30 



mineral substances it requires. If not, a comparatively 

 small dressing of the nitrogenous manure is likely to pro- 

 duce all the possible injurious effects to an exaggerated 

 degree. If, on the other hand, all the essential mineral 

 substances are in abundance, a comparatively large dress- 

 ing of nitrogenous manure will only stimulate a strong but 

 healthy growth, and will therefore prove remunerative. A 

 balance or proportion between the mineral and nitrogenous 

 manures is the important thing. Failure to realize this is 

 one of the common causes of unsatisfactory results from the 

 the use of nitrogenous manures, and is chiefly responsible for 

 the exhaustion of the soil which sometimes follows their use. 



EFFECT OF SULPHATE OF AMMONIA ON THE SOIL. 



The effect of sulphate of ammonia on the soil must also 

 be mentioned. In explaining the action of the soil in ab- 

 sorbing ammonia, it has been stated that when sulphate 

 of ammonia comes into contact with carbonate of lime 

 in the soil, carbonate of ammonia and sulphate of lime are 

 produced, of which the last named is washed away in large 

 quantities in the drainage water. Loss of lime, therefore, 

 follows the use of sulphate of ammonia. Under any condi- 

 tions likely to arise in ordinary farm practice, this will not 

 be of much consequence, except on soils specially deficient 

 in lime. Even then an occasional liming will supply all 

 the lime required, and will in any case be useful or even 

 necessary to the soil, quite apart from the effects of 

 sulphate of ammonia. In long-continued experiments in 

 continuous cropping and manuring, however, such as those 

 at Rothamsted and Woburn, where in some cases very 

 large dressings of ammonia salts are given every year, the 

 soil after a time shows clearly the effects of this removal of 

 lime. It becomes very sour, and the crops grown become 

 unhealthy. For instance, in the Woburn permanent barley 

 experiments, the average produce per acre from the use of 

 ammonia salts, which, in the first three periods of five years 

 each, had been 36-6 bushels, 42-2 bushels, and 34-5 bushels 

 per annum respectively, fell to 21 bushels per annum for 

 the fourth period the sixteenth to the twentieth years of 

 the experiment a proportionately greater falling off" than 

 occurred on the plots where ammonia salts were not em- 

 ployed. 



When a soil has thus been robbed of its lime, it becomes 

 like one naturally deficient in that constituent its absorp- 

 tive power for ammonia is injured, and nitrification may 

 be stopped for want of a base to combine with the nitric 

 acid as it is formed. We must repeat, however, that 

 these extreme effects are not likely to result under the 

 usual management of a farm, in which sulphate of 

 ammonia is only used occasionally, and in comparatively 

 small quantities. 



