"A" "B" "C" Silica and insoluble 71.66 82.16 69.82 Iron and aluminum oxides 6.55 6.70 12.05 Calcium oxide 4.41 .68 .85 Magnesium oxide 1.02 .06 .87 Phosphoric anhydride .18 .08 .11 Chlorine .01 .03 .03 Potassium oxide .75 .05 .72 Sodium oxide .25 .11 .94 Sulphuric anhydride .06 .39 .12 Volatile and organic matter 3.98 5.44 8.90 Moisture 9.67 3.80 6.27 Undetermined, carbonic acid, etc. 1.48 .30 .22 ------ ------ ------ 100.00 100.00 100.00 In some cases it happens that there is a sufficient quantity of an ingredient in the soil, but it is not in a sufficiently _soluble_ form to be available. It will be noticed that in the analyses quoted above the amount of the necessary constituents of the soil to plant growth is not in any case large. The nitrogen may be present in the volatile and organic matter, and upon the proportion of this complex organic matter very often depends to a great extent the fertility of the soil. Some experiments made at one of the agricultural experiment stations upon the effect of "apple stock," that is, young trees raised for nursery purposes, on the soil, showed that in eleven tons of such stock the following quantities of ingredients were removed from the soil: Silica 50.6 lbs. Phosphoric acid 21.4 " Sulphuric acid 14.3 " Chlorine 1.3 " Carbonic-acid gas 94.9 " Iron oxide 6.1 " Lime 138.6 lbs. Magnesia 23.7 " Soda 21.3 " Potash 27.1 " ----------- Total 399.3 lbs. This is no inconsiderable quantity of material to be removed by a single crop.