196 Fruit-growing in Arid Regions 



change in organic matter is no doubt begun by soil or- 

 ganisms, while the later stages are probably of a chemical 

 nature. 



The decay that results in humus takes place at moderate 

 temperatures. Organisms do not develop in a low tem- 

 perature, and at a high temperature oxidation or burning 

 results. An apparent contradiction to this statement 

 is found in the difficulty with which unrotted stable 

 manure decays when plowed into land, if moisture is 

 not abundant. The lack of moisture probably prevents 

 the development of bacteria in sufficient numbers to begin 

 decay, consequently the chemical changes that result in 

 burning do not occur. The presence of such material is 

 a detriment to growing plants as it keeps the soil so open 

 that an undue amount of moisture is permitted to escape. 

 This effect is so noticeable that many of the so-called 

 dry farmers make no use of stable manure. This wanton 

 waste might easily be prevented by composting, as there 

 is sufficient moisture in the rain and snow thoroughly to 

 rot manure treated in this way. 



The compound resulting after organic decay is com- 

 pleted is humus. Such decay results in a dark-colored 

 material, without organic structure, soluble in alkalies 

 after the lime has been 'removed. Humus gives a dark 

 "rich" color to otherwise light-colored soils. It is com- 

 plex in composition. It is especially important as being 

 a reservoir of nitrogen. Much of the nitrogen that is 

 brought to the soil by leguminous plants, as well as that 

 which is stored in the plant, in the processes of growth, 

 is not available to growing plants until the humus stage is 

 reached. 



