Importance of Nitrogen to Growth of Plants. 227 



twice its weight of water for three minutes, then allowing it to stand 

 for thirty minutes, after which the water is poured off, filtered through 

 a Chamberland filter and the nitrates in this extract determined. 

 Whether this conventional method of determining the nitrogen in the soil 

 is a measure of the nitrogen available as plant-food is, of course, open to 

 debate. In this paper it is assumed that the water-soluble nitrate is a 

 measure of the available nitrogen. Ammonia compounds have been 

 shown, however, to be available to certain crops. The water-soluble 

 nitrogen is stated as the acid radical NO3 in parts per million of dry 

 soil. It is important to note that if the amount of nitrogen determined 

 by this method represents the nitrogen actually in solution in the soil, 

 then stating the nitrogen in parts per million of dry soil does not show 

 the concentration of the soil solution. Suppose a soil containing 10 per 

 cent, of moisture contained 30 parts of NO3 per million of dry soil, then 

 a soil containing 20 per cent, of moisture should, on the above assump- 

 tion, contain 60 parts of NO3 if the soil solutions have an equal con- 

 centration of NO3. 



It is also important to recognize that the water-soluble nitrogen is 

 an extremely small part of the total nitrogen of the soil. During 1905, 

 Bizzell found, as the result of 32 determinations, that on August 21, 

 Dunkirk clay loam growing alfalfa contained 6,910 parts of total nitrogep 

 stated as NO3 in each million pounds of dry soil, while on the same 

 soil on the same date as the result of 96 determinations there were 49.7 

 parts of water soluble NO3. In other words, there were 139 times as 

 much total nitrogen as water-soluble nitrates. It must be apparent to 

 every one from these statements that the methods that have thus far been 

 employed are open to many objections. Nevertheless, I think some 

 progress is being made in the study of these soil questions. 



The purpose of cultural methods. 



The Lord said, " Let there be light, and there was light." No one 

 doubts that light was of prime importance in the creation of the world 

 and still is an important factor of plant growth. 



That too little or too much heat or moisture may be injurious to 

 plants does not admit of discussion. Further it is well known that 

 different species have adapted themselves to different amounts of light, 

 heat, and moisture. In 1901 the yield of maize was 1,522 million bushels 

 in the United States, in 1902 it was 2.523 million bushels. No one doubts 

 that this was due in the main to differences in sunshine, heat and rain- 

 fall. That the precipitation is of vast importance and often the control- 

 ling influence in the yield of crops has been demonstrated by many experi- 

 ments. It goes without saying that plants cannot be built up of ten 



