112 Development and Activities of Roots of Crop Plants. 



The water used by the barley in container 12 was very similar in amount 

 at all depths to which the roots were abundant (2.5 feet) ; that in container 

 13 was less below 2 feet. A comparison of these losses with those from 

 plants unearthed on June 13 (table 40) shows clearly the great activity of 

 the deeper and younger roots during the interval between blossoming and 

 maturity. The loss of nitrates at 2 to 2.5 feet was less from container 12 

 than from container 8, which was excavated on June 13. However, the 

 absorption at 2.5 to 3 feet (186 parts per milUon) shows conclusively the 

 activity of the younger roots. 



Iowa Silver Mine corn was planted on May 4. The cylindrical container, 

 which was 3 feet wide and 5 feet deep, was sunk into the soil in the center 

 of an area which was planted to corn (plate 14 a). The fourth and fifth 

 foot were filled with soil from the 4-foot level from the lower crop plats. 

 This had been impregnated with the usual amount of sodium nitrate, wax 

 seals being placed at depths of 3 and 4 feet. The third foot was filled with 

 impregnated soil from the corresponding level from the lower crop plats 

 and separated by a wax seal from the first and second foot of surface soil, 

 taken from the crop plats where the experiment was conducted. Only a part 

 of the surface was covered by the seal, a circular area about 10 inches in diam- 

 eter in the center of the container being covered by sand only. Two 5-inch 

 funnels, inverted and partially filled with sand and connected with large 

 glass tubes which passed through the wooden roof, afforded means of watering 

 the first and second foot of soil. Three stalks of corn were grown in the hill 

 in the center of the container. The crop developed rapidly, reaching a maxi- 

 mum height of 11.3 feet when the pollen was shedding on July 10 (plate 14 b). 



Growth conditions (discussed on p. 88; cf. also fig. 41) remained favorable 

 during July and the first half of August. Warm weather with abundant 

 rains caused the crop to thrive, the corn in the container being furnished the 

 necessary water, from time to time, through the funnels. In this manner 

 50 hters of water were added to both the first and second foot of soil, while 

 on July 25 the roof and surface seal were removed and 20 liters of water were 

 poured slowly on the soil. This was repeated on August 2, when 12 liters 

 were added. After each watering a mulch of straw covered with sand was 

 put on the surface before the wooden roof was replaced. 



The container was excavated and the contents examined on August 15. 

 At this time the three large stalks were 10.5 to 11.5 feet tall, about 1.2 inches 

 in diameter at a height of 2 feet, and each had a large ear about 10 inches long 

 at a height of 6 feet. The lower leaves were drying and the kernels were 

 well filled and beginning to dent. 



The first 2 feet of soil (from which no samples were taken) were very well 

 occupied by roots and were quite dry, the first foot breaking up into lumps. 

 The roots had penetrated the seal at 2 feet and branched so abundantly in the 

 fertiUzed soil below that they were even more abundant than in the surface 

 soil. Every cubic centimeter of soil seemed well filled with roots. In the 

 fourth foot the roots were very abundant, but somewhat fewer than in the 

 third-foot layer. Below 4 feet the roots were sparse; none extended deeper 

 than 4.5 feet. The cause for the shorter root system (the corn roots outside 

 reached depths of over 5 feet) was undoubtedly due to the rich subsoil. 

 The long, white, unbranched root-ends indicated that growth was not yet 



