5'2 N. H, AGR. EXPERIMENT STATION. [Bulletin 142 



surface. In some soils these water movements take place very 

 slowty. After rains the evaporation carries away more water 

 than is carried away by percolation. This is particularly true 

 of many boulder-clay soils. In other more sandy soils the water 

 percolates very rapidly and almost never stands on the surface 

 for more than a few minutes after the rain ceases. The differ- 

 ence in the soil structure affects the rate of the water move- 

 ments. The sandy soils are usually coarse-grained, with large 

 spaces between the soil grains or particles. These spaces form 

 readily accessible waterways and permit of good drainage. On 

 the other hand, the clay soils are much different. The soil 

 particles are fine and the spaces between the particles are very 

 small. The water in these soils carries very fine particles of 

 soil in suspension. As the water goes through the already 

 minute waterways portions of these small particles are left be- 

 hind and in time clog up the small spaces still more. Finally 

 the soil becomes almost impervious to water and in such places 

 "hard pan" is formed. Obviously such soils would be bene- 

 fited by anything that would cause the soil to form larger grains 

 and thus help to establish better waterways. Such things as 

 lime, gypsum, muriate of potash, etc., have much to do with this 

 flocculation. A clay soil that has been limed well will not dry 

 in hard lumps as does the same soil unlimed. On drying the 

 limed portion will be granular and porous, while the other will 

 form a compact mass. The water movements may take place 

 much more readily in the treated soil. 



The water movement in a clay soil may be easily studied in the 

 laboratory. A column of soil is prepared as in the absorption 

 experiment, which is discussed below. When pure water is al- 

 lowed to percolate through this column, it moves more and 

 more slowly until finally almost no movement occurs unless 

 effected under pressure. The watervs'ays become almost com- 

 pletely closed. On the other hand, if solutions of lime or 

 potassium salts be substituted for the pure water, the rate of 

 percolation begins to increase until finally a fair rate is again 

 established. These solutions cause the soil particles to become 

 more granular and form larger spaces for waterways. This is 

 undoubtedly the cause of a large part of the good results some- 

 times obtained when lime is applied to clay soils. In this same 



