We will now take under consideration that part of the soil on which depends its ability to supply food to the plant. This portion rarely constitutes more than five or ten per cent. of the entire soil, sometimes less--and it has no reference to the sand, clay, and vegetable matters which they contain. From analyses of many fertile soils, and of others which are barren or of poorer quality, it has been ascertained that the presence of certain ingredients is necessary to fertility. This may be better explained by the assistance of the following table: ---------------------------+--------------+-------------+---------- In one hundred pounds. | Soil fertile | Good | Barren. | without | wheat soil. | | manure. | | ---------------------------+--------------+-------------+---------- Organic matter, | 9.7 | 7.0 | 4.0 Silica (sand), | 64.8 | 74.3 | 77.8 Alumina (clay), | 5.7 | 5.5 | 9.1 Lime, | 5.9 | 1.4 | .4 Magnesia, | .9 | .7 | .1 Oxide of iron, | 6.1 | 4.7 | 8.1 Oxide of manganese, | .1 | | .1 Potash, | .2 | 1.7 | Soda, | .4 | .7 | Chlorine, | .2 | .1 | Sulphuric acid, | .2 | .1 | Phosphoric acid, | .4 | .1-1/2 | Carbonic acid, | 4.0 | | Loss during the analysis | 1.4 | 3.6-1/2 | .4 +--------------+-------------+---------- |100.0 |100.0 |100.0 ---------------------------+--------------+-------------+---------- [What can you say of the soils represented in the table of analyses? What proportion of the fertilizing ingredients is required? If the soil represented in the third column contained all the ingredients required except potash and soda, would it be fertile? What would be necessary to make it so? What is the reason for this? What are the offices performed by the inorganic part of soils?]