114 CAMPBELL'S SOIL CULTURE MANUAL 



forming of an almost impervious crust, either on the sur- 

 face or beneath a soil mulch. The most marked effect 

 of this crust was brought out at the Pomeroy model farm, 

 Hill City, Kansas, in 1901, during an extremely long dry 

 period in mid-summer when for nearly three months al- 

 most the entire country experienced one hundred degrees 

 of heat, at times the thermometer running even higher, 

 without any rain. Because of wheat harvesting and other 

 pressing work the orchard was left from fifteen to eighteen 

 days without cultivation. During this time a crust had 

 formed under the mulch which we had kept fully two 

 and a-half inches in depth. The crust was nearly one inch 

 thick and was so dense that the air was almost completely 

 shut out. This crust was caused by the mulch becoming so 

 heated through the direct rays of the sun that the moisture 

 in the firm soil just beneath formed a vapor and passed 

 off through the pores of the mulch, to a degree moistening 

 the mulch, and allowing enough capillary attraction, 

 which together with the heat, permitted much of the 

 moisture to be lost by evaporation. This resulted in 

 bringing up much magnesia, alkali salts, etc., in a soluble or 

 dissolved condition. When this soluble matter reached 

 the point in the firm soil near the surface, where the moist- 

 ure was transformed into vapor by the intense heat, it 

 became a solid, and these minute particles gradually filled 

 up the pores in the top of the firm soil. 



Our attention was first called to this on returning 

 after an absence of four days from the farm, by noting the 

 fact that the foliage of the tree was losing its dark green 

 color. To ascertain the reason for this, after finding that 

 there was ample moisture beneath the crust, the exper- 

 iment of double disking one-half of the orchard was tried. 

 The disk was set to cut as deeply as possible, thus com- 



