Studies in Prairie and Woodland y 



SOIL MOISTURE 



Soil samples for moisture content determination were taken at 

 stations in the above woodland area and also in the regular sta- 

 tions in the prairie and thicket areas as previously described by 

 Weaver and Thiel. The usual technique was followed in secur- 

 ing these samples, in drying them in electric ovens and in com- 

 puting the percentage of moisture present. The samples were 

 always taken in duplicate, or in triplicate and the average per- 

 centage obtained in this manner was used as the water content for 

 each class. The depth classes were 0-6 in., 6-12 in., 12-24 in., 

 24-36 in., 36-48 in. and 48-60 in. Samples were taken at these 

 depths in all of the stations and at frequent intervals, although 

 the deeper series were taken only at monthly intervals beginning 

 in April and ending in September. Samples were taken at cer- 

 tain depths as often as once a week. Weather conditions fre- 

 quently interrupt any set program for soil sampling routine. 



The salient features of soil moisture conditions at the various 

 depths in the above woodland habitat, in the sumac thicket on the 

 prairie, and in the typical prairie station at Lincoln (the latter 

 two stations previously described by Weaver and Thiel) for the 

 vegetative season of April to September, 191 7, may be readily 

 portrayed by a series of graphs. These graphs indicate at a 

 glance the fluctuations in water content for each depth and sta- 

 tion and also the march of soil moisture for the whole season. 



Figure 3 shows the moisture conditions of the soil at the wood- 

 land station for the 0-6 in., 6-12 in., and 12-24 in. depth classes. 

 The horizontal lines in the figure represent the wilting coef- 

 ficients for the soil at 0-12 in. and 12-24 in-;, the lower line being 

 that for the second foot of soil. It will be noted that the per- 

 centage of moisture in the second foot, of the woodland soil was 

 considerably lower than that in the first foot throughout the sea- 

 son of 1917- Also that the wilting coefficient was reached for 

 only a brief period during the latter part of July and continuing 

 into the fore part of August for the second foot. This period 

 coincides fairly closely with the maturation of the greater num- 

 ber of species whose root systems probably secure water supplies 

 from the upper two feet of soil. The fluctuations of soil moisture 



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