Introduction to the Principles of Soil Fertility 1765 



sufficient water is not retained, or is unavailable, ventilation is poor, the 

 growth of the microscopic organisms that contribute to fertility is hindered, 

 and the plant-food that the soil may contain is largely unavailable. 



Through the fineness of the soil, and its tilth, or condition of granula- 

 tion, all these properties are largely regulated; and the function of tillage 

 is to exercise some measure of control over them. But if a soil is too fiill 

 of water, it has poor ventilation, and, when tilled, is inclined to run 

 together and become puddled and hard. Hence reasonable drainage is 

 essential to good tillage. 



The proportion of humus, or well-decayed organic material, has a great 

 influence on the tilth of the soil. Not only does the humus help to keep 

 the soil loose and friable, but also it makes the color dark; thereby the 

 soil better absorbs the rays of the sun, which results in a higher average 

 soil temperature. Humus is also the chief storehouse of nitrogenous 

 plant-food in the soil. The successful farmer has always assigned great 

 value to the presence of this constituent in the soil, and its gradual exhaus- 

 tion under unwise management is one of the most noticeable changes 

 in the process of soil exhaustion. In fact, soil exhaustion frequently 

 means merely a change to such a bad physical condition that the soil 

 camiot carry on its proper functions, and the plant-food that may be 

 present is therefore not available. 



Plants use large quantities of water dtuing their growth, and practically 

 aU of this must come from the soil. It is held in the pores in the soil, 

 much as a sponge retains water. 



In all sections of New York the rainfall is sufficient to produce maximum 

 crop yields if the water can all be used effectively. Not only must the 

 soil be able to collect and hold this water in forms that plants can use, 

 but also loss of the water by evaporation must be prevented as far as pos- 

 sible by the maintenance of a mulch. Tillage at the right time and in 

 the right manner is an important aid in securing this result. An intimate 

 understanding of all the processes of moisture retention, movement, and 

 loss, together with the means for their control, is essential to the best 

 utilization of the rainfall. 



The adjustment of the water supply in the soil largely controls the 

 ventilation of the soil, which is essential to the growth of the beneficial 

 forms of soil organisms and to the penetration of plant roots. 



The amount of water in the soil, and the color of the soil, largely regulate 

 the soil temperature. 



Plants use ten elements as food. These are carbon, hydrogen, oxygen, 

 nitrogen, potassium, phosphorus, sulfur, calcium, magnesium, and iron. 

 The first three of these are obtained from the air and from water. The 

 last six are obtained entirely from the rock particles of the soil. Nitrogen 



