Experiment station bulletins. 645 



No positive statement can be made on either side of this question be- 

 cause there is no experimental data on record. Arguing theoretically, 

 however, it would seem that the soil receives no heat or only a very 

 unappreciable amount in this manner; first, because the plants them- 

 selves are poor conductors of heat; and second, on account of the fact 

 that there is a tremendous amount of evaporation or transpiration go- 

 ing on from the surface of the plants. Since this evaporation tends to 

 lower the surrounding temperature very markedly, the air temperature 

 around and between the plants may not be very high or but little higher 

 than that of the soil. Nor would it seem likely that in the cold period 

 of the year or during the night the plants would be effective in appre- 

 ciably cooling the soil by mere conduction. 



The difference in temperature between the cultivated, and uncultivated 

 plots is very interesting and needs special notice. This difference in 

 temperature is more complex than it is commonly thought, and our 

 present knowledge and interpretation of it are very incomplete and 

 somewhat faulty. The common belief is that the uncultivated soil is 

 always warmer than the cultivated during the warm part of the year. 

 The reason given for this is that the former soil being a good conductor 

 of heat on account of its compact condition, allows the heat to travel 

 through it faster and to greater depths. This heat during the night 

 recedes from the lower strata to the surface and keeps the upper layers 

 warm, while the cultivated soil, on account of its loose state, is a poor 

 heat propagator, and allows the heat to penetrate downward very slowly 

 and only to a shallow depth. This soil, therefore, during the day will 

 become very hot on the top or upper depth and during the night very 

 cold. 



The results which have been obtained in the last two years do not 

 bear out these beliefs entirely. In the first place, the uncultivated soil 

 is not always warmer than the cultivated during the warm part of the 

 year, but only during certain seasons or times of this part of the year, 

 and under certain conditions; and in the second place, the explanation 

 given for the existing or observed difference in temperature between 

 these two differently managed soils is neither complete, nor entirely 

 correct. 



The results obtained show that immediately after thawing in the 

 spring the average daily temperature of the cultivated soil 7 inches 

 deep, rose gradually above that of the uncultivated and continued to 

 remain in excess until about the middle of May, and then the order 

 was reversed. The average temperature of the cultivated plot for the 

 month of April, in the spring of 1913, was 0.52° F. higher than that 

 of the uncultivated. The records, for the same month for the spring 

 of 1912 are not so complete but those that are available tend to con- 

 firm the above general order. The uncultivated soil absorbed a greater 

 amount of heat during the day time than the cultivated but also lost 

 a correspondingly greater quantity of heat during the night than the 

 latter soil. The gain and loss in heat in the uncultivated soil appears 

 to be more nearly proportional than in the cultivated soil. The average 

 maximum and minimum temperature for the month of April was for 

 the uncultivated soil 47.81° and 41.80° F. and for the cultivated 47.47° 

 and 43.17° F., respectively. The rise of temperature in the cultivated 

 ground was starting in the morning, therefor, at a higher point, some- 



