556 REPORT— 1880. 



To pursue this subject further in tlie direction indicated by Liebig is a task for 

 which 1 feel myself unequal ; but it encourages me to examine narrowly the records 

 of experiments in which magnesia has been made an element of mamu'es, or has 

 been tried alone, or in conjunction with an acid. 



Of experiments made with magnesia alone I know of no further instances of a 

 definite and reliable kind than those of Donaldson, above quoted ; but concerning 

 experiments with sulphate of magnesia, both alone and combined with other con- 

 stituents, there are records to which I can refer for further proof of my argument. 



Before doing so, however, I wish to call attention to a fact which has a con- 

 siderable bearing on the case. Both Liebig and Ville hold that farm-yard manure — 

 excellent manm-e as it is — must be supplemented with mineral substances if full 

 value is to be given to it, and that additional phosphoric acid is necessai-y to make 

 all of its nitrogen available for plant life. Now, in 100 parts of farm-yard manure 

 there is less than -14 per cent, of magnesia, and of its mineral constituents the 

 magnesia forms only 1'7 per cent. Donaldson tells us 'the quality of earthy 

 composts and of farm-yard manure is prodigiously improved by a mixtui-e of 

 seaweed. . . . During the seasons of the seaweed coming on shore the farmers 

 have heaps of dimg or soil in readiness to receive the immediate benefit of the 

 " vrrack," and these heaps, along with any lands which may be in a state fit to 

 receive it, afford a ready application of this invaluable article. Farm-yard manui-e 

 for turnips is improved by it almost beyond description, and never fails to vindicate 

 the expectations of its effects.' (Donaldson, p. 12.3.) 



Now, what are the components of the ash in seaweed ? No less than from 7 

 to 20i per cent, of magnesia are fomid in different kinds of it, and the ashes of the 

 seaweed at the mouth of the Mersey contain upwards of 15 per cent. No doubt 

 in the growth of the turnip crops the advantage is largely derived from the great 

 amount of potash the seaweed contains, but of this substance the ash of dung itself 

 j-ields upwards of 9 per cent., whereas it yields only, as stated, 1'7 per cent, of 



magnesia. In the asli of dung, therefore, i ^ = ~ ; in that of the turnip 



magnesia 1 



? _ — . In seaweed it = -^ ; it is reasonable, therefore, to suppose that the 



magnesia i 1 



turnip, if manured with seaweed as well as dung, derives more of the benefit from 



the magnesia added by the seaweed, than from the potash thus supplied. 



We will now proceed to examine some of the experiments made in 1842, and 

 reported by Professor Johnston, wliich have been already briefl}' referred to. 



Results of Experiments with Sulphate of Magnesia. 



1. On Yellow Turnips, by Mr. McLean, Braidwood, Midlothian, 1842. 



Farmyard manure, 30 carts . . , produced, per acre, 24 tons. 

 „ „ with i-cwt. of sul- I g_c 



phate of magnesia mixed with it . j " " "' " 



Or the increase gained by |-cwt. of sulphate of magnesia was 4 per cent. 



2. On Yellow Turnips, by Mi-. Fleming, Barochan, Renfrewshire, 1842. Variety, 

 ' Early Liverpool.' 



Notliing, 1st plot 11-4. 



2nd plot _ 12-85. 



Sidphate of magnesia, 1 cwt 14-85. 



Here 1 cwt. of sulphate of magnesia alone gives an increase of upwards of from 

 12 to 30 per cent, (mean, 21 per cent.) ; but as the sulphate of magnesia was not 

 tried in duplicate, less reliance can be placed on this experiment. 



3. On Potatoes, variety 'Early Americans,' carried out bv Mr. Fleming, Barochan, 

 in 1842. 



Intended to test the comparative advantage of sulphate of magnesia when 

 applied as a top dressing to the young plant, and when mixed with the manure at 

 the time of its application. 



