56 Report of the Acting Director and Chemist of the 



(1) Cylay has the power of absorbing and retaining a large amount 

 of water, thus preserving a sufficient amount of moisture in the soil. 

 Clay has the power also of holding ammonia and some mineral 

 salts and again giving them up to plants. Claj', therefore, acts on 

 the available elements of the soil as a sort of regulating material, 

 retaining or yielding them by turns as the earth passes from a state 

 of drought to one of excessive moisture. 



(2) 8and serves, when mixed with clay, to diminish its compact- 

 ness and makes it more porous and permeable to the air. 



(3) Humus is the organic matter in the soil formed by the decay 

 of animal and vegetable matter. It is brown or black in appear- 

 ance ; leaf-mold, swamp-muck and peat are varieties of humus, diifer- 

 ing in appearance according to the condition of their origin and 

 formation. The decay of roots, the plowing under of sod and stubble, 

 and the application of manure cause the formation of humus in the 

 depths of the soil. The composition of humus is somewhat doubt- 

 ful. It is probably a variable mixture of several substances. Humus 

 is extremely valuable as an indirect fertilizer, for the following 

 reasons ; 



First. Humus absorbs water much more extensively than any 

 other ingredient of the soil, and thus promotes moisture of the soil. 



Second. Humus aids in the decomposition of the mineral matters 

 of the soil, changing unavailable into available plant-food. 



Third. Humus fixes ammonia in the soil, so as to prevent it from 

 being carried off by the rains ; it afterwards gives up this ammonia 

 to plants. Humus is, therefore, a very desirable constituent of the 

 soil, and the beneficial effects of stable-manure and green manure 

 are often doubtless due, in no small degree, to the abundance of 

 humus which they furnish to the soil. 



Fourth. Humus improves the mechanical condition of heavy soils 

 by making them lighter, more porous and less adhesive. ' It also is 

 helpful on sandy soils, serving to bind together the loose particles of 

 soil, enabling it to i-etain moisture and preventing excessive leach- 

 ing of plant-food. 



Amount of Plant-food in Soil. — The proportion of plant-food 

 even in a fertile soil is comparatively small. One thousand pounds 

 of a good soil may contain : 



Phosphoric Acid, 1^ lbs. 

 Nitrogen, 1^ lbs. 

 Potash, 2 lbs. 



