504 Field Experiments on Root-Crops. 



superphosphate of lime, contained more potash than the German 

 salts on plot No. 5. 20 tons of dung^ is a heavy dressing per 

 acre, and probably more than is enough to meet the requirements 

 of the swede crop on the poorest soil. 



On some land such a heavy dose of dung, I have reason to sa}', 

 might do harm to the roots, or, at any rate, not so much good as a 

 more moderate manuring. On light land, however, like that on 

 which the experiments were tried, no fear need be entertained 

 that root-crops will be injured by too much manure. Still I 

 thought it advisable to ascertain whether so large a dose of dung 

 might have been too much for the roots, and therefore used on 

 plot 2 only half the quantity of dung in conjunction with super- 

 phosphate. 



In field experiments with special manures it is desirable to set 

 aside at least two plots for trying the effects of a full and of a half 

 dressing of good farmyard-manure. By comparing the produce 

 of the unmanured plots with that of the plots dressed Avith a 

 perfect manure like dung, a good idea of the agricultural con- 

 dition of the land under trial may be obtained, the results 

 showing to what extent its productive powers may be readily 

 enhanced by particular manures. 



In previous experiments upon root-crops, I found the applica- 

 tion of pui'ely mineral superphosphates more useful to roots than 

 other more complex artifical manures. This I found especially 

 to be the case when the land had been liberally treated before, 

 and Avas in good heart. On naturally poor soils, or land out of 

 condition, on the other hand, the addition of a moderate pro- 

 portion of ammonia, say 2^ to o per cent., as well as of some 

 common salt (5 to 8 per cent.) to a turnip-manure composed 

 mainly of dissolved bone - material was attended with good 

 success. 



In the experiments before us this has been kept in view. One 

 of the experimental plots, it will be seen, was manured with a 

 purely mineral superphosphate, another Avith a mixture of the 

 same superphosphate and crude potash-salts, and a third Avith 

 mineral superphosphate and salt. 



Trials Avith the crude German salts may be useful as a 

 kind of confirmatory test, but neither their success nor their 

 failure is conclusiA'e. The success may be due to the common 

 salt which they contain, as experience has shoAvn that on light 

 soils a moderate dressing of salt, in some seasons, giA'es 

 a considerable increase. The non-efficacy of the crude potash- 

 salts, on the other hand, does not clearly prove that it is super- 

 fluous to apply potash, for the soil may be in a high state of 

 cultivation, and contain abundant stores of plant food, or it may 



