Jan. is, 1921 



Effect of Crops on Water Extract of Soil 



665 



determinations of total solids. The results of. these conductivity deter- 

 minations are plotted in figures 1 and 2. 



Here we find that all the crops have reduced the concentration of the 

 water extracts during the middle of the growing season. It is interesting 

 to note in the cases of the barley crops that even the smallest number of 

 plants was sufficient to effect a substantial reduction of water-extractable 

 solutes by the time 

 the plants had be- 

 come well establish- 

 ed. The uncropped 

 soil, on the other 

 hand, maintained 

 a remarkably uni- 

 form concentration 

 throughout the per- 

 iod of observation. 



Nitrates were de- 

 termined at a few 

 periods, and these 

 results are given in 

 graphs 3 and 4. 



Here we see that 

 each crop at matur- 



FiG. 3. — Decrease of water-soluble nitrates from the growth of various 

 crops. (Graphs=J£ NO3.) Crops were planted May 13, and soil 

 was sampled on dates given. 



ity had depressed the soil's nitrate content to a minimum, 

 cropped soil constantly remained on a higher level. 



MOVEMENT OF SOLUTES THROUGH THE SOU, 



The un- 



In this experiment two containers of the same soil were placed in the 

 greenhouse and buried in the ground, level with the floor for heat in- 

 sulation. Two* rows of sugar beets were planted across one end of one 

 container. These were spaced 6 inches apart in the row and 9 inches 

 between rows. The remainder of the container, some 40 inches in length, 

 was left bare. Two rows of barley were planted in one end of the other 

 container. The plants were spaced 6 inches apart and 6 inches between 

 rows. This left 40 inches of unoccupied ground. 



The crops were started in December and were allowed to grow until the 

 following March. By that time the beets were about 2 inches in dia- 

 meter and the barley was fully headed. 



Periodic observations of the concentration of the soil solution were 

 made by means of freezing-point determinations. Two samples were 

 always taken from each container, one from between the rows of beets 

 or barley and the other near the bare end of the tank. The freezing- 

 point depressions for both groups of samples are given in figure 5. The 

 last sample in April represents the condition we have previously observed 

 in soils when barley had made about the same growth. 

 17776°— 21 6 



