Sails 51 



harvested, are plowed underneath the soil to enrich it. Such 

 a crop is known as a green-manure. (See paragraph 27.) 



Each kind of legume seems to have its own particular kind 

 of bacteria on the roots of the plants. If the right sort of 

 bacteria is not present in the soil, the crop will not receive the 

 benefit of the added available nitrogen, for no bacteria will 

 be found on the roots of the plants to change the free nitrogen. 

 The bacteria multiply so rapidly, however, that a field can 

 easily be inoculated with the proper species of bacteria. This 

 is accomplished, provided tubercules are found on the plants, 

 by spreading, on the land to be inoculated, soil from a field where 

 the same kind of crop has been growing. About five or six 

 bushels of soil to the acre is sufficient, if it is spread thinly 

 and harrowed well into the soil at once. The spreading 

 should be done on a dark cloudy day or after sundown, be- 

 cause sunshine kills bacteria. Pure cultures of bacteria for 

 inoculating the seed of legumes can be obtained from seeds- 

 men and in small quantities from the United States Depart- 

 ment of Agriculture. These cultures are mixed with water 

 and spread over the seed, which is to be planted and, in this 

 way, the bacteria are carried into the soil. 



QUESTIONS 



1. What is soil and of what is it composed? 



2. What are the benefits of humus in the soil ? 



3. Distinguish between residual and cumulose soils. 



4. What is a humid soil, a light soil, a loam, a silty soil ? 



5. Explain the three so-called forms of soil-water. 



6. Tell ways in which the farmer can increase the moisture-con- 

 tent of his soil. 



7. Of what use is a soil mulch ? 



8. Under what conditions is irrigation practicable in humid cli- 

 mates ? 



9. Why is air needed in a soil? 



10. How does a crop of clover benefit the land? 



11. Distinguish between soil texture and soil structure. 



