164 EXPERIMENTS WITH THE PHOSPHATES. 



quantity was applied again. The following were the weights 

 of hay yielded by the two plots during the three years : 



1844. 1845. 1846. 



Nothing gave . . 3820 4486 3330 



Phosphate of soda . 4326 4657 3573 



Increase, . . 506 171 243 



An increase in each year was thus perceptible ; but only in 

 the first year can the differences be regarded as greater than 

 the ordinary variations to be expected in different portions of 

 the same field. 



2. Along with superphosphate of lime, both of the above 

 phosphates were applied by Mr Lawes, in 1844, to his turnip- 

 crop, at Rothampstead farm, Herts, with the following results: 



No manure, gave ... 2 tons 4 cwt. of bulbs. 



Farm-yard manure, 12 tons, . 10 ...15 ... 



Superphosphate of lime, 1 cwt., I g 13 



Phosphate of soda, 4 cwt., J 



Superphosphate of lime, 1 cwt., ) ~ 



Phosphate of potash, 4 cwt., j 



Superphosphate of lime, 1 cwt., ) _ -^ % 



Phosphate of magnesia, 4 cwt., j 



These experiments are insufficient to throw any light on the 

 special action of the several phosphates employed. We have no 

 experiment with the superphosphate applied alone at the rate 

 of 1 cwt. per acre, and we have no trials in duplicate. The 

 results appear to say that the effects of the three phosphates of 

 potash, soda, and magnesia, applied in equal quantities, are 

 sensibly alike, which can scarcely be the case under any ordi- 

 nary circumstances of soil or crop. * 



6. Suggestions for comparative experiments with the 

 phosphates of potash and soda. 



As phosphoric acid is so necessary a food to plants, and as 



its compounds with potash and soda are very soluble, there is 



reason to believe that on certain soils, for certain crops, and 



applied at certain seasons of the plant's growtn, they might 



* Journal of the Royal Society, vol. viii. p. 510. 



