Sir Daniel Hall 121 



has written a book on these experiments, which is full of 

 interesting tables showing the different crops given by 

 the use of different manures. For instance, hay. Hay 

 grown on unmanured land at Rothamsted over a period 

 of forty-seven years averaged only twenty-three hundred- 

 weight to the acre. Hay grown with a complete mineral 

 manure but with no nitrogen gave thirty-nine hundred- 

 weight to the acre, but hay on a plot fully manured ran 

 to no less than sixty-four hundredweight per acre. 



One patch of land at Rothamsted has been cropped for 

 years without being given any fertilizer at all, and the 

 nitrogen loss has been noted. The nitrogen goes on 

 dwindling year by year. Another field has been allowed 

 to lie fallow for twenty-five years. The self-sown grasses 

 and weeds are never taken away, but allowed to rot 

 where they lie. This land is improving, and the amount of 

 nitrogen contained in it is increasing. What is happening 

 is that a kind of bacterium called the azotobacter is able 

 to work among the dying vegetation and to fix a certain 

 amount of nitrogen from the air. 



A few years ago efforts were made to ' domesticate ' the 

 azotobacter and inoculate soil with it. But as yet this 

 experiment has not been very successful, and Sir Daniel 

 Hall says, " The picture of the farmer carrying the manure 

 for a field in his waistcoat pocket and applying it with a 

 hypodermic syringe is still a vision of the future/ ' 



Air, as we all know, consists largely of nitrogen gas, and 

 since supplies of nitrogen from other sources have been 

 running short the scientists have invented ways of getting 

 nitrogen from the air for use on the land. In the great 

 plant at Bellingham, near Darlington, thousands of tons of 

 nitrates are manufactured yearly from the air by an 

 electrical process ; in Norway and Germany there are large 

 factories for the same purpose. At Bellingham nitrate of 

 ammonia is combined with chalk into what is called nitro- 

 chalk, which is a most valuable fertilizer. 



