Loamy soil, where sand and clay are about equally mixed.
Marl contains from five to twenty per cent. of carbonate of lime.
Calcareous soil more than twenty per cent.
Peaty soils, of course, contain large quantities of organic matter.[P]
How large a part of the soil may be used as food by plants?
What do we learn from the analyses of barren and fertile soils?
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 without manure. | Good wheat soil. | Barren. |
| 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 | .1½ | |
| Carbonic acid, | 4.0 | ||
| Loss during the analysis | 1.4 | 3.6½ | .4 |
| 100.0 | 100.0 | 100.0 |