173 



Table showing the influence of rapid evaporation upon the temperature 



of the soil. 



In the table above are given the observed differences in temperature 

 of a well drained sandy loam and an adjacent black marsh soil, not 

 well drained, the observations being taken simultaneously and the 

 differences in temperature being due largly to differences in the rate 

 of evaporation in the two cases. 



Influence of thorough preparation of the seed-bed. It follows from 

 what has been said in previous paragraphs, that the practice of 

 thoroughly preparing the seed-bed before sowing or planting must 

 have the eSect of decreasing the capillary rise of cold water from be- 

 low and its loss by evaporation from the soil. This then would tend 

 to concentrate the sun's heat in the seed-bed itself,^ first by lessening its 

 rate of conduction downward, and second by diminishing its loss, by 

 lessening the evaporation. In tbe spring, then, early and thorough 

 preparation of the seed-bed tends to make the seed-bed warmer : it di- 

 minishes the loss of soil moisture ; it increases the formation of ni- 

 trates, thus making the soil richer; it hastens and makes stronger the 

 germination and it enables one or more crops of weeds to be destroyed 

 before the crop is up in the way of cultivation. Hence there is much 

 to gain and little to lose in the thorough preparation of the seed-bed 

 before planting. 



Control by underdraining. When land naturally too wet for tillage 

 early in the spring has been thoroughly underdrained, the soil is 

 brought into fit condition for seeding much earlier than would be pos- 



