the nutriment of the soil is exhausted.

10. Draining _enables us to deepen the surface-soil_, because the
admission of air and the decay of roots render the condition of the
subsoil such that it may be brought up and mixed with the surface-soil,
without injuring _its quality_.

The second class of advantages of under-draining, arising in the removal
of the excess of water in the soil, are quite as important as those just
described.

[How does the removal of water render soils earlier in spring?

Why does it prevent the throwing out of grain in winter?

Why does it enable us to work sooner after rains?

Why does it keep off the effects of cold weather longer in the fall?]

11. _Soils are, thereby, rendered earlier in spring_, because the water,
which rendered them cold, heavy, and untillable, is earlier removed,
leaving them earlier in a growing condition.

12. _The throwing out of grain in winter_ is prevented, because the
water falling on the earth is immediately removed instead of remaining
to throw up the soil by freezing, as it always does from the upright
position taken by the particles of ice.

13. _We are enabled to work sooner after rains_, because the water
descends, and is immediately removed instead of lying to be taken off by
the slow process of evaporation, and sinking through a heavy soil.

14. _The effects of cold weather are kept off longer in the fall_,
because the excess of water is removed, which would produce an unfertile
condition on the first appearance of cold weather.

The drains also, from causes already named (3), keep the soil warmer
than before being drained, thus actually lengthening the season, by
making the soil warm enough for vegetable growth earlier in spring, and
later in autumn.

[How does it prevent lands from becoming sour?

Why does it hasten the decay of roots, and the comminution of mineral
matters?

How does it prevent the abstraction of heat from the soil?]

15. _Lands are prevented from becoming sour by the formation of acetic
acid_, etc., because these acids are produced in the soil only when the
decomposition of organic matter is arrested by the _antiseptic_
(preserving) powers of water. If the water is removed, the decomposition
of the organic matter assumes a healthy form, while the acids already
produced are neutralized by atmospheric influences, and the soil is
restored from sorrel to a condition in which it is fitted for the growth
of more valuable pl