100 Development and Activities of Roots of Crop Plants. 



of the container. The total water lost at the several depths, both by the 

 sealed and unsealed checks and by the cropped containers, is shown in table 35. 

 Allowing for losses from the surface layer by direct evaporation (as indicated 

 by the checks), the water removed by absorption is quite uniform in amount 

 (about 16 to 18 per cent) to a depth of 2 feet. Below this level it gradually 

 diminished in amount to the maximum depth, but even below 3 feet a large 

 amount of water was removed. The movement of water by capillarity plays 

 a rather unimportant role in replenishing water at the various levels from 

 those adjacent, as may be inferred from the water relations of unsealed con- 

 tainers when compared with those where such movement was prevented by the 

 wax seaL 



Greenhouse Experiments, 1920-21. 



During the fall of 1920 another series of experiments was started in the 

 greenhouse at the University of Nebraska, with the object of determining the 

 depth at which crop plants remove nutrients from the soil. On October 16, 

 44 bags of soil, each weighing about 125 pounds, were secured from the upland 

 experimental plats about 3 miles north of Lincoln (p. 40). The mechanical 

 and chemical analyses of this soil to the depth to which it was removed (4 feet) 

 are given in tables 8 and 9. In securing the samples, two large rectangular 

 trenches were dug and the soil removed from the first, second, third, and fourth 

 foot and bagged separately. 



Twelve large containers were employed for growing the crop. These 

 were the same as those used in the field experiment, except that the smaller 

 ones were enlarged so that all had a depth of 3.5 feet. Five had a diameter 

 of 1.5 feet, while the others were only 1 foot wide. Before filling the containers 

 the soil from each level was spread out on the cement floor of the greenhouse 

 and worked over until all lumps were broken up and the soil thoroughly mixed. 

 Water was slowly added as the mixing proceeded until the water-content was 

 at an optimum, and, after standing for a period, uniformly distributed through- 

 out the soil mass. 



The nutrients used in this set of experiments were limited to nitrates for 

 several reasons. Nitrates, unlike phosphates and potash, are not adsorbed 

 by soil and can be completely recovered by simply leaching with water. 

 Consequently a known quantity could be added to the soil when the con- 

 tainers were filled, and its use by the plant determined by a chemical analysis 

 of. the soil after the containers were opened. Not being adsorbed, they can be 

 expected to diffuse readily throughout the soil along with the movement of 

 water. They are used in comparatively large quantities by such crops as 

 barley, which was employed in this experiment, and hence the error in deter- 

 mining by analysis the percentage used by the plant is reduced to a minimum. 

 Furthermore, the presence or absence of an abundance of nitrates is shown by 

 the foliage of the plant in a striking manner. 



The soil was impregnated with sodium nitrate at the rate of 400 parts per 

 million (i. e., 292 parts per million of N0 3 ) before it was placed in the con- 

 tainers. This was accomplished by weighing the amount of thoroughly 

 pulverized and well-watered soil necessary to fill a container to a depth of 1 

 foot when compacted and adding to this the proper amount of salt in a dry 

 state. The soil was again thoroughly mixed after the salt was added. 



