SUBSOILS CONTAIN PLANT-FOOD ELEMENTS 71 



There are many productive silt loams that do not contain such 

 reserves as here represented. It is well, to be sure, to possess a 

 farm of silt loam having a supply of plant-food elements at least 

 equal to that contained in an average, productive silt loam; or a 

 sandy farm having soil analyzing much better than a poor sand. 

 And it is more encouraging to possess peat that analyzes 0.15 

 per cent phosphorus and 0.5 per cent potassium than it is to have 

 peat containing 0.07 per cent phosphorus and 0.2 per cent potas- 

 sium. The cropping possibilities of a soil are greater when the 

 supply of plant-food elements in it is good. 



Per Cent not the Best Basis for Comparing the Supply of Plant- 

 food Elements in Soils. When we compare the per cent in the 

 table on page 70, we see that average peat contains twelve times 

 the amount of nitrogen contained in a productive silt or clay loam ; 

 but when we compare the amounts in pounds per acre seven inches 

 deep, we find the comparison to be only three times. It is to be 

 further observed that peat shows a higher per cent of phos- 

 phorus than silt loam; but in an acre seven inches deep of peat 

 there are only 600 pounds of phosphorus while in a silt loam there 

 are 2000 pounds. The explanation of this lies in the fact that 

 soils vary a great deal in weight. In round numbers an acre of 

 each of these soils seven inches deep weighs when dry as follows : 



Sand 2,500,000 Ibs. Muck 1,000,000 Ibs. 



Silt loam or clay loam . . . 2,000,000 Ibs. Peat 500,000 Ibs. 



Peat Soils are Deficient in Potassium and Phosphorus. In 



comparing the supply of plant-food elements of soils on the " pounds 

 per acre" basis, we observe that peats are abundantly supplied 

 with nitrogen, but are deficient in potassium and phosphorus 

 (see Chapter IV). We can now fully understand why these soils 

 require mineral fertilizers, viz., potash and phosphates. 



Peat Lands are Sometimes Deceptively Advertised. To him 

 who is unfamiliar with soils, a comparison of the per cents of the 

 plant-food elements contained in them seems a reasonable basis 

 for judging their agricultural values. A drained peat analyzing 

 three per cent nitrogen and 0.1 per cent phosphorus may seem 

 to him as good if not better soil than a prairie loam analyzing 0.26 

 per cent nitrogen and 0.08 per cent phosphorus. Such a compari- 

 son is often used in advertising peat lands. It is well, therefore, 

 to secure full information before investing (Fig. 28). 



Subsoils Contain Plant-food Elements. It is important to 

 bear in mind that subsoils also contain the important elements. 



