112 



enough over the surface a yellow cast becomes apparent, 

 then a brown, and finally it dies. This is because of a 

 lack of air at the roots. 



The great store house of nitrogen is the atmosphere. It 

 is the place where all is kept that is not in use otherwise. And 

 nitrogen is one of the essentials of plant life. The plants 

 do not take their nitrogen directly from the air; but it 

 comes to the plant in an indirect manner through organic 

 substances in the soil. The nitrogen of the air combines 

 with mineral substances in the soil, and then by reason of 

 the action of bacteria certain compounds are formed 

 which contain nitrogen in a soluble form. Then it be- 

 comes plant food. 



NITROGEN AS PLANT FOOD. 



But you cannot have these compounds containing 

 nitrogen if the other elements are shut off from contact 

 with nature's great storehouse of nitrogen. Hence the 

 circulation of air in the soil is an absolute necessity. Soil 

 in a perfect vacuum is dead soil, and can no more become 

 or develop plant food than soil submerged in water or soil 

 baked to absolute dry ness. 



The great danger in handling soil in relation to the aii 

 in the same lies in the possibility of having a condition 

 that will shut out the air without the farmer knowing it. 

 A heavy rain may produce this undesirable condition. 

 In cut No. 11 is shown what frequently happens and how 

 it may be overcome. It shows soil where there has been 

 a heavy rainfall, beating down the surface which has been 

 softened by the raindrops, and with the result that the 

 upper surface is compacted perfectly. As soon as tho 

 small amount of water near the surface has disappeared 

 by evaporation the upper crust is hard. It is iiripenetra,- 



