IV.] 



VALUE OF BARE FALLOWS 



US 



between. In a humid climate or on a porous soil there 

 is great danger of losing the nitrates formed in the 

 summer by washing out during the autumnal and winter 

 rains, nor is there any advantage gained by storing water 

 where the usual winter rainfall is sufficient to saturate 

 the soil. For this reason, in the Rothamsted experi- 

 ments, the plot growing wheat continuously has given a 

 greater crop per acre per annum than the plot fallowed 

 and sown with wheat in alternate years, though the 

 wheat crop following fallow has always been larger than 

 the crop grown the same year on the unmanured plot 



Of course the average crop on the fallowed ground 

 was twice the above figures, i.e., I7§ bushels of grain and 

 1595 lbs. of straw, but it was only grown every alternate 

 year. 



That the autumnal rainfall is the great factor in 

 determining whether a bare fallow shall be profitable 

 or not to the following crop, may be well seen by a 

 further examination of the results obtained at Rotham- 

 sted on these plots, by comparing the crops with the 

 percolation which took place in the autumn previous. 



The percolation through 60 inches of bare soil for 

 the four months, September to December inclusive, as 

 measured by the drain gauge previously described on 

 p. 78, amounted on the average to 6-45 inches for the 

 31 seasons 1870-1901. If, then, we divide the harvest 

 years into two groups according as the autumnal 

 percolation is above or below the average, and allot 



