THE MAGAZINE 
OF 
Tf)G moot OF AGRieOLTUKC, 
COLCMBC. 
Added as a Stippkment monthli/ to the ''TROPICAL AGBIGULTUHIST" 
The following pages include the Contents of the 3Iagazine o f the School of 
AgriciiUure for April : — 
Vol. v.] APRIL, 1894. [No. 10. 
SOURCES OF GAIN AND LOSS TO 
THE SOIL. 
inrTj?,*^;^ T is of paramouut importance to the 
j^vt-s® cultivator of the soil that he 
Pl^f should have a clear idea in his 
mind of the sources of gain and 
iS^^u^i.'^ 1043 to the soil he oultivates, and 
what ingredients of plant food are derived or lost 
through those sources, so that he may thereby be 
in a position to devise and adopt measures which 
may as far as possible enable. him to help the soil 
to gain and not to lose the elements of fertility. 
The sources of gain may be classified under 
various heads : — 
1. There is the land itself whicli yields 
available plant food under the action of the 
natural weathering agents. These agents — the 
atmospheric, thermometric, chemical and animal 
agents — aid in the decomposition of rocks and 
minerals, and enable them to yield soluble plant 
food. Again the land itself is made to supply 
valuable substances under the influence of various 
artificial mechanical means generally spoken of 
as " tillage,'' as well as from the result of such 
operations as draining, lining, irrigation and 
the like. 
2. The atmosphere is a source of plant food 
which mainly reaches the soil in conjunction 
with rain. By means of it moisture as rain 
aad dew is also .-jupplicil to crops. 
The atmosphere primarily consists of two 
gases, but iatermi.\od with them are various 
other substances, such as carbonic acid gas, 
ammonia, thq chlorides, sulphate^j aad nitrates 
of sodium, calcium, and ammonium, and certain 
solid impurities as dust and soot. The most 
important derivatives from the atmosphere are 
the compounds of nitrogen, the origin of which, 
however, cannot be conveniently considered 
here, 
3. Another source of gain is the residue of 
plants and crops which finally yield nitrogen, 
potash and x^hospiioric acid. 
4. There is a special source of nitrogen 
which has only of late years been recognised. 
This is the elaboration of nitrogen compounds 
from the free nitrogen of the atmosphere, by 
means of the bacteriods contained in the root 
tubercles of certain leguminous and other plants. 
5. The application of manures (natural and 
artificial fertilizers) such as cattle manure, 
guano, chemical compounds, waste products and 
green manures, directly increase the fertility 
of the soil. 
The sources of loss, on the other hand, are as 
far as can be ascertaiu';d : — 
1. Evaporation of water from the soil, and 
transpiration of water vapour by the leaves of 
plants and trees. 
2. Wash and drainage cause the loss of water 
and other ingredients which are carried away iu 
suspension and solution. The chief and most 
serious loss by these means is, however, that of 
the nitrates, which owing to their solubility are 
easily carried off in solution. Ordinary soils, 
witli a fair admixture of clay (which has a 
retentive power for these substances) do not 
sulfer any appreciable loss of phosphoric acid 
and potash by means of drainage. 
2. The removal in various ways of what is 
produced in the land is manifestly a source 
of loss to the soil, which has to be made good by 
the cultivator. 
3. Lastly, neglect on the part of the cul- 
tivator to aid tlie action of the natural forces, 
or to employ artiticial agencies which luive au 
ameliorating influence will of course tend to 
impoverish the soil by withholding the means 
by which it may be euriclied. 
