318 THE TURNIP CROP. 



instances, though not in all, be prevented by the liberal 

 use of lime, which must be applied one or two years pre- 

 viously. We know from our ash analysis that turnips 

 require for their healthy development a large proportion 

 of potash, and if this is not obtainable, their health and 

 growth are proportionably affected; and we also know 

 that heavy and clay soils contain that salt in greater pro- 

 portion than the lighter class of soils, on which the disease 

 is the most frequent and the most severe. The action of 

 lime on clay soils is twofold it acts mechanically, by 

 assisting in their disintegration, and it acts chemically 

 by aiding their decomposition, and thus setting free the 

 potash they may contain in an insoluble state, and conse- 

 quently unavailable to the turnip plant. On the light 

 turnip soils of Norfolk and Suffolk the disease is, however, 

 far less often seen than on the heavier and richer soils of 

 the north. The lime, which is recommended as the remedy 

 here, is of but little value there, as there are no salts of 

 potash locked up in their soil ; but instead of lime, they 

 find an equally effective remedy in marl, 1 which they 

 apply largely to their fields, and thus keep their turnips 

 free from disease. It is generally considered that the dis- 

 ease is more frequently met with now than in former years. 

 if that be the case, it would confirm the suggestion we 

 have advanced, as the great mass of manure now used in 

 their cultivation is bones or " superphosphate," containing 

 phosphates in abundance, but no potash at all, though the 

 plant requires (see p. 328) three times as much of that as 

 it does of the phosphoric acid of the manure. In regard 

 to that form of the disease which is properly termed 

 " anbury," this deficiency of potash would no doubt exert 

 the strongest influence; in the mere "fingers-and-toes" its 

 influence would be less, as this form of disease arises from 



1 Marl is a mixture of lime and clay in differing proportions : the marls of 

 the lower chalk, which are used in the eastern counties, are all rich in potash. 



