CHAPTER VIII. 



SOILS AND MANURES. 



The fundamental secret of continued success in farming is the maintenance 

 of soil fertility. — Mr. Runciman, President of the Board of Agriculture. 



Maize requires a better quality of land, and a higher grade of farming, than 

 any other of the great staple crops. — Prof. T. N. Carver. 



By dung we are limited to the quantity of it we can procure, which in most 

 places is too scanty. But by tillage we can enlarge our field of subterranean pas- 

 ture without limitation. — Jethro Tull. 



chap. 296. The Soil. — Soil is the medium in which plants grow 



• and from which they draw the chemical substances used in the 

 processes of growth. Soils are produced by the weathering 

 and decomposition of rocks. They vary in texture, and are 

 described as stony, sandy, loamy, or clayey ; a loam is inter- 

 mediate between sand and clay. 



Soils vary in chemical composition according to the nature 

 of the rocks from which they have been derived, and may thus 

 vary in the amount of plant-food which they contain. Ninety 

 to 95 per cent of most of the fertile soils consist of the following 

 substances: phosphoric acid, potash, lime, soda, magnesia, iron 

 oxide, sulphuric acid, chlorine, silica, and alumina, which, how- 

 ever, do not usually exist in a free state. The remaining 10 

 or 5 per cent is made up of humus or decayed vegetable matter 

 containing nitrogen. Sometimes a fertile soil has only 2 or 3 

 per cent of humus, while in other cases it may contain 25 and 

 even 50 per cent. Nitrogen is also contained in rain-water, 

 in varying amounts, and is further added to the soil by the 

 action of nitrifying bacteria living on the roots of leguminose 

 plants (II 311). 



Both texture and chemical composition of the soil have an 

 important bearing on plant growth. 



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