In this instance the barrenness of the soil is distinctly traceable to the deficiency of phosphoric acid, sulphuric acid, and chlorine. There is also a remarkably large quantity of oxide of iron, which, when acted on by the humic acid, is well known to be highly prejudicial to vegetation, and that this took place was shown by the fact that the drains, a couple of months after being laid, were almost stopped up by humate of iron. Still more striking are the following analyses:—

Moorland soil near Aurich, East Friesland. Sandy soil near Wettingen. Soil from near Muhlhausen.
Silica and sand 70·576 96·000 77·490
Alumina 1·050 0·500 9·490
Oxide of iron 0·252 2·000 5·800
Oxide of manganese } trace { trace 0·105
Lime } { 0·001 0·866
Magnesia 0·012 trace 0·728
Potash } trace trace
Soda }
Phosphoric acid } 0·003
Sulphuric acid } trace
Carbonic acid ... ... 0·200
Chlorine trace trace trace
Humic acid 11·910 0·200 0·732
Insoluble humus 16·200 1·299 0·200
Water ... ... 4·096
100·000 100·000 100·000

The results contained in these analyses are peculiarly remarkable, for they indicate the almost total absence of all those substances which the plant requires. They must, however, be considered as in a great measure exceptional cases, as it is but rarely that so large a number of constituents is absent, and it is much more frequent to find the deficiency restricted to one or two substances. They are illustrations of barrenness dependent on different circumstances. The first shows the unimportance of the organic matters of the soil, which are here unusually abundant, without in any way counteracting the infertility dependent on the absence of the other constituents. The second is that of a nearly pure sand; and the third, though it contains a greater number of the essential ingredients of the ash, is still rendered unfruitful by the deficiency of alkalies, sulphuric acid, and chlorine.

An examination of the foregoing analyses indicates pretty clearly some of the conditions of fertility of the soil, which must obviously contain all the constituents of the plants destined to grow upon it. But it by no means exhausts the subject, for numerous instances are known of soils containing all the essential elements of plants in abundance, but on which they nevertheless refuse to grow. In these instances the defect is due either to the presence of some substance injurious to the plant, or to the state of combination of those it requires being such as to prevent their absorption. Reference has been already made to the bad effects of protoxide of iron, and it would appear that organic matter is sometimes injurious. Even water, by excluding air, and so preventing those decompositions which play so important a part in liberating the essential elements from their more permanent compounds, although it cannot render a soil absolutely barren, not unfrequently materially diminishes its fertility.

The state of combination of the soil constituents unquestionably exercise a most important influence on its fertility. That this must be the case is an inference which may be easily drawn from the statements already made regarding the different minerals from which it is directly or indirectly produced. If, for instance, a soil consist to a large extent of mica, it would be found on analysis to contain abundance of potash and some other matters, and yet our knowledge of the difficulty with which that mineral is decomposed, would enable us to pronounce unfavourably of the soil; and practical experience here fully confirms the scientific inference.

The forms of combination most favourable to fertility is a subject on which our information is at present comparatively limited. It was at one time believed that solubility in water was an indispensable requisite, but recent investigations appear to lead to a directly contrary conclusion. The analyses of soils already given, show that the part directly soluble in water embraces only a certain number of the constituents of the plant, and of those dissolved the quantity is very small. This becomes still more apparent if we estimate from the analyses the actual quantities of those substances contained in an acre of soil. It is generally assumed that the soil on an imperial acre of land 10 inches deep weighs in round numbers about 1000 tons; and calculating from this, we find that the quantity of potash soluble in water in the Mid-Lothian wheat soil, amounts to no more than 70 lb. per acre. But a crop of hay carries off from the soil about 38 lb. of potash, and one of turnips, including tops, not less than 200 lb., so that if only the matters soluble in water could be taken up by the plant, such soils could not possess the amount of fertility which they are actually found to have.

It is to be remembered, also, that in these analyses the experiment is made under the most favourable circumstances for ascertaining the whole quantity of matters which are capable of dissolving in water; that practically dissolved is very different. The recent analysis by Krocker and Way of the drainage water of soils afford a means of estimating this. Way found in one gallon of the drainage water from seven different fields, collected in the end of December—

1 2 3 4 5 6 7
Potash,tracetrace 0·02 0·05trace 0·22trace
Soda, 1·00 2·17 2·26 0·87 1·42 1·40 3·20
Lime, 4·85 7·19 6·05 2·26 2·52 5·8213·00
Magnesia, 0·68 2·32 2·48 0·41 0·21 0·93 2·50
Iron and Alumina, 0·40 0·05 0·10 none 1·30 0·35 0·50
Silica, 0·95 0·45 0·55 1·20 1·80 0·65 0·85
Chlorine, 0·70 1·10 1·27 0·81 1·26 1·21 2·62
Sulphuric acid, 1·65 5·15 4·40 1·71 1·29 3·12 9·51
Phosphoric acid,trace 0·12tracetrace 0·08 0·06 0·12
Ammonia, 0·018 0·018 0·018 0·012 0·018 0·006 0·018
Nitric acid, 7·1714·7412·72 1·95 3·45 8·0511·45
Organic matter, 7·00 7·4012·50 5·60 5·70 5·80 7·40

Some of the soils from which these waters were obtained had been manured with unusually large quantities of nitrogenous matters, which accounts for the large amount of nitric acid, as well as the lime which that acid has extracted. Dr. Krocker's analyses were made on soils less highly manured, and the water was collected in summer.