54 PRINCIPLES OF FARM PRACTICE 



. To a certain extent also, thorough tillage, practiced through 

 several seasons, and good drainage will secure a better con- 

 dition of heavy soils, by bringing about granulation. Alter- 

 nate freezing and thawing, and wetting and drying, are 

 natural means tending to produce the same results. 



It would be good farm practice to employ all four methods, 

 especially since lime, organic matter, tillage, and drainage 

 have other important uses besides that of improving clay., 



It happens that putting clay soils in the best condition 

 for handling puts them also in the best condition for plant 

 growth. Granulation increases aeration, allows roots of 

 plants to push their way more readily through the soil, and 

 promotes better drainage from the top layers, thus removing 

 the water so that the soil is more easily warmed in the spring. 



Although clay soils are naturally rich in plant-food material, 

 the supply is by no means inexhaustible. The material taken 

 out of the soil by crops must be replaced from time to time, 

 if permanent fertility is to be maintained. This applies 

 especially to organic matter, the removal of which not only 

 lowers the nitrogen content, but also affects the structure by 

 reducing granulation. Although the supply of phosphoric 

 acid is greater than in sandy soils it must be replenished, for 

 which purpose the rock-phosphate-manure method is probably 

 the most economical. In a few regions such as the limestone 

 valleys 'and uplands of central Kentucky and Tennessee, the 

 natural supply of phosphoric acid seems to be adequate. 

 Potash is generally abundant, but it may be applied to advan- 

 tage as a light dressing at the time of planting or sowing, 

 since the growth of young plants is greatly stimulated by 

 potash. 



Loam soils. Loam soils, being a mixture of sand with 

 clay and silt, have some of the properties of each. To a 



