PLANT-FOOD MATERIALS IN SOILS 



103 



required for plant growth, it is not hard to realize that there 

 must result a constant and significant loss of fertility. The 

 plant-food materials lost in largest quantity are lime, mag- 

 nesia, potash, nitrogen and sulfur. Phosphoric acid is 

 not removed in large quantity from any soil and appears 

 only in traces in the drainage water of most soils. 



120. Quantities of plant-food materials in drainage. — 

 The quantities of plant-food materials that are removed 

 from soil in the course of a year will depend on a variety of 

 conditions and, to some extent, these and the total losses 

 that may be expected are indicated by the following table, 

 which is based on the annual average loss for a period of 

 five years from a Dunkirk clay loam soil contained in tanks 

 four feet deep and four feet two inches square. 



Table 24. — Number of Pounds of Plant-Pood Materials 

 Removed in Drainage Water from One Acre of Land 



121. Effect of crop growth on loss of plant nutrients in 

 drainage. — It will be seen that the loss of lime is very large, 

 amounting to several hundred pounds to the acre. The soil 

 with no vegetation has suffered much more in this respect 

 than has the soil that was planted. The soil that was 

 fertilized with sulfate of potash lost somewhat more lime 

 than did the unfertilized soil. The loss of magnesia followed 

 the same course as did the lime. More potash was lost 

 from the unplanted soil than from the cropped, but the use 

 of a potash fertilizer did not increase the removal of potash. 



In the case of nitrogen, the effect of not cropping the soil 



