EFFECT OF FAI.l.oWINd 63 



the produce of wheat after fallow is consi(leral)ly hi^lKM* than 

 when it is grown continuously, 171 against 1*J7 l>iishols per 

 acre ; but if reckoned as produce over the whole area, lialfin ciMip 

 and half fallow, the whole acre grows nuich less huth of grain and 

 straw than where the crop is grown year after year on the same 

 land. A given area of land would therefore be more productive 

 when cropped every year than if the crop were alternated with 

 fallow. The superior yield t)f the portion in crop after a 

 ffiUowing may to some degree be attributed to the greater 

 freedom from weeds, but in the main it is due to the production 

 of nitrates from the humus of the soil during the sunnner when 

 it is fallow, a process which is much stimulated by the stirring 

 and aeration the soil receives. The success of a fallowing 

 depends upon these nitrates remaining for the succeeding croj), 

 since they are not retained by the soil they may be entirely 

 washed out by heavy autumnal rains. 



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 comparing the crops yielded by 

 these plots with the rainfall and percolation which took jjlace 

 during the autumn previous to each crop. 



The percolation through GO inches of bare soil for the four 

 months September to December inclusive, as measured by the 

 drain gauge, amounted on the average to 6 ■•45 inches for the 

 seasons 1870-1901. If, then, we divide the years into tw<. 

 groups according as the autunmal percolation is al)ove or l»el(»w 

 the average, and allot to each year the crops on the continut»us 

 wheat and wheat after fallow plots for the harvest following 

 the given percolation, we shall obtain the average results shown 

 in Taljle XXV. and illustrated in the diagram Fig. 1>. 



Taking the seasons of small rainfall, averaging .s-88 inclies 

 f(jr the four months September to December inclusive, the 

 percolation was only 4 inclies, and the total {»n.diut' on the 

 wheat after fallow plot was -27 \V> U*. as against 1^10 11>. nn 

 the continuous wheat plot, or a gain of O:?:! 11«. dn-- to 

 fallowing. 



