ^

The latter seems to give more consistent results on many soils fj

than does citric acid. However, all lalx>ratory results obtained |'^!

by the use of weak solvents are only approximations to the action |j i.
of natural solvents in the soil

1