MANURES. 156 



just high enough to brown the paper slightly; then 

 weigh out and put into an iron ladle 100 ounces ; heat 

 it to a red heat, and keep it hot till all the black color 

 has disappeared ; cool and weigh. The organic matter 

 will have burned away. If it new weigh 99 ounces, 

 his soil contains 1 per cent, of organic matter ; if 98, 



2 per cent., and so on. A soil should contain certainly 

 as much as 2 per cent. ; and it is well if it contain 2 or 



3 times as much. 



MODES OF RESTORING ORGANIC MATTER TO A 

 SOIL. 



290. When the organic matter has become deficient 

 in a soil, there are three ways of restoring it : 1st. By 

 laying it down to grass, and pasturing it for several 

 years, till it has become thickly turfed over. 2nd. By 

 ploughing in green crops. If not entirely exhausted, it 

 may be ploughed deeply and sowed with rye, or oats 

 and clover seed. Clover roots are inclined to run deeply 

 in the ground. While the clover is growing, it draws 

 for organic matter largely from the air ; and at the 

 same time, if there are valuable salts in the subsoil, it 

 brings them up to furnish the mineral part of the crop. 

 If, when fully grown, it be ploughed in, it not only sup- 

 plies the soil with organic matter taken from the air, 

 but with saline matters drawn up from the subsoil. 

 If a large part of the clover be fed off by cattle, their 

 droppings, being returned to the surface, will nearly 

 repay the soil for the clover eaten ; and then, if the re- 

 mainder be ploughed in late in autumn, the effect is 

 nearly the same. 3rd. By putting into the soil large 



