54 SOIL AN IMPORTANT FACTOR 



The full meaning of good tilth and its importance as regards the 



seed and the young plant may be gained by studying the following 



brief outline. 



( a. Entrance of air. 

 L Mellowness of seed bed to ] h. Stem penetration, 

 pernut of [ c. Root penetration. 



Good tilth implies I 2 Firmness of seed bed to fa. Between soil particles. 



secure good contact (Fig \ b. Between seed and soil 

 [ 20) [c. Between roots and soil. 



Whenever a seed bed is too loose, therefore, it should be made 

 firm even before planting, by the use of a roller, so that there will 

 be good contact between the soil particles, between the seed and 

 the soil when the seed is planted, and later on between the roots 

 and the soil. The soil should be &m enough to make this good 

 contact possible, yet not so compact as to prevent the entrance of 

 air and the easy penetration of the stem and roots (Figs. 22 and 23) . 



Factors Affecting the Development of Good Tilth. — The devel- 

 opment of good tilth through cultivation depends largely on the 

 texture, structure, and moisture content of the soil. Heavy soils 

 usually require careful management to secure good tilth. It is not 

 difficult to develop a good seed bed on sandy and loamy soils, 

 and on soils having a crummy or granular structure. 



A hard and lumpy or heavy clay if plowed in the fall will develop 

 good tilth of itself as a result of the freezing and thawing during 

 winter and early spring. 



All soils work up much better when they contain a proper 

 amount of moisture. Plowing or cultivatmg a heavy soil when 

 too wet invariably results in poor tilth, in that the soil becomes 

 hard and lumpy. 



Plant-food Elements. — ^The so-called "raw materials'' taken 

 in by plants contain the essential elements which enter into the 

 composition of the foods made by them, hence the term "plant- 

 food elements." 



Availability of Plant-food Elements. — ^Nitrogen and the mineral 

 elements enter the plants through their roots in the form of com- 

 pounds or salts in solution.^ These elements must be in the form 

 of soluble compounds, or in liquid form, before they can become 

 available to the plants. In this respect we speak of "availability" 

 of the plant-food elements. 



^ Water enters a plant through its roots by a process called ''osmosis." 

 The entrance of salts in solution may be termed "diffusion." 



