11J8 EXPERIMENT STATION RECORD. 



(1) A soil covered with living trees or leafy plants is generally cooler 

 in summer and warmer in winter than one not so covered. The great- 

 est difif'erence in temx^erature occurs in summer, is less in spring and 

 autumn, and may entirely disappear in winter; /. e., with rising tem- 

 perature the ditt'erence is considerable, while with falling temperature 

 it is less nuirked. The differences are also greater with forest plants 

 than with agricultural plants. In case of both forest and field jjlauts 

 the soil temperature is iufluenced by the stand, the rate of develoj)- 

 nuMit of the above-ground organs, and the habits of growth of differ, 

 ent species. The thicker the stand and the more vigorous the above- 

 ground growth the greater the effect on the temperature. The heavier 

 the covering of litter the greater the influence on the temperature. The 

 variations of temperature are decidedly lessened by a i)lant cover, 

 and this intiueuce is increased by the presence of a covering of litter. 

 The difference in temperature between covered and bare land is most 

 marked at the periods of nuiximum and minimum daily temperature. 

 The difference between morning and evening temperature is greater on 

 bare soil than on covered soil. 



(-J) A soil covered with growing plants contains less moisture than a 

 bare soil. Cultivation is generally of the highest value in summer, but 

 is of less value in spring and fall. As in the case of temperature, 

 the soil moisture is dependent upon the stanci and rate of growth of the 

 Ijlants with which it is covered. A soil having a covering of litter in 

 addition to that of trees generally contains more moisture than that 

 bearing trees only, but it was observed that the influence of the cover 

 of litter might be lessened by the increased growth of trees in this 

 case drawing a larger amount of water from the soil. In fact in the 

 later stages of growth the decomposition of the litter furnishes material 

 for such a vigorous growth that the influence of the cover of litter on 

 the moisture content of the soil is entirely overcome. 



(3) Drainage is less from covered than from bare soils. The differ- 

 ence is greatest in summer, and decreases steadily until the following 

 spring. Drainage is greater with evergreens (pines) than with folia- 

 ceous trees (birches) and grasses. A covering of litter retards the 

 sinking of the water into the lower layers of the soil. In bare soils the 

 drainage generally increases and decreases with the rainfall, and there- 

 fore in regions of summer rain the most abundant drainage would be 

 observed in summer. Under such conditions, however, relatively the 

 smallest amount of water would be carried down in the drainage in 

 summer, the greatest in the cold season. On covered soil as compared 

 with fallow soil the minimum amount of drainage is in summer and 

 increases until the following spring. 



In soils covered with plants the relation between drainage and rainfall 

 is qualitatively the same at difl'erent seasons of the year as in bare soils. 



In the mild winters of 1889-'90, 18{)l-'92, and 1892-'93 the greatest 

 fimount of drainage occurred at this season, while in all cases where 



