Agro-Climatological Investigations— Bensin 207 



ture content of the soil. While soil on the hillside is drying 

 rapidly during the month of June after snow melting in April 

 and early May, soil on the bottomland retains moisture because 

 the snow melting and refrosting of the soil on the flat land is 

 slower. As a matter of fact water stands on the frozen soil until 

 the first part of June. 



During a dry season, like in 1946, temperature on the hillside 

 field at the depth of 6 inches reached 65 °F. on July 10, as shown 

 on Fig. 4. On the bottomland soil temperature movement is 

 much slower even in a warm season as 1950, as shown on Fig. 5. 



During the long warm season of 1949, with a rainy June, the 

 highest soil temperature on both fields was observed in the 

 middle of July, as shown on Fig. 6. 



In most cases soil temperature in the lower levels moves 

 slowly and root movement is limited by the low temperature of 

 the soil. As a result the root system of crop plants is bound to 

 be very shallow which is a quite distinct morphological feature 

 of the regional types of all crop plants including vegetable 

 crops, grains and perennial legumes like alfalfa and clover 

 (Bensin, 1928). This cool soil also has an effect upon the potato, 

 tubers being flat and roots turning toward the south. Pedo- 

 thermal deficiency therefore is among the basic environmental 

 factors of this subarctic permafrost region, limiting agricultural 

 land use and production of several field crops of the temperate 

 zone such as soy beans, corn, sweet potatoes and warm season 

 vegetables such as tomatoes, etc. The problem of warming soil 

 by the proper cultural methods is basic for Alaskan agriculture 

 and horticulture. 



Microclimate Problems and Experiments 



Microclimatogical observations and experiments made by the 

 author in the Tanana valley in 1945-1950 indicate the great 

 significance of the microclimatic factors of the sub-arctic en- 

 vironment for agricultural land use. By clearing land we 

 actually are creating a new microclimate affecting soil tempera- 

 ture and lowering the permafrost table. Topography, location 

 and dimensions of cleared field are among the microclimatic 



