86 The Control of the Soil [pt. ii 



Fortunately the remedy in both cases is simple : the 

 ground should be rolled during dry weather in spring 

 until the proper degree of compactness is reached. This 

 operation is very necessary on chalk soils, sandy loams, 

 and grass land. 



Rolling is also necessary for corn crops on heavy land 

 in spring to break the crust formed after a spell of wet 

 weather. Great judgment is needed to decide whether 

 rolling or harrow ing is the better operation to perform : 

 a mistake in either direction may cause much harm. 



Summer cultivation consists in hoeing and its object 

 is two-fold : to keep the surface of the soil in a fine state 

 and to kill weeds. A layer or "mulch" of fine soil keeps 

 the land cool during hot weather and prevents loss of 

 moisture. This was shown thirty years ago by the 

 American investigators, Kedzie of Michigan and King 

 of Wisconsin^, and is demonstrated by the following 

 experiment : 



Set out three plots each 3 ft. x 3 ft. : leave one alone 

 entirely so that it may cover itself with weeds : keep the 

 second clean bv hand weeding but do not touch it other- 

 wise: keep the third well hoed. Take readings of the 

 temperature of the soil at depths of \ inch, 3 inches and 

 6 inches below the surface : in particular obtain readings 

 on hot sunny days and on cold sunless days. Periodically 

 also take samples for the determination of the moisture 

 content: this is done by driving in the borer (Fig. 41, 

 p. 227) to a depth of 6 inches, weighing the soil that is 

 Avithdrawn (or a fair sample of it), leaving to dry in a 

 warm place and then weighing again. Table II gives 

 some of the results which have been obtained. 



^ See Kedzie, in Michigan Agric. Coll. Rpt. 1889, and F. H. King, 

 Wisconsin Agric. Expt. Station Rpt. 1889. 



