Tilth and Tillage of the Soil 1761 



means of keeping the soil in good tilth may be obtained by a review of 

 the factors influencing granulation : 



1. Adequate drainage is the .most fundamental of these. It is impossible 

 to keep a poorly drained soil in good tilth. Such a soil is naturally inclined 

 to puddle and compact, and when dry works up into a rough, lumpy 

 condition. Continual wetness breaks down the granular aggregates by 

 dissolving the cementing material, and permits the particles to settle 

 together. The first step toward improvement of soil that is too compact 

 is provision for good drainage by some means, preferably by tile under- 

 drains. 



Drainage quickly removes excess water and permits a reasonable amount 

 of drying, which results in cutting and granulating the soil by means of 

 checks and cracks. Without any other treatment, drainage will loosen 

 the soil and provide an improved circulation of water and gases through- 

 out the earth mass. In proof of this is the observation of farmers that 

 underdrains in heavy soil gradually increase in efficiency over a period 

 of years. This mode of action has been described as a " slacking " of the 

 soil, although technically it is a different process. The earth seems to 

 fall apart and loosen to such an extent that certain persons have thought 

 they noticed an elevation of the surface adjacent to the lines of drain. 

 Too much emphasis cannot be placed on the fundamental value of 

 drainage in improving the physical condition of compact soils. 



2. Tillage of soil that contains only capillary (film) water is very helpful. 

 If the soil is cither too wet or too dry the best results cannot be obtained. 

 (Fig. 90.) That nicely moist condition in which a mass of moist soil 

 pressed in the hand will hold its form but will not show free water, is the 

 right stage for proper tillage. When too dry, a soil breaks into chunks, or 

 clods, that must be broken down. 



3. Plenty of decaying organic matter in the form of humus is very 

 helpful in developing good tilth. Humus is a dark-colored, gelatinous 

 substance that in many ways helps to produce granular structure. The 

 tendency of soils to settle and bake after years of cultivation is often 

 due to exhaustion of the organic matter. This in turn reacts on the physical 

 and drainage condition of the soil in a way which is doubly injurious. 

 The maintenance of humus in the soil is one of the most effective means 

 of improving the tilth. This applies to sandy land quite as much as to 

 clay land, but in sand the mode of action is different from the process of 

 granulation. 



4. Lime has a peculiar effect on clay soils. The fine particles are 

 thrown together in groups or floccules and when the soil dries these become 

 granules. Clay soils rich in lime carbonate have sometimes been mistaken 

 for sandy soils because of this action. Clay soils that have been granulated 



