142 Commercial Gardening 



tillage operations. If the soil is not cultivated, these foods remain dor- 

 mant, inactive, and insoluble, and therefore worthless to any crop. 



Having 97 per cent of the bulk of his crop practically provided free 

 of charge, except for labour, the cultivator has to devote his energies to 

 supplying the other 3 per cent, made up of nitrogen, phosphoric acid, 

 potash, and lime. Now, the soil is by no means deficient in these foods. 

 In the Broadbalk Field, Rothamsted, it has been found that a soil which 

 had been cropped, but had not been inanured for fifty years, still contained 

 2500 Ib. of nitrogen, 2750 Ib. of phosphoric acid, 6750 Ib. of potash, and 

 62,250 Ib. of lime to the acre at a depth of only 9 in. 



These figures are remarkable, and cultivators would do well to re- 

 member them. If a soil that has been cropped, but has been unmanured 

 for fifty years, still contains such large quantities of the most important 

 plant foods, it ought to follow as a matter of course that a soil which 

 has been cropped and has also been manured for the same period should 

 show far larger quantities of these particular foods. Such, however, 

 is not the case, as the experiments carried out at Rothamsted prove. 

 The addition of certain manures often has the effect of liberating too 



o 



freely some of the plant foods, and as they cannot be absorbed by the 

 crop, they are lost in some way, or at least cannot be accounted for (see 

 p. 128). 



To appreciate all the factors in the case it is necessary to remember 

 what has been already emphasized, that only very small quantities of 

 nitrogen, phosphoric acid, potash, and lime are taken from the soil. It 

 has been estimated that fruit trees and ordinary farm crops take from 

 the soil from 50 to 100 Ib. of nitrogen, 20 to 50 Ib. of phosphates, 30 to 

 150 Ib. of potash, and 150 to 200 Ib. of lime. Comparing the figures with 

 the supplies still remaining in the Broadbalk Field at Rothamsted after 

 fifty years, and with the supplies that are said to be in a fertile soil, it 

 is evident that only small quantities are liberated as food for each crop. 

 The usual deduction made is, that as these supplies of nitrogen, phosphates, 

 potash, and lime are to be found in a soil after fifty years, therefore they 

 are regarded as unavailable and probably useless. This view seems to be 

 quite erroneous. Why should these vast supplies become immediately 

 soluble? Would it not be a dire calamity if they were to become so, and 

 if they vanished in one season? The result would be complete and abso- 

 lute sterility, and succeeding crops would have to starve. Apart from this, 

 it would be a physical impossibility for any crop to take up or absorb 

 62,250 Ib. of lime, 6750 Ib. of potash, 2750 Ib. of phosphates, and 2500 Ib. 

 of nitrogen altogether, 74,250 Ib. (over 33 tons) per acre. In a Turnip 

 crop weighing 33 tons, only about 2 or 3 per cent of the dry weight, say 

 from 1400 to 2000 Ib. would come from the soil, the remainder coming 

 mostly from the air and water. 



In the Bulletin (No. 103) of the Cornell University, U.S.A., for October, 

 1895, the following interesting figures appear in connection with an experi- 

 ment on some Wagner Apple trees thirty-five to the acre. 



