CHAPTER XLI 

 LEGUMES 



BY PROF. A. D. McNAIR, U. S. Department of Agriculture. 



428. Importance of Legumes. We have already 

 learned (If 125) of the association of legumes and certain 

 bacteria, that have the power of converting the free 

 nitrogen of the atmosphere into compounds usable by 

 their host plants. While the bacteria in the nodules on 

 the roots in some way gather the free nitrogen of the air, 

 yet it is not retained by them, but enriches the entire 

 host plant (If 124-130). For this reason they are called 

 "nitrogen gatherers." When properly used, legumes are 

 true soil builders. 



429. Formation of Tubercles and the Accumulation 

 of Nitrogen. All species of legumes form tubercles on 

 their roots, when the proper bacillus is present. In soils 

 rich in soluble nitrates the number of tubercles is often 

 small, while in soils deficient in nitrates, the number is 

 usually greater. Legumes that have tubercles on their 

 roots grow more vigorously and are richer in nitrogen 

 than those that do not have tubercles. From this it is 

 inferred that leguminous plants acquire the free nitrogen 

 of the air when compelled to do so, but when the soil 

 contains an abundance of nitrates, they utilize a larger 

 proportion of the nitrogen salts in the soil. 



430. Soils and Fertilizers for Legumes. Alfalfa, the 

 true clovers, beans, peanuts, and field peas are benefited 

 by free lime and rarely thrive in acid soils. (See tests in 

 If 141). Cowpeas do not require so much free lime, and 

 the same is probably true of soy beans and lespedeza. 



(300) 



