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



than one pound of mineral matter per two and a half tons of 

 water. This means a very dilute solution. This same phenom- 

 enon is easily reproduced in the laboratory and shows how the 

 soil removes soluble matter from solutions; or, in other words, 

 keeps the minerals in solution down to the lowest possible 

 amount. If a solution containing a known amount of potassium 

 chloride is allowed to slowly percolate through a column of soil, 

 a large part of the potassium is removed. This is shown by 

 determining the amount of potassium passed into the soil and 

 also the amount that appears in the percolate. The difference 

 represents the amount taken up by the soil. If the solution is 

 percolated slowly, nearly all of the potassium is removed from 

 the first portions. Experiments of this sort show that the 

 strong clay soils may remove large quantities of soluble potas- 

 sium. One hundred pounds of soil is capable of taking up 

 more than one pound of potassium. This is rather significant, 

 if we stop to consider just what it means. An application of 

 1 ,000 pounds of fertilizer per acre is a generous amount. About 

 20% of this, or 200 pounds, represents the amount of plant 

 food. The soil 8 inches deep over an acre weighs about 2,000,000 

 pounds. Then we have mixed one pound of plant food with 

 10,000 pounds of soil. This is just about one hundredth of 

 the amount that many soils can readily absorb or render in- 

 soluble. It is thus evident that the plant food added as fer- 

 tilizer is not likely to be easily washed from the soil. The 

 experiments in the laboratory show that the soil prevents the 

 soluble plant food from leaching deeply into the soil. Very 

 short columns of soil will remove practically all the potassium 

 from the first portions of the percolate. These solutions are 

 made up to contain only a few hundred parts of potassium per 

 million parts of water. When the potassium is once removed 

 from solution it goes into solution again only very slowly, and 

 it is not practical to try to remove it all by washing with pure 

 water. A clay soil will absorb much more potassium than a 

 sandy soil and thus, as we would expect, the potassium would 

 leach into the sub-soil more readily in the absence of clay. This 

 is one reason why barnyard manure disappears more rapidly 

 when spread on sandy soils. 



