92 



THE ROTHAMSTED EXPERIMENTS. 



Potash 

 and total 

 produce. 



Potash in 

 grain and 

 straw. 



ten-yearly periods, and over the forty years. 

 Table (30) gives particulars on these points :- 



TABLE 30. 



The following 



It will be seen that there was almost identically the same 

 amount of produce of grain per acre per annum over the 

 forty years without as with the supply of potash — the aver- 

 age annual deficiency being only f bushel ; and the details 

 show that the falling off was chiefly during the fourth period 

 of ten years. There was, however, some deficiency of straw 

 without potash -supply over each of the four periods. It 

 was considerable over the third and fourth periods, and it 

 amounted to an average of 2 cwt. per acre per annum over 

 the forty years. 



It would appear, therefore, that the diminished amount of 

 potash taken up by the plant where it was not supplied 

 was sufficient for the exigencies of grain-formation for the 

 greater part of the whole period ; and that at least a large 

 proportion of the excess taken up where it was liberally 

 supplied was surplusage so far as the requirements of the 

 grain were concerned. Some idea of how great was the 

 surplusage may be formed by reference to the difference in 

 the amounts of potash eventually remaining in the straw. 

 Thus the average amounts of potash per acre per annum in 

 the straw were — over the first period, without supply 22.5 lb., 

 and with it 39.9 lb., or + 17.4 lb. ; over the second period, 

 without supply 16.4 lb., and with it 48.4 lb., or + 32.0 lb. ; 

 over the third period, without supply 8.0 lb., and with it 

 37.8 lb., or + 29.8 lb. ; over the fourth period, without supply 

 6 lb., and with it 32 lb., or + 26 lb. ; and over the forty years, 

 without supply 13.2 lb., and with it 39.5 lb., or 26.3 lb. per 

 acre per annum more with than without supply. It is not to 



