12 FERTILIZERS. 



HUMUS. 



There is, however, a value in barn manure in addition 

 to its fertilizing properties. Its bulk has a mechanical 

 effect on the soil, improving heavy soils, and lightening 

 the texture of all soils, a fact of especial value to market 

 gardeners in their early crops. By its partial decomposi- 

 tion, it adds to the mass of dark-brown earth which we 

 so especially notice in old gardens, and which goes under 

 the name of humus. Humus is dead vegetable and animal 

 matter in process of decay. In the surface twelve inches 

 of good soil, there is, in a latent condition, about fifteen 

 hundred pounds of phosphoric acid, fifteen hundred pounds 

 of potash, and seventeen hundred pounds of lime. Car- 

 bonic acid changes these into plant-food. Now, humus, 

 by its decay, develops carbonic acid, and so brings about 

 the decomposition of this latent food. Wet weather favors 

 this action. That carbonic acid has this power to set free 

 plant-food in the soil, has been proved by the experiments 

 of Professor Stockhardt. Our crops take up only a small 

 portion of the fertilizers we apply before the nutrient sub- 

 stances they contain become insoluble. The humus keeps 

 them in a soluble condition, which is an argument for the 

 use of barn manure, muck, or the ploughing-under of sod 

 or green crops, in connection with the use of fertilizers. 

 It acts as a sponge, to absorb and hold moisture in low, 

 black soils, which are made up of dead vegetable matter 

 in a state of semi-decay, halfway towards coal, a carbo- 

 naceous mass of stems, roots, and leaves. Burnt, it makes 

 an ashes red, from the presence of iron, having but one- 

 sixth the potash to be found in hard-wood ashes. The 

 trouble with the humus of soil of a mucky nature for till- 

 age purposes is, that when dry it takes up water very 

 slowly ; and it takes, therefore, a good deal of rain tc 



