ii' MGYWIAA 1 AGH1CULTUHK 



life without destroying or lessening the substances for 

 the production of new life. 



In the atmosphere there are minute quantities of com- 

 bined nitrogen in the form of ammonia, nitric and nitrous 

 compounds, and organic matter, which ultimately fall on 

 the earth in the waters of rain and dew. These substances 

 are important plant foods because of the nitrogen con- 

 tained in them, but the quantity received from the air in 

 this way is small. It varies in different places and years. 

 In England, at Rothamsted, it has been found to amount 

 to about 4*4 rotls of nitrogen per feddan, per annum, 

 consisting of 2*4 rotls as ammonia compounds, 1 rotl as 

 nitrates and nitrites, and 1 rotl as organic nitrogen. In 

 Egypt the rainfall is small, amounting to about 3*5 centi- 

 metres per annum in the neighbourhood of Cairo, and 

 the gain of nitrogen to the soil by means of the rain is 

 Therefore also small. Rain water collected at Ghizeh 

 during the winter of 1900-1901, amounting to 3*625 

 centimetres, was found to contain nitrogen equivalent to 

 94 grams per feddan (a little more than one fifth of a 

 rotl) made up of 57*6 grams as compounds of ammonia, 

 1 7'4 grams as nitrates and nitrites, and 19 grams as organic 

 nitrogen. This quantity is so small that it may be 

 altogether neglected when considering the sources of soil 

 nitrogen. Dust and smoke in the atmosphere are very 

 hurtful to plants when they occur in any considerable 

 quantity. 



Climate in relation to agriculture. In this connection 

 the physical conditions of the atmosphere light, temper- 



