VII. ROOT DEVELOPMENT OF CROP-PLANT ECADS. 



A number of crop plants were grown under two distinctly different sets 

 of environmental conditions near Lincoln, and their root development 

 followed throughout the growing season. The plants experimented 

 with were alfalfa, Medicago sativa; sweet clover, Melilotus alba; brome 

 grass, Bromus inermis; orchard grass, Dactylis glomerata; meadow 

 fescue, Festuca elatior; oats, Avena sativa; sorghum, Andropogon sor- 

 ghum; sunflower, Helianthus annuus; white clover, Trifolium repens; 

 and red clover, Trifolium pratense. They were grown in plats 5 feet 

 square with an uncropped area of 2.5 feet between each plat. The 

 plats, which were in duplicate on each site, were arranged in three rows 

 in a rectangular field. Care was taken to plant the taller crops, such as 

 sunflowers, sorghum, and oats, in such a position as not to shade the 

 adjoining crops. The plats of spring wheat, timothy, and bluegrass 

 were accidentally injured or did poorly and were abandoned (plate 23). 

 All the plats and intervening areas were kept free from weeds. While 

 25 square feet is too small an experimental area for a study of crop pro- 

 duction, it was sufficiently large for root examination, and it is believed 

 that near the center of the plats the roots developed under normal field 

 conditions. Moreover, the space between the plats was ample to pre- 

 vent root competition between crops, at least during the first season's 

 growth, except in the case of the widely spreading roots of sunflowers, 

 where many times this intervening space is necessary. In fact, the 

 adjoining plats of timothy and bluegrass were abandoned because of 

 the severe competition of the sunflower (fig. 37). One of the experi- 

 mental fields was located at the edge of the flood-plain of Salt Creek 

 and adjoining the base-station area of typical low prairie described on 

 page 39. The other was approximately a mile distant and about 80 

 feet higher. It was located on a broad, level hilltop of silt-loam and 

 adjoining the area of typical upland prairie described on page 36. In 

 the two areas the experimental plats were exact duplicates in location 

 within the area, time and amount of seeding, etc. In both areas the 

 soil had been cultivated for many years. In the lower area the crop of 

 the preceding year was potatoes; in the upland it was Sudan grass. 

 The upland seed-bed was prepared by double disking the soil to a depth 

 of 4 or 5 inches on April 23, the lowland by plowing to the same depth 

 at the same time. All of the crops except cane were planted by hand 

 and in measured amounts in each plat on April 24. In every case each 

 crop was sowed at approximately the normal field rate of seeding for 

 eastern Nebraska. An exception to this was the sunflower, one plat of 

 which was seeded very thick and the other much thinner in each area, 

 for the purpose of a study of root competition. At the time of plant- 

 ing, both fields were in excellent tilth, the subsoil was moist (table 19), 



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