64 MODE IN WHICH GYPSUM ACTS. 



results of experimental farming in this country are to be trusted, this is 

 by no means the case. The action neither of this, nor probably of any 

 other inorganic substance applied to the soil, is to be explained by a 

 reference in every case to one and the same property only. 



7°. The presence or evolution of ammonia in a soil containing animal 

 and vegetable matter in a decaying state, induces or disposes this mat- 

 ter to attract oxygen from the air more rapidly and abundantly. The 

 result of this is, that organic acid compounds are formed, which combine 



applied. Tlie first crop was cul for hay, and the second ripened for seed. TJie following 

 were the comparative results per acre : 



HAY CROP. SEED. STRAW. 



cwt. grs. Ihs. cwt. qrs. lbs. 



Gypsumed 60 3 21 22 3 12 



Unmanured 20 20 5 



Excess of produce . . 40 3 1 17 3 12 



The excess of produce in all the three crops upon the gypsumed land is very large : let us 

 calculate how much nitrogen this excess would contain. In a previous lecture (II. p. 30) it 

 was stated as the result of Boussingault's analyses, that dry clover seed contained 7 per 

 cerit. of nitrogen, and the same experimenter found in the hay of red clover 1^ per cent, (or 

 70 and 15 lbs. respectively in lOCW.) 



The seed as it was weighed by Mr. Smith would still contain one-ninth of its weight of 

 water, and, consequently, only 6>^rd per cent, of nitrogen, [.see Lecture II. p. 30.] Let it 

 be taken at 6 per cent, and let the straw be supposed to contain only 1 per cent, of nitro- 

 gen, the quantity of this element being found to diminish in the grasses after the seed has 

 ripened, and averaging 1 per cent, in the straw of wheat, oats, and barley, the weight of ni- 

 trogen reaped in the whole crop will then be as follows : 



1. 40 cwt. of hay (4480 lbs.) at 1§ per cent, of nitrogen, contain 67 lbs. 



2. 85 lbs. of seed at 6 per cent, contain 5 lbs. 



3. 17 cwt. 3 qrs. 12 lbs. or 2000 lbs. of straw at 1 per cent, contain 20 lbs. 



Total nitrogen in the excess of crop, 92 lb.=?. 



But, as above shewn, the fi%'e bushels or four cwt. of gypsum could fix only 90 lbs. of am- 

 monia containing 74 lbs. of nitrogen, leaving, therefore, 18 lbs. or one fifth of tlie whole, to be 

 derived from some other source. 



Now this result supposes that none of tlie gypsum or sulphate of ammonia was carried 

 away by the rains, but that the whole remained in the soil, and produced its greatest jwssihle 

 eff*ect on the clover — and all in one season. 



But the effect of the gypsum does not disappear with the crop to which it is actually ap- 

 plied. Its beneficial action is extended to the succeeding crop of wheat, and on grass lands 

 the amelioration is visible for a succession of years. If, tiien, the increased produce of a 

 single year may contain more nitrogen than the gypsum can be supposed to yield, this sub- 

 stance must exercise some other influence over vegetation than is involved in its supposed 

 action on the indefinite quantity of ammonia in the almospliere. 



2'^. Again, Mr. Barnard, of Little Bordean, Hants, applied 2| cwt. per acre on two-year 

 old sain foin, on a clayey soil. The increased produce of the first cutting was a ton per 

 acre, and in October fully a ton. the undressed part yielding scarcely any hay at all, while 

 the dressed part gave \\ tons. The second year no gypsum was applied, and the diflTerence 

 is said to have bebn at least as great. 



Supposing the increased produce in all to have been 4 tons of hay, and the nitrogen it con- 

 tained to have been only one per cent. — the 4 tons (8960 lbs.) would contain about 90 lbs. of 

 nitrogen. But 2§ cwt. would fix only 46 lbs. of nitrogen in the form of ammonia ; and there- 

 fore, supposing it to have produced its maximum effect, there remain AA lbs. or nearly one 

 half of the whole, unaccounted for by the theory. 



I would not be understood to place absolute reliance on the results of the above experi- 

 ments ; but the way in which such results may be easily applied for the purpose of testing 

 theoretical views, will, I hope, convince ttie intelligent practical agriculturist how important 

 it is, that the results of some of the experiments he is every year making should be accu- 

 rately determined by weight and measure. By this means data would gradually be accu- 

 mulated, on which we might hope to found more unexceptionable explanations of the phe- 

 nomena of vegetation, than the results obtained in our laboratories liave hitherto enabled 

 us to advance. 



In a subsequent note it will be shewn that the mode in which the nitrates of soda and 

 potash act — in other words, the theory of their action upon vegetation — may be tested by a 

 similar simple calculation, and the importance of precise experiments made on the farm 

 will then still further appear. It is in the hope of inducing some of my readers to make 

 comparative trials and publish accurate results, that I have introduced into the Appendix 

 (No. I.) an outline of the mode in which such experimenis laay most usefully be performed. 



