68 Journal of Agricultural Research voi. xvin. No. 2 



nitrogen absorbed could have been supplied by the nitrate in the soil at 

 germination. The additional quantity necessary was presumably 

 supplied by nitrification. 



The nitrates in the soil approached a very low level at seven weeks and 

 remained low for the rest of the season. We have repeatedly found such a 



MAGNESIUM (Mg) 



vke\i 2 J J 7 S 11 Vi \5 \7 lb* 20 



Fig. 12.— 'Absorption of magnesium by barley, computed to parts per million of soil. 



drop to take place in numerous other cropped soils a few weeks after 

 planting. The greatest rate of absorption by the plant occurred between 

 the seventh and ninth weeks.^ During the succeeding period, ninth to 

 eleventh weeks, the loss of nitrogen from the plant took place. The 

 conjunction of a low nitrate concentration in the soil and high nitrogen 

 content of the plant,^ soon followed by a movement of nitrogen from 

 the plant toward the soil, is difficult to dissociate, although the exact 



Fig. 13. — Absorption of phosphorus by barley, expressed as the phosphate (POi) equivalent and com- 

 puted to parts per million of soil. 



relation is not c^ear. A further and considerable absorption of nitrogen 

 took place between the eleventh and fifteenth weeks. The rate of absorp- 

 tion, however, was never again so great as that of the period between the 



* Nitrates, as such, were fovmd in the plants in decreasing quantities up to nine weeks from planting. 



' Determinations of the various forms of soluble nitrogen in the fresh plant substance at this stage would 

 doubtless give interesting data in connection with the point under discussion here but were not feasible 

 under the conditions of these experiments. 



