SOILS 



1845 



TABLE I 

 CompositiOD of Soil from Typical Fruit Districts in WiisliiiiKton 



These figures show the total supply of 

 these plant toed elements in the soil, de- 

 termined by the otficial methods of soil 

 analysis. There is, of course, no means 

 of determining from these figures just 

 what amounts of plant food will be avail- 

 able during any one growing season, i. e., 



what its "fertility" or productive capac- 

 ity, so far as plant food is concerned, for 

 that particular season or crop will be. 

 However, the standards shown in Table 

 II are often used as a basis for classify- 

 ing soils with reference to their relative 

 "richness" in plant food supplies. 



T.VBLE n 



Practical Ratings of Soils by Plant-Food Percentages According to Professor Kaoker, 



Halle Station, Germany 



Supply of Plant Food 



The above facts are all presented in 

 terms of percentage of the "fine earth" of 

 the soil. i. e., the portion of the soil which 

 is fine enough to serve as a source of 

 plant food supply. If it is desired to 

 know these same facts in terms of pounds 

 per acre of these elements, it is easy to 

 compute this from the weight of soil per 

 acre. For average soils, this is about 

 4.000.000 pounds per acre-foot, i. e., an 

 acre of average soil one foot deep weighs 

 approximately 4.000.000 i)Ounds. A soil 

 carrying 0.417 per cent of potash would 

 therefore have 4.000,000 by .00471. which 

 equals 18.840 pounds of potash in each 

 foot in depth. Computations of plant food 

 supplies are usually made to include only 

 the top foot of soil, as by far the greater 

 proiiortion of the crops food is drawn 



from this part of the soil, chiefly from 

 the tilled portion. 



Availalilc Fertility 



In order that any soil shall produce 

 the maximum crop which the moisture 

 supply and weather conditions will per- 

 mit, enough of the plant food of the soil 

 must become available during the grow- 

 ing season of the crop to build up this 

 maximum crop growth. The process by 

 which unavailable plant food, in the 

 form of mineral particles and partially 

 decayed vegetable matter in the soil, be- 

 comes available to plants is essentially 

 one of decay. Humus, or actively decay- 

 ing vegetable matter, is the chief agent 

 in making plant food soluble, or avail- 

 able. The problem of jiroductivity. from 

 the standpoint of food supply, is there- 

 fore that of keeping the processes of hu- 



