558 EEroKT— 1880. 



require 7'3 per cent, of that substance. The advantage gained hj the use of sul- 

 phate of magnesia, as shown hy these experiments, was : — 



Magnesia 

 in Asli being 



For Turnips .... 15|^ per cent. 3-09 

 For Potatoes ... 30 „ 5-55 



For Clover and Rye Grass . 130 „ 7-3 



If this coincidence is accidental it is extraordinary. Another point to which I 

 wish to call attention is the fact that the advantage gained is manifestly largely 

 due to the magnesia, and not to the sidphuric acid only ; for where the advantage 

 was the greatest by far, the sulphate of lime did not produce an equivalent effect, 

 though the 3 cwt. of calcic manure carried to the soil upwards of six times the 

 amoimt of sulphuric acid that the li cwt. of the magnesic salt supplied, and 

 though the latter is far more soluble than the former, gypsum is sufficiently soluble 

 for all the requirements of plants. 



A third point remains for remark, and that is the relative effect produced on 

 potatoes in the above experiments of Mr. Fleming, of Barochan, by the use of dimg 

 No. 1, of sulphate of magnesia No. 2, of sulphate of soda No. 3, of nitrate of soda 

 No. 4, and of a mixture of nitrate of soda and sulphate of magnesia No. 5. A 

 comparison of these residts can leave little doubt in the mind of the immense value 

 of magnesia as an ingredient of a manure for potatoes. By the addition of 2 cwt. 

 of sulphate of soda to the dmig no advantage was gained ; when 1^ cwt. of nitrate 

 of soda was added to the dimg, the extra supply of nitrogen in its nitric acid 

 increased the produce 30 per cent. ; but when 1 cwt. of sulphate of magnesia was 

 added to the dimg, together with 1 cwt. only of nitrate of soda, the amount of 

 produce rose upwards of 76 per cent, upon what was given by dimg alone. More- 

 over, it is quite clear that as the li cwt. of nitrate of soda alone gave an increase of 

 only 30 per cent., and when sulphate of magnesia was added to the manui-e, the 

 nitrate at the same time being reduced by 50 per cent., the produce rose to 76 per 

 cent., more than one-half of the advantage was due to the sulphate of magnesia. 

 I have before showai and my conclusions are confirmed bj' these experiments, that 

 the benefit is chiefly attributable to the magnesia, and not to the sidphuric acid 

 combined with it. There is, indeed, one other possible supposition at ^'ariance mth 

 this conclusion, ^■i7.. that the Ih cwt. of nitrate of soda was too large a quantity to 

 use per acre ; iDut all experience contradicts this idea. 



The followiag are the results recorded by Professor Johnston of the experiments 

 on cereals, as far as they affect our investigation. The quantities of manure and 

 the crops are, per acre : — 



With Barley, Common White. 

 Nothing gave 3400 lbs of straw and 47'25 bushels of grain, 



li cwt. sulphate of soda ) gggg 54.9 



1 „ „ magnesia | " " jj 77 



With Oats, 2nd crop after old lea. the Manure applied as top dressing 

 t%vo months after sowing. 



Nothing gave 2896 lbs. of straw and 54 bushels of gi'ain. 



16 cwt. rape dust „ 2592 „ 44-96 „ 



1 cwt. sulphate of soda „ 2792 „ 38-56 „ 



With Spring JJ^ieat after Turnip. 

 Nothino- gave 4056 lbs. of straw and 47-68 bushels of grain. 



16 cwt°rape dust „ 4600 „ 51-05 „ 



1 cwt. sulphate of soda „ 3864 „ 38-00 „ 



With Winter TVheat as top dressing. 

 Nothing gave 2560 lbs. of straw and 24-93 bushels of grain. 



841bs. sulphate of magnesia I o-^qq 28-4 



5 cwt. rape dust i " " " " 



