MANURE.

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in sucli situations are, therefore, often improved byspreading lime over the surface.

386. It is therefore of high importance to know thenature and composition of the subsoil, as well as thesurface soil ; for by a judicious use of the former, thesoil itself may frequently be very much improved, andprobably some saving effected in the quantity of manurerequired for the land.

387. A very great variety of different substances areincluded under the general name of manure. Some ofthe substances added to the soil act principally in amechanical way, improving its texture; others arechiefly valuable as sources of carbonic acid and ammonia,whilst many are useful as supplying saline and earthymatters in which the soil may be deficient. It wouldbe easy to divide all manures into these three classes; butit is more convenient to divide them simply into theorganic and the inorganic, because many manures act inall these three ways at once, improving the texture ofthe soil, and supplying carbonic acid, ammonia, andsaline matters.

388. Organic manures may in general terms be de-scribed as consisting of any kind of organic matters in astate of decay. Setting out with the knowledge thatorganic matter consists of carbon, oxygen, hydrogen,and nitrogen, it is not difficult to understand thechanges produced by its decay.

389. Whilst describing the different varieties of organicmatter, attention has constantly been drawn to the