54 AGRICULTURE FOR COMMON SCHOOLS 



in the ground. The effect of manuring can be seen on the 

 yields of crops for many years after the manure has been 

 applied. At the Indiana Experiment Station it has been 

 shown that the manure was making an increased yield twenty 

 years after it was applied. 



Green Manuring. — By green manuring is meant the plow- 

 ing under of green plants so that in their decay under ground 

 they will add humus to the soil. Furthermore, the acids pro- 

 duced by their decay attack the rock particles and make new 

 compounds, some of which are useful as food for plants. The 

 addition of humus, as we have learned, aids the soil in re- 

 taining moisture in a better way and at the same time puts the 

 soil into better condition for cultivation. Sandy soils are 

 made cooler and clay soils warmer by the addition of humus. 



Any kind of plant can be used for a green manuring crop. 

 It is better to plow under weeds while they are green than to 

 let them go to seed. Rye is a common green manuring crop. 

 It is sown in the autumn and plowed under in. the spring. 

 The best green manuring plants are the legumes, because they 

 add nitrogen, and nitrogen is the thing that most soils need. 

 Clovers, cow-peas, soy beans and vetches are all good. Clov- 

 ers do the soil most good if turned under in full blossom, the 

 others when the pods are about one-half grown. Legumes 

 are called nitrogen-gatherers, because they increase the total 

 amount of nitrogen in the soil. All other plants used as green 

 manures can give the soil only the nitrogen which they have 

 obtained from the soil in the first place. 



Usually it is better to cut the clover or cow-peas for hay and 

 feed them and return the manure to the land. By so doing 

 the farmer gets the benefit of the feed for his animals and 

 nearly all the plant food goes back to the land to make it richer. 



