FEETIL1ZEKS 151 



will barnyard manure improve yellow and sickly plants. 

 Besides acting as a fertilizer, barnyard manure improves 

 the texture of the soil, increases its water-holding ca- 

 pacity, and its decay sets free humic acids which ren- 

 der mineral foods of the soil more available. 



Clovers, cow-peas, and other like legumes, also serve 

 as fertilizers, because they have the power of using the 

 nitrogen of the air in a way that will be explained in a 

 later lesson. These plants store up the nitrogen that 

 they take from the air, and if they are plowed under 

 when mature, they add this nitrogen to the soil, as well 

 as large quantities of humus, which in decaying lib- 

 erates other mineral foods already in the soil. 



The principal commercial nitrogen fertilizers are cot- 

 tonseed meal, nitrate of soda, dried blood and tankage, 

 and refuse from slaughterhouses. Nitrate of soda is 

 the best and quickest acting of all these fertilizers. It 

 dissolves quickly when applied to the soil, and is at 

 once available as food for the plants. High grade 

 nitrate of soda contains 15% nitrogen. Two hundred 

 pounds per acre is a heavy application. 



Phosphoric acid. Phosphoric acid is the one com- 

 pound in our soils soonest likely to be wanting, and the 

 one which in the future it will be most difficult to pro- 

 vide. Undeveloped and shrunken seeds usually indicate 

 shortage of phosphoric acid in the soil. Barnyard ma- 

 nure contains a good percentage of phosphoric acid. 

 Ground bones and phosphate rocks are the commercial 

 sources of this fertilizer. There are great deposits of 

 phosphate rock in Tennessee and the Carolinas, and it 



