484 ANNUAL REPORT OF THE Off. Doc. 



the organisms are present in the soil there is but little danger 

 that they will be destroyed under good conditions of practice, and 

 if the crops that are grown upon the area which has been inoculated 

 are used as food for farm stock and the manure used elsewhere 

 upon the farm the chances are that the organisms will be generally 

 distributed, so that the work of inoculation is not a serious matter. 



It very often happens that in the growing of such crops as cow 

 peas and soy beans the first crop grown will not show the tubercles 

 on the roots, but that the second one grown will b§ well supplied 

 with them, indicating that the organisms are very often introduced 

 into the soil by means of the seed, and seedsmen in some cases now 

 make it a practice in harvesting their crops of soy beans and cow 

 peas to pull them instead of cutting them, thus in threshing, ming- 

 ling more or less of the soil which contains the proper organisms 

 with the seed and which when removed leave the seed well inocu- 

 lated. 



The Amount of Nitrogen Gathered. 



It does not follow, however, that even when these organisms are 

 not present in the soil that all of the nitrogen contained in the crop 

 of the legume grown has been gathered from the air, as it has been 

 shown that the plants would preferably take soil nitrogen, and, 

 therefore, that on good soils, well supplied with nitrogen, the propor- 

 tionate amount of nitrogen drawn from the air will be much less 

 than that will be the case when the crop is grown on soils poor in 

 nitrogen. The exact amount of nitrogen gathered by a crop can- 

 not, therefore, be exactly determined, though it is believed to de- 

 pend upon the character of the soil, whether rich or poor in available 

 nitrogen, hence the usefulness of the legumes as a means of acquir- 

 ing nitrogen is greater when grown upon soils poor in this sub- 

 stance; these soils are, however, more greatly benefited by the 

 accumulation than those previously rich in the element nitrogen. 



The Importance of an Abundance of the Mineral Elements. 



It has also been prettj^ clearly demonstrated that the proportion 

 of nitrogen gathered by the plant from tlie air, particularly upon 

 poor soils will depend upon the supply in the soil of the other neces- 

 sary plant food ingredients. That is, soils poor in nitrogen and 

 oftentimes poor in physical character if not well supplied with the 

 minerals, phosphoric acid and potash, will not produce a large crop 

 of cow peas or soy beans, or any other leguminous plant, because its 

 grows and development depends upon the ease with which it may 

 acquire the necessary amounts of the other elements of nutrition. 

 Hence, in attempts to build up poor soils by means of green manure 

 crops it is quite as necessary to fertilize with the minerals, in order 



