SOIL IMPROVEMENT 1 17 



that rainless, tropical climate the moisture evaporated, leaving 

 the fertilizing elements uninjured. The ancient Peruvians knew 

 the value of these deposits, and protected the sea fowls and their 

 homes. It was forbidden under penalty of death to kill the birds 

 or even to set foot on the islands during the breeding season. 



About eighty years ago the first cargo of guano was sent to Eng- 

 land, and experiments proved that it had a wonderful effect on 

 crop production. Millions of tons were shipped until the best beds 

 were exhausted. Deposits have been found in other places, but 

 none so rich in nitrogen as the old beds off the Peruvian coast. 



Nitrogen. For soil nitrogen, a farmer should rely chiefly on 

 raising legumes, on proper rotation of crops, on stock raising and 

 the use of manures, and on deep plowing and thorough cultivation ; 

 thus bacteria supply the soil with nitrogen. 



The chief commercial forms of nitrogen are : guano ; nitrate of 

 soda, which is a vast natural deposit in rainless districts of South 

 America ; sulphate of ammonia, which is obtained as a by-product 

 in the manufacture of illuminating gas from coal and from other 

 sources ; cotton-seed meal, which is a by-product of the manufacture 

 of cotton-seed oil ; dried blood and tankage, which are by-products 

 from slaughter houses ; dried fish and fish scraps, which are by- 

 products of fish-oil factories and canneries. 



The value of fish as a fertilizer was known to our American 

 Indians. You remember that Squanto taught the New Eng- 

 land settlers that they could increase the yield of corn by putting 

 a fish under each hill. This gave the grain the two elements it 

 needed most phosphoric acid and nitrogen. 



Commercial nitrogen was until recently obtained- entirely from 

 natural deposits and products. Artificial nitrates are now being 

 made by the use of electric furnaces. By these the nitrogen and 

 oxygen of the air are made to unite, forming nitric acid. 



