E. J. Russell and A. Appleyard 



23 



Rainfall. If instead of taking tlie percentage of moisture, we plot 

 rainfall for the week preceding the date of samjjling, we obtain a 

 somewhat closer relationship with the CO2 curves (Fig. 9). The May 

 maximum (1913) is seen to coincide with a period of high rainfall: the 



Feb. Mar. Apr.May June Jill vAug.Sept. Oct Nov. Dec, Jan. Feb. Mar. Apr. Mayjune July Aug. Sept 



Fig. 8. Curves showing percentage of CO2 in air of Broadbalk unmamired plot 

 and soil moisture to a depth of 9". 



0-8 



0-7 



0-6 



I 0-5 



I 0-4 

 x^ 



<s 



O 0'3 



0-2 



0-1 



0-0 



Feb. Mar.Apr.MavJuneJulyAug..SepLOcL No- Doe, Jan Keb..Mar,Apr.Mav.linieJuly Aug,Sept, 



Fig. 9. Curves showing percentage of CO2 in air of Broadbalk unmanured plot, 

 and rainfall for seven days preceding day of sampling. 



October maximum follows after a second high rainfall and the intervening 

 summer minimum is in a dry period: the April (1914) and the June 

 maxima occur with other high rainfall periods. These are not simple 

 moisture effects, for they are not brought out so clearly on the moisture 

 curve, and we have to seek some other explanation. Two factors appear 



