72 



Development and Activities of Roots of Crop Plants. 



(at 2 to 2.7 feet), gave the plants a root development quite out of proportion 

 to the tops and markedly different from those of more moist soil. This root 

 development agrees with earlier studies of cereal crops, including winter- 

 grown varieties, and in many respects with that of the native vegetation of 

 the short-grass plains (c/. Weaver, 1920). 



Summary of Environment and Crop Development at All 



Stations, 1920. 



The stations at Lincoln, in southeastern Nebraska, Phillipsburg, in north- 

 central Kansas, and Burlington, in eastern Colorado, are at altitudes of 1,100, 

 1,935, and 4,160 feet respectively. The vegetational expression of the 

 climate at the three stations respectively are true-prairie, mixed-prairie, 

 and short-grass plains. The precipitation for the growing-season, which 

 begins 2 to 4 weeks later at the higher elevation, is shown for each station 

 in figure 32, where the mean precipitation is also included. An examina- 



Fiq. 32. — Mean precipitation in inches (black) and precipitation for 1920 at Lincoln (left), 



Phillipsburg, and Burlington. 



tion of this figure shows that the rainfall at all stations during March was far 

 below normal, but approximately twice normal during April, when the crops 

 were planted. Aside from a deficiency of nearly half the normal rainfall 

 at Lincoln and Phillipsburg during June, and an increase to twice the normal 

 at the latter station during August, no marked irregularities in the pre- 

 cipitation occurred. The total precipitation at Lincoln during the period 

 was 18.8 inches, which was only 0.3 inch greater than that of Phillipsburg. 

 The precipitation at Burlington was about 75 per cent as great, but owing to 

 numerous light showers and great run-off during heavy ones, its actual effi- 

 ciency in increasing water-content of the soil was probably only half as great 

 as the number indicates. 



The soil at the Lincoln station consists of a fine-textured silt loam under- 

 laid with clay loess. At Phillipsburg the mellow silt loam gives way at a 

 depth of about 1 foot to a very mellow loess subsoil. The very compact silt 



