Investigations at Burlington, Colorado. 



65 



level plat, so that a variation of 1 or 2 per cent of moisture was not uncommon. 

 This variation probably accounts for the water-content apparently being 

 exhausted below the hygroscopic coefficient. It seems, however, that crop 

 plants growing in these more arid soils have a greater ability to more thor- 

 oughly exhaust the water-supply than when grown in more humid regions. 

 This is due possibly to the development of greater osmotic pressure, and cer- 

 tainly to a more thorough occupancy of the soil area by roots. The latter 

 establishes a closer relation to all available soil-moisture, an exceedingly 

 important condition at a time when the soil becomes so dry that all capillary 

 movement of water ceases. 



The soil-temperatures during the period were high. The average daily 

 temperature ranged from 65° (minimum 57°) to 76° F. (maximum 85 F, 

 fig. 28). The average daily temperatures of the surface 6 inches of soil were 



August 



June 



July 



so 



70 



60 



50 



























s \ 





















/-I 



/ 



/ 



/ 



s \ 

 s \ 











































Fig. 28— Average day and average night air-temperatures and average 

 daily soil-temperature (broken line), Burlington, 1920. 



4° to 7° F. higher after the first week of July than those at Lincoln. This was 

 undoubtedly due to the drier and more insolated soil, for at Lincoln both day 

 and night temperatures of the air averaged higher than those at Burlington. 

 At Burlington the air-temperature ranged from 67° to 84° F. by day (maxi- 

 mum 99° F.) and 51° to 60° F. (minimum 43° F.) by night. Soil-tempera- 

 tures at depths of 1 to 4 feet were about the same at both stations. Owing 

 to the lag of soil-temperature (at 6 inches depth) at all stations, both m reach- 

 ing a maximum (about 6 p. m.) and a minimum (about 7 a. m.), the day and 

 night averages at any station were very nearly the same. The great range of 

 air-temperatures from day to night (usually 35° to 45° F.) is significant, for 

 high daily temperatures coupled with low humidity accentuate drought con- 

 ditions, causing partial wilting and cessation of photosynthesis and growth. 

 However, at night conditions are reversed and plants usually have oppor- 

 tunity to readjust their water-equilibrium. In fact, the average nightly 

 humidity (79 to 90 per cent), which is caused largely by the low temperature, 

 was greater than that at Lincoln. However, the average daily air-moisture 

 (39 to 53 per cent) was much less (fig. 29). Not infrequently the hygro- 

 graph registered as low as 17 to 25 per cent. 



It should be pointed out that the season of 1920 was one unusually favor- 

 able for crop development. On several occasions fogs were noted which did 

 not clear away until the middle of the forenoon. Such atmospheric con- 



