96 THE SOIL. 



certainty we know that chloride of sodium, nitrate of 

 soda, salts of ammonia, humus, and lime, beside the ac- 

 tion peculiar to their elements, perform also a kind of 

 digestive function comparable to that of the stomach in 

 animals, and in which they may partly replace each 

 other. These substances, therefore, act beneficially upon 

 those kinds of soil only in which there is a defect, not 

 in the quantity, but in the form and condition of the 

 nutritive elements ; and they may accordingly in their 

 permanent action be replaced by a mechanical commi- 

 nution, or exceedingly fine pulverisation of the soil. 



The true art of the practical farmer consists in 

 rightly discriminating the means which must be ap- 

 plied to make the nutritive elements in his field effect- 

 ive, and in distinguishing these means from others 

 which serve to keep up the durable fertility of the land. 

 He must take the greatest care that the physical condi- 

 tion of his ground be such as to permit the smallest 

 roots to reach those places where nutriment is found. 

 'The ground must not be so cohesive as to prevent the 

 spreading of the roots. 



In a stiff, heavy soil, plants with fine, slender roots 

 will never thrive well, even though the supply of nutri- 

 tive ^substances be ample ; and in these circumstances, 

 the beneficial influence of green manure and fresh sta- 

 ble dung is unmistakeable. The mechanical condition 

 of the soil is, in fact, altered in a remarkable w r ay by 

 the ploughing in of plants and their remains. A stiff 

 soil loses thereby its cohesion, becoming more friable 

 and crumbling, than it would be by the most diligent- 

 ploughing. In a sandy soil, on the other hand, a cer- 

 tain cohesion is hereby produced. Every stern and 

 leaf of the green-manure plants ploughed in, opens up, 

 by its decay, a road by which the delicate roots of the 

 cereals may ramify in all directions to seek their food. 

 Here, too, we must always remember, that the effect 

 calculated to be produced is a question of degree. In 

 many fields, the roots left in the soil of a fine crop of 

 green forage plants will suffice to improve a succeeding 

 cereal crop ; and a field from which a crop of lupines 



