56 N. H. AGR. EXPERIMENT STATION. [Bulletin 142 



in the moisture content. After a lapse of more time, further 

 analyses showed that the potassium was still undergoing changes. 

 These experiments show why plant food washes out of sandy 

 soils more readily than from the clay soils. What is true of 

 potassium in this respect is also true of phosphoric acid. 



As absorption experiments show, not all of the potassium is 

 rendered insoluble. A portion is left in a soluble condition. 

 This may in part be leached out and lost, but there is a con- 

 servative force which enters here and prevents a large part of 

 this apparent loss. These experiments show that for a time 

 after the application of potassium salts the amount of soluble 

 potassium may be greater than that under natural conditions. 

 However, the tendency is toward a lessened amount of soluble 

 potassium until a normal amount is finally reached. The chief 

 and most beneficial effects from fertilizers must undoubtedly be 

 obtained while this readjustment is taking place. During the 

 rainy season the tendency of the soil water and soluble plant 

 food is downward. During fair weather and a large part of 

 the growing season, the movement of the soil water is upward. 

 A great deal of the soil water evaporates from the surface and 

 leaves the soluble mineral matter behind, and very near the sur- 

 face. These processes go on continually in one direction or the 

 other and the actual soil fertility in this respect is kept very 

 nearly constant. What fertility is carried down in the rainy 

 season is carried up again in fair weather by the soil moisture. 



The soils are composed largely of mineral and to a less extent 

 of organic matter. The organic matter behaves very much as 

 does the clay or mineral portions toward the potassium salts. 

 When the organic matter is carefully extracted from soils and 

 properly washed, it has absorptive properties. Small amounts 

 of potassium are made insoluble when in contact with the 

 extracted matter. This absorptive property is more in evidence 

 when dried muck is treated with solutions of potassium salts. 

 Some mucks which were 90% organic matter have been found 

 to remove as much as one per cent, of potassium from solution. 

 The organic matter in its natural condition has a greater absorp- 

 tive capacity than it has after being extracted or separated from 

 the soil. From the nature of the organic matter, it is a very 

 important source of plant food. When it decays or is oxidized 



