114 Bulletin ITtt. 



decaying vegetable matter. Tliis would probably be the condition 

 in the case assumed in the question. 



11. If humus in soil under cultivation is perishable^ ought it not 

 to he the far ine7''^ s first care to keej) good the (juantity first found in 

 the virgin soil f 



Yes; and this can be done only' by adding humus from time to 

 time in the shape of barn-yard manure and other forms of organic 

 matter. 



12. In addition to the hutnus returned to the soil in manure^ 

 from forage fed to stocky and hy plowing under stuhhle and roots ^ 

 do you think it a good plan to sow some cover-crop in corn roivs at 

 last cultivation^ and on oat and wheat stuhhle as soon as the crop is 

 ofi\ for plowing under the following spring f 



Usually a cover-crop is desirable, and especially so if the soil is 

 lacking: in humus. 



13. What are good crops for this purpose f 

 Crimson clover, vetch, peas, rye, rape, barley, oats. 



14. Which of these are leguminous plants f Name all the hinds 

 of leguminous plants you know f 



The first three named. All the clovers, alfalfa, vetch, peas, beans, 

 lupines. 



15. Why is it advised to plow under the green-crops as soon as 

 the land can he worked in the spring f 



These crops, if allowed to grow, would give off into the air much 

 moisture needed by the permanent crop ; and besides this, if left 

 until they had made a large growth, there might not be enough 

 moisture in the soil to cause them to decay. 



16. Do yon think a rotation of crops helps the soil to hear the 

 strain of successive cropping f If so, why f 



Yes : this pi'actice admits of supplying humus by means of cover- 

 crops ; it admits of tillage which sets free plant-food , and as different 

 kinds of plants require different proportions of the various plant-foods 

 a rotation prevents an unequal depletion of plant-food, as might be 

 the case if one kind of crop was grown continuously for a long time. 



17. Are you aware that plant-food exists in the soil in hoth 

 available and unavailable forms, and that when plants have used 

 up most of the available portion we call the soil \oorn out f 



