212 Bureau of Farmers' Institutes. 



sense, clay is the common name of a compound called aluminum 

 silicate. Clay soils must be handled with great care. When 

 worked in too wet condition, they are puddled and this condition 

 prevents the proper drainage of surface water. Many clay soils 

 are too compact, retaining water and not allowing plant roots to 

 penetrate easily. 



Humus. — The word humus means, in general, the organic mat- 

 ter in the soil formed by the decay of animal or vegetable ma- 

 terials. In this sense humus is a very variable substance, its com- 

 position depending upon the materials from which it is formed and 

 upon the conditions of decomposition. For example, humus formed 

 from sawdust or leaves will differ very greatly from that produced 

 by clover or cottonseed meal. Im appearance humus is brown 

 or black. Leaf-mold, swamp-muck and peat are varieties of 

 humus, differing in appearance according to the conditions of their 

 origin and formation. 



It is known that animal or vegetable matter decaying in the 

 soil forms compounds of an acid character and these organic acids 

 unite with lime, potassium and other constituents of the soil. 

 Moreover, it is known that materials rich in nitrogen, like meat 

 scraps and cottonseed meal, produce humus that not only is rich 

 in nitrogen but also has greater power to unite with the potash and 

 phosphoric acid of the soil, thus rendering them more available 

 as plant food. 



Humus is extremely valuable for the following reasons: 



1. Humus absorbs water much more extensively than any other 

 ingredient of the soil, and thus promotes the water-holding and 

 water-conserving power of the soil. 



2. Humus aids in the decomposition of the mineral matters of 

 the soil, changing unavailable into available plant food. Its ac- 

 tion in rendering available the potash and phosphoric acid of the 

 soil is of marked value. 



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

 being carried away by rains. The ammonia thus fixed is held 

 until it gradually undergoes conversion into nitrate nitrogen, in 

 which condition it is ready for immediate use as plant food. 



4. 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 retain moisture and preventing 

 excessive leaching of plant food. 



