114 Development and Activities of Roots of Crop Plants. 



Wheat-grass roots were very abundant to the bottom of the container 

 (depth 2.5 feet) where they were slightly massed. They penetrated thor- 

 oughly all portions of the soil, but were especially well branched in the fer- 

 tilized layers below the first foot. The roots of the big bluestem were also 

 splendidly developed and especially abundant in the second foot. They 

 had not filled the third foot of soil so completely as the wheat-grass. Water 

 and nitrate absorption by the grasses is given in table 43. 



The amount of water used by the grasses is rather remarkable when the 

 brief period of growth is taken into consideration. However, studies of the 

 life-history of grasses (Clements and Weaver, 1921) impress one with the 

 rapidity of root development. The removal of nitrates is also very marked, 

 exceeding considerably in amount that removed by any crop plants used in 

 these experiments. 



SUMMAKY. 



The great depth to which the roots of both native and crop plants penetrate 

 has led the writers to perform a series of experiments to determine the 

 amount of water and nutrients absorbed from the deeper soils. In these 

 experiments containers 1.5 to 3 feet in diameter and 2.5 to 5 feet deep were 

 employed. They were placed in trenches, which were then refilled with soil 

 and crops planted around the containers in such a manner that the experi- 

 mental crops in the containers were grown under field conditions. The con- 

 tainers were filled with well-mixed soil of known water-content and physical 

 and chemical composition, to which, at certain levels, NaN0 3 had been added 

 at the rate of 400 parts per million. The containers were filled in such a 

 manner that the well-compacted soil at any level occupied the same relative 

 position as regards depth that it had occupied before removal from the field. 

 The fertilized layers, and in some cases every 6-inch layer, were separated 

 from the rest of the soil by wax seals which prevented the movement of water 

 or solutes, but through which the roots readily penetrated. To prevent water 

 intake each container was furnished with an appropriate wooden roof. The 

 experiments extended over a period of 2 years, during which time the following 

 crops were grown: oats, barley, potatoes, corn, and two native grasses (Agro- 

 pyrum glaucum and Andropogon furcatus). In order to study the activities 

 of the roots at various stages in their development, enough containers were 

 used (about 50 in all) so that some could be examined at each of the several 

 periods of growth of the crops. 



Preliminary experiments with oats showed that this crop absorbed water at 

 all depths to 2.5 feet, even before blossoming. The amount of water absorbed 

 by barley from the deeper soils (to 3.5 feet) is in direct relation to the growth 

 of the root system into these deeper layers. The total amounts absorbed to 

 depths of 2.5 feet were in general practically the same from the several 6-inch 

 levels. Corn is an extravagant user of water, absorbing large quantities from 

 the third and fourth foot of soil and smaller amounts from the fifth foot. 

 Potatoes absorbed water to depths of 2.5 feet (approximately the limit of 

 root extent), while the native grasses, grown from transplanted sods, showed 

 marked absorption to a similar depth. 



Barley at the age of 54 days had removed 168 and 145 parts per million of 

 nitrates from the 1 to 1.5 and 1.5 to 2 foot soil-levels respectively. When in 



