Mar. lo, 1919 Organic Matter and Water-Holding Capacity of Soil 269 



The uniformity in texture of both the surface soil and subsoil from 

 plot to plot makes the field unusually favorable for such a moisture study. 

 The thickness of the silt loam layer overlying the gravel stratum men- 

 tioned above varies from about 39 to 50 inches, in nearly all places it 

 being less than 48 inches, and the variations from place to place on the 

 same plots appear as great as those from one plot to another. While we 

 regularly sampled the fourth-foot section along with the second and 

 third, it showed such an extreme range in texture, ov/ing to the varying 

 proportions of its two component layers, silt loam and gravel, that the 

 data on this level are of no use in the present discussion. 



WEATHER CONDITIONS 



The weather of the crop season of 191 5 was favorable for the mainte- 

 nance of a very moist soil, being abnormally rainy, cool, and cloudy (Table 

 IV). In each of the first three months. May, June, and July, the precipi- 



I 5 10 15 20 25 15 10 IS 20 25 15 10 IS 20 25 t 5 10 15 £0 25 



Fig. 2.— Diagram showing the amount and distribution of the rainfall at University Farm, St. Paul, Minn., 

 during part of the season of 1915. The dates of sampling are indicated by asterisks. 



tation was somewhat above the normal and in August it was just equal 

 to the normal. For each of the months the mean temperatures varied 

 from 6.1 to 4.2 degrees below normal and the percentage of possible 

 sunshine in the first three months varied from i6 to 26 below normal, 

 while the wind movement was slightly below and the relative humidity 

 slightly above normal. 



The precipitation of the autumn of 191 4 and the following winter and 

 first two months of spring had been nearly normal, that of April being 

 2.31 inches. The rainfall of the four months covered by the study came 

 chiefly in the form of slow rains which caused but little run-off; excep- 

 tions were provided by two heavy rains, one on July 6 and the other on 

 July 14 (Table V and fig. 2). The dates of sampling happened to be such 

 as to well illustrate the various conditions met with in a wet season. Thus 

 on both July 7 and 15, the samples were taken only a day after a very 

 heavy rain had fallen while on May 18 and August 4 they were taken one 

 day after the last rain in a succession of days with moderate rains. 



