ROTATION OF CROPS. 231 



The Amounts of Total Mineral Matter (Ash) in the 

 Rotation, and in the Continuous Crops. 



The results are given in Table 62 (p. 232) for each of the 

 four descriptions of crop, in exactly the same form as those 

 for the total dry matter and the nitrogen, in Tables 60 and 

 61 respectively. 



The record is deserving of careful study, as showing the 

 very various, and sometimes very large, amounts of mineral 

 or ash-constituents taken up from the soil, and stored up in 

 the different crops, or parts of the crops. But it must suffice 

 here to direct attention to some of the points of chief interest 

 brought to view, on the consideration of the amount, and of 

 the distribution, of some of the more important individual 

 mineral constituents in the respective crops ; and for the 

 purposes of such an illustration reference will chiefly be 

 made to the amounts of phosphoric acid, and of potash, but 

 in some cases to that of lime also, in the crops. 



The Amounts of Phosphoric Acid in the Rotation, and in 

 the Continuous Crops. 



Table 63 (p. 233) records the results relating to the 

 amounts of phosphoric acid in the different crops or parts 

 of crops. 



The Phosphoric Acid in the Boot-crops. — The figures show No man- 

 that, without manure, the rotation turnip crops took up an ure ' 

 extremely small amount of phosphoric acid, reaching in only 

 one case to an average of 1J lb. per acre per annum. By with 

 superphosphate alone the amount was increased to an average s ^ a ^f ho ' 

 of about 10 lb. ; and although this increase only represents 

 about one-tenth of the phosphoric acid applied in manure 

 it is very important, as it is directly connected with the 

 greatly increased development of fibrous feeding root within 

 the soil, which is a special effect of phosphatic manures 

 when applied to turnips ; and it is by virtue of this develop- 

 ment that these crops so markedly exhaust the available 

 nitrogen within the soil, and especially the surface-soil. As 

 has been shown, there is abundant evidence that the increased 

 amount of nitrogen taken up under the influence of phosphates 

 unaccompanied by any supply of nitrogen itself, is at the ex- 

 pense of the stores of the soil ; and that it is not due to a 

 capacity to take up either combined or free nitrogen from 

 the atmosphere, by virtue of an increased development of 

 leaf-surface, under the influence of the phosphatic manure. 



With the mixed manure, supplying, besides superphos- Mixed 

 phate, salts of potash, soda, and magnesia, and a liberal manure - 



