AGRICULTURAL SOILS 93 



used to fertilize plants. But soluble compounds of nitro- 

 gen are not abundant, and these would be soon removed 

 from many soils unless in some way replaced. 



This is most often done by adding manures to the soil. 

 In these there are nitrogen compounds which the bacteria 

 of the soil work over and get into shape so that the plants 

 can use them. Some bacteria are even able to take the 

 nitrogen from the soil-air and combine it so that it can be 



LUMPY SOIL. 

 The result of cultivating at the wrong time. 



used by the plants. If this varied and teeming life of the 

 soil is to thrive, certain conditions must be maintained, 

 and it is the skill of the agriculturist in maintaining and 

 increasing these favorable conditions which determines his 

 success or failure. 



45. Agricultural Soils. As has already been shown, soils 

 differ greatly in fineness, mineral composition and water- 

 holding capacity. They also differ greatly in the amount 

 of decayed vegetable material or humus in them. The 

 humus is a most important soil ingredient. It helps in 



