ROOT-CROPS. 51 



of nitrogenous manures in some cases more than quadrupled 

 the produce. Thus the average produce of plots 6 and 4, 

 with potash as well as superphosphate as the mineral manure, 

 was, with the mineral manure alone 4 tons 14 cwt, with the 

 addition of nitrate 16 tons 1 cwt., with that of ammonium- 

 salts 14 tons 1 cwt., with rape-cake 18 tons 9 cwt., and with 

 ammonium-salts and rape-cake together 22 tons 15 cwt. 



With the comparatively limited growth of turnips potash Potash. 

 manures had little effect ; but here, after years of further ex- 

 haustion of the potash within the soil, and with so much 

 more vegetable matter produced, the deficiency of potash 

 where it had not been applied is very obvious. Thus with 

 ammonium-salts and superphosphate the average produce 

 was only 8 tons 1 cwt. ; but taking the mean of plots 6 and 

 4 with the ammonium-salts, superphosphate, and potash also, 

 the average produce was 14 tons 1 cwt. Again, with super- 

 phosphate and rape-cake, the average produce was only 11 

 tons 12 cwt., but that of plots 6 and 4 with potash in addi- 

 tion was 18 tons 9 cwt. Lastly, with ammonium-salts, rape- 

 cake, and superphosphate, the average produce was only 10 

 tons 17 cwt, but that of plots 6 and 4 with potash in addi- 

 tion was 22 tons 15 cwt., or more than twice as much. 



In reference to the average results over the 17 years shown Effect of 

 in the table, it may be stated that in favourable seasons very season - 

 much larger crops were obtained. Indeed in several seasons 

 more than 30 tons of roots have been obtained by farmyard 

 manure and artificial nitrogenous supply in addition; whilst ' 

 in one case with the full mineral manure, including potash 

 and the highest nitrogenous supply, more than 37 tons was 

 obtained. 



The proportion of leaf to root will be considered further Manures 

 on ; but the table shows that the actual amount of leaf was andlea f- 

 very much increased by the nitrogenous manures, and that tion. 

 with farmyard manure and the highest artificial nitrogenous 

 supply, there was an average of nearly 6 tons of leaf. 



The lower division of the table shows in several cases an Large 

 average total produce, root and leaf together, of nearly 30 yields, 

 tons, and in some years there has been more than 40 tons. 

 The very great power of utilising manure and of producing 

 vegetable substance possessed by the mangel is thus strik- 

 ingly illustrated. 



It has sometimes been assumed, however, that by virtue of Do roots 

 the lar<re amount of leaf-surface which root-crops expose to drawn i tro ~ 

 the atmosphere, they obtain a large amount of their nitrogen theairi 

 from that source. It is further assumed that if a small 

 quantity of nitrogenous manure be applied so as to favour 

 the early development of the plant, it will then obtain the 



