HOW LEGUMES TAKE NlTHOGEN 



379 



I <ilur of Nitrogen, Phosphate, and Potash in One Ton of Timothy Compared 

 With One Ton of Clover 



If clover takes from the air as much nitrogen as the crop re- 

 moves, leaving the soil as well supplied as before, we may then sub- 

 tract the cost of nitrogen, in estimating the exhaustive effect on the 

 soil. If the clover is plowed under it adds materially to the nitrogen 

 supply. 



Time of Harvesting Grasses and Legumes. As pointed out 

 before, grasses continue to increase in total dry weight up to the 

 time that the seeds reach the hard dough stage. In general, grasses 

 increase about one-fourth in dry weight after blossoming, while 

 clovers reach maximum weight about time of full bloom. After 

 this legumes decline in total weight, probably due to the loss of 

 leaves. This should be considered in determining the best time to 

 harvest. 



Summing up, we find that legumes have a quite different root 

 system than grasses and at least some of them probably draw more 

 heavily on the subsoil. They differ in composition, legumes being 

 higher in protein. Legumes do not exhaust the soil nitrogen, though 

 they draw more heavily on the potash supply. Legumes reach 

 maximum growth at full bloom, while grasses increase one-fourth 

 after this period. 



HOW LEGUMES TAKE NITROGEN FROM AIR 



During the Eoman period it was known that legumes were 

 beneficial to the soil. Jethro Tull, a prominent English agricul- 

 turist, made frequent references to the value of legumes as soil 

 improvers in his writings, 1700-1725. Certain facts about clover 



