n6 TILLAGE— MOVEMENTS OF SOIL WATER [chap. 



to each year the crops on the continuous wheat and 

 wheat after fallow plots for the harvest following the 

 given percolation, we shall obtain the following 

 average results, which show in group I the mean 

 crops following autumns of less than average percola- 

 tion, and in group 2 those following autumns of 

 comparatively high percolation. The percolation is 

 given in inches, the crops in lbs. per acre of total 

 produce, both grain and straw ; and as further evidence 

 of the extent of percolation, the average number of 

 days are given during the four months on which 

 water ran from the tile drain underlying the con- 

 tinuous wheat plot 



Thus the bare fallow which increased the succeeding 

 crop above that given by the continuous wheat plot 

 by nearly 48 per cent, in the seasons when a com- 

 paratively dry autumn succeeded the fallow, increased 

 it by less than 8 per cent, when there was much 

 percolation after the fallow. 



It follows, therefore, that the practice of fallowing 

 land is only an economical one where the annual rain- 

 fall is low and where the land is too strong to admit 

 of free percolation ; it is, however, admirably adapted to 

 the successful cultivation of clay land in dry, hot climates. 



