ARABLE LAND 



also earths and salts. It affords food 

 to plants. It is diminished by the 

 process of vcifetatioti, and wasted by 

 being carried into the ocean by the 

 waters, or it is carried into the atmo- 

 sphere by the agency of the oxygen 

 of the air, which converts it into gas- 

 eous matter, chiedy carbonic acid. 



Hunuis, in ti»e stale in whicli it is 

 usually found in the eartii, is not sol- 

 uble in water, and we might have 

 some difficulty in comprehending how 

 it enters into the minute vessels of 

 the roots of plants ; but here the ad- 

 mirable provision of nature may be 

 observed. Humus is insoluble and 

 antiseptic ; it resists farther decom- 

 position in itself, and in other sub- 

 stances in contact with it. It re- 

 mains for a long lime in the earth un- 

 impaired ; but no sooner is it brought 

 into contact with the atmosphere by 

 the process of cultivation, than an 

 action begins. Part of its carbon, 

 uniting with the oxygen of the atmo- 

 sphere, produces carbonic acid, which 

 the green parts of plants readily ab- 

 sorb ; while its hydrogen, with the 

 same, forms water, without which 

 plants cannot live ; and in very warm 

 climates, where this process goes on 

 more rapidly, the moisture thus produ- 

 ced keeps up vegetable life when rains 

 and dews fail. The residue becomes 

 a soluble extract, and in that state is 

 taken up readily l)y the fibres of the 

 roots. Hence we see the great impor- 

 tance of frequenily stirring the sur- 

 face of the earth between vegeta- 

 bles. 



We can now readily understand 

 the great importance of humus, and 

 of tiiose rich manures which are 

 readily converted into it, when not 

 immediately absorbed by plants. But 

 it has still another property, highly 

 important to fertility : it renders stiff 

 clays porous, and consolidates loose 

 sands. It does so more than lime or 

 any other earth. Hence a soil with 

 a considerable portion of humus is 

 much more fertile than the quantity 

 of alumina or of sand in its compo- 

 sit'jn would lead one to expect, as 

 we shall see when we come to the 

 analysis of soils of known fertility ; 

 84 



and we see the great advantage of 

 animal and vegetable manures, not 

 only as nourishment to vegetables, 

 but as mechanical improvers of the 

 texture of soils. 



The greatest enemy of humus is 



stagnant water : it renders it inert 



and astringent, as we see in peat ; 



and soils abounding with vegetable 



' matters, from which water is not 



properly drained, become sour, as is 



I very justly said, and produce only 



I rushes and other useless and unpai- 



'. atable plants. The remedy is simple 



and obvious : drain well, and neutral- 



' ize the acid wiih lime or marl ; by 



i these means abundant fertility will 



I be restored. 



j In very light soils humus is seldom 

 found in any quantity, being too much 

 exposed to the air, and rapidly de- 

 I composed ; the extract is washed 

 j through them by the waters, and, as 

 they waste manure rapidly, they are 

 called hungry. Such soils are very un- 

 profitable until they are improved and 

 consolidated by clay or marl, which 

 makes them retain their moisture. 



With calcareous earths humus acts, 

 well, provided they are pulverized 

 and of sufficient depth. 



In order to ascertain the probable 

 fertility of a soil, it is very useful to 

 analyze it, and find out the propor- 

 tion of its component parts. To do 

 this with great accuracy requires the 

 knowledge of an experienced chem- 

 ist. See Analysis. 



Mr. Thaer has given a classifica- 

 tion of soils of known qualities, which 

 we think worthy of notice. It is as 

 follows ; 



