59 

 INFLUENCE OF SULPHATE ON WEIGHT OF PRODUCE. 



At Rothamsted, in the first twenty years of experiment, 

 the following were the average weights of hay per acre 

 per annum, produced on the plots mentioned : 



TABLE XXXVIII. 



T/nmanured 21 cwt. 



Mineral manures 3o| ,, 



Minerals and ammonia salts 51 ,, 



Minerals and nitrate of soda 57 



Both the nitrogenous manures gave a very large increase 

 when used with minerals ; but nitrate of soda produced 

 considerably more hay on the average than ammonia salts. 

 In comparing these two manures in order to estimate their 

 use on the farm, however, we must remember that, used 

 over a long series of years in large quantities, ammonia 

 salts cause a heavy loss of lime from the soil, and the land 

 therefore becomes sour and unfavourable for plant growth, 

 especially in the case of permanent grass. Thus at Rotham- 

 sted, after a time, the soil of plots dressed with ammonia 

 salts became so sour that in 1881 part of each plot was 

 dressed with chalk, to sweeten the land and replace the 

 lime which had been lost. The effect of this was to increase 

 the yield of these plots, and check the deterioration which 

 had occurred up to that time. In ordinary farm practice, 

 this souring of the soil would not occur to the same extent ; 

 and the two manures, sulphate and nitrate, would act 

 under more equal conditions. We see this in the average 

 results for the first seven years of experiment on the plots 

 at Rothamsted mentioned above. The average produce of 

 hay per acre per annum for that period was 



TABLE XXXIX. 



Unmanured 25$ cwt. 



Mineral manures 35 ,, 



Minerals and ammonia salts otij ,, 



Minerals and nitrate of soda (five years only) . . 5l| 



At first, then, ammonia salts gave the higher produce ; 

 but owing to their continuous application, the crop became 

 unhealthy, so that over the longer period nitrate produced 

 the heavier average yield. 



Generally, therefore, in experiments on grass land on the 

 continuous use of manures, we find that nitrate gives the 

 higher yield of grass or hay per acre. Thus in the experi- 

 ments carried out by the Highland and Agricultural Society, 

 at Pumpherston, nitrate with superphosphate and potash 

 salts gave an average of 35-4 cwt. of hay, against 32-8 cwt. 

 yielded by sulphate of ammonia with the same mineral 

 manures. In the grass experiments at the Roya Agricul- 



