102 



SOILS AND FERTILIZERS 



inorganic matter that remains is either used directly by plants 

 or is absorbed in the same way as the soluble fertilizers. 



In an experiment several organic substances were mixed 

 with soil, the quantities of phosphoric acid and potash com- 

 bined with organic matter being determined before mix- 

 ing and after standing for a year or more. The results of 

 some of these experiments are given in the following table : 



Table 23. — Combinations op Phosphoric Acid and Potash 

 with Organic Matter Produced by Mixing Organic 

 Matter with Soil 



Experiment with cow manure and soil 



In original manure and soil . 



In mixture after standing .... 



Gain in organic form 



Experiment with green clover 



In original soil and clover .... 



In mixture after standing .... 



Gain in organic form 



Experiment with meat scrap 



In original soil and meat scrap . . 



In mixture after standing .... 



Gain in organic form 



Phosphoric 

 Acid Grams 



1.17 

 1.62 



0.45 



3.21 

 3.74 

 0.53 loss 



1.07 

 1.18 

 0.11 



Potash 

 Grams 



1.06 

 1.27 

 0.21 



5.26 

 4.93 

 0.33 



0.25 

 0.36 

 0.11 



When the organic compounds thus formed undergo further 

 decay the inorganic plant-food materials become available. 



119. Loss of plant-food material in drainage water. — 

 The drainage water from cultivated fields in humid regions, 

 and to a less extent in semi-arid and arid regions, except 

 where irrigation is practiced, carries off very considerable 

 quantities of plant-food material. When it is considered 

 that soil is constantly subjected to leaching by rainwater 

 passing through it, that this amounts to many tons of water 

 in the course of a year on every acre of land, and that a water 

 extract of soil always contains some of each of the substances 



