286 HOW CROPS FEED. 



throughout the period of expermient, but only those 

 amounts that remained at the time of taking the samples. 

 What the vegetation took up from the planted plots, what 

 was washed out of the surface soil by rains, or otherwise 

 removed by chemical change, does not come into the 

 reckoning. 



Those plots, the surface soil of which was most occupied 

 by active roots, would naturally lose the most nitrates by 

 the agency of vegetation; hence, not i;nlikely, the vetch 

 and oat plots contained so little in June. The results up- 

 on the beet, and vacant ground ])lots demonstrate that in 

 that month a rapid formation of nitrates took place. It 

 is not, perhaps, impossible that nitrification also proceeded 

 vigorously in the loose soils in July and August, but was 

 not revealed by the analysis, either because the vegetation 

 took it up or heavy rains washed it out from the surface 

 soil. ■ In the brief account of these experiments at hand, 

 no information is furnished on these j)oints. Since m.oist- 

 ure is essential to nitrification, it is possible that a period 

 of dry weather coming on shortly before the soil was 

 analyzed in July, August, and September, had an influence 

 on the results. It is certainly remarkable that with the ex- 

 ception of the vetch plot, the soil was destitute of nitrates 

 on the 9th of September. This j^lot, at that time, was 

 thickly covered with fallen leaves. 



We observe further that the nature of the crops influ- 

 enced the accumulation of nitrates, whether simply bo- 

 cause of the different amount of absorbent rootlets pro- 

 duced by them and unequally developed at the given 

 period, or for other reasons, we cannot decide.* 



From the third Table may be gatliered some idea of the 

 total quantity of nitrogen that was present in the soil in 



* It is remarkable that the large-leaved beet plant had a great surplus of ni- 

 trates, while the oat plot was comparatively deficient in them. Has this fact any 

 connection with what has been stated (p. 84) regarding the unequal power of 

 plants to provide themselves with nitrogenous food ? 



