GREEN MANURES 385 



lie bare. Deep-rooted crops usually accumulate a large 

 amount of nutriment from the soil, and considerable 

 from the lower depths. They are therefore useful in 

 bringing plant-food to the upper layer of soil. Succulent 

 crops decompose easily, and dry out the soil less, when 

 plowed under, than do woody crops. Crops with exten- 

 sive root-systems prevent loss of soluble matter more 

 thoroughly than do plants with small roots. 



255. Leguminous crops. A soil that has become less 

 productive under cultivation, and that must be improved 

 before profitable crops can be grown, receives more 

 benefit from the use of leguminous crops than any 

 other. The legume to use is naturally the one best 

 adapted to the region in which the soil is located. Red 

 clover, mammoth clover and field peas on the soils to 

 which they are adapted in the northern states; alsike 

 clover in the wet soils of that region; cowpeas and crim- 

 son clover in the South, and alfalfa, clovers, soy beans 

 and cow peas in the West, are the principal leguminous 

 green-manuring crops. More recently a positive effort 

 has been made in certain northern states to grow sweet 

 clover (Melilotus alba), which is a vigorous wild legume, 

 as a green manure crop. Marked success has followed 

 its use, but, like alfalfa and the clovers, it requires a soil 

 well stocked with lime. 



The legumes have the important property of securing 

 nitrogen from the air, which is added to the soil from 

 the decomposition of the tops and roots when the crop 

 is plowed under. The nitrogen contained in a ton of the 

 green crop, when in a condition to plow under, is as 

 follows: 



