4 FERTILIZING VALUE OF HAIRY VETCH. 



The difference in the quantities of nitrogen furnished by the two 

 lots of field-grown vetch is probably even greater than that shown here, 

 owing to the partial inoculation of the pot-grown vetch plants from 

 which the percentage of nitrogen was obtained. It is not to be con- 

 cluded, however, that 100.51 pounds of nitrogen in one case represents 

 the net gain from growing inoculated vetch, or even that the difference 

 between 100.51 pounds and 28.91 pounds (71.6 pounds) represents 

 exactly the amount of nitrogen abstracted from the air by the root- 

 nodule bacteria. A very considerable part of the nitrogen even in the 

 case of an inoculated plant is derived from the soil. The more vigor- 

 ous the plant and more wide spreading its root system, the greater will 

 be its ability to secure nitrogen from the soil. 



If, however, this 71.6 pounds of nitrogen is counted as clear gain 

 (that is, taken from the store of atmospheric nitrogen) it can not be 

 assumed that this becomes at once available for the succeeding crop. 

 There is reason to believe that the greater portion of it becomes avail- 

 able under favorable conditions within a comparatively short time, but 

 it can not be stated as proved, for instance, that this amount of nitrogen 

 turned under (71.6 pounds) is equivalent to the application of 475 

 pounds of nitrate of soda (15 per cent nitrogen). 



POT EXPERIMENTS WITH TOBACCO. 



To carry the pot experiments still farther the soil in each pot was 

 thoroughly stirred and prepared for setting out tobacco plants. In part 

 of the series the vetch or rye was turned under and in part removed 

 entirely from the pot. The pots were kept moist for four weeks, tap 

 water being used, to allow for the decomposition of the plants turned 

 under. 



Sodium nitrate was chosen as a carrier of nitrogen to compare with 

 that furnished by the plants turned under and was supplied at the rate 

 of 200 pounds to the acre three days before setting out the tobacco plants. 

 To get the maximum effect of this fertilizer some duplicate pots on 

 which no cover crop had been grown were fertilized at the rate of 200 

 and 500 pounds of sodium nitrate to the acre. 



Selected tobacco plants from Connecticut seed, apparently of equal 

 size and vigor, were set out in the pot?, a single plant to a pot. Th^e 

 pots were watered with tap water from this time to the completion of 

 the experiments (April 16 to July 22, 1908). The tobacco did not do 

 especially well under greenhouse conditions, but all plants were affected 

 alike. As all the vetch plants turned under were considerably inocu- . 

 lated when taken up, no separate account was kept of the inoculated 

 and control series. The fertilizer used was 200 pounds of sodium 

 nitrate to the acre. The results, given in terms of the green weights of 

 the plants cut off at the surface of the soil, follow: 



