488 ANNUAL REPORT OF THE Off. Doc. 



be derived from the practice. It will result, not only in building 

 up soils poor in that important element, nitrogen, but will contribute 

 materially to the improvement of their physical character, the water- 

 holding capacity, and their consequent crop-producing power. On 

 soils rich io potential fertility, the continued and judicious use of 

 green manures will materially improve the mechanical character 

 of the soil, not only, but will be very influential in the maintenance 

 of fertility, without large additions of the minerals, phosphoric 

 acid and potash. 



The Amount of Nitrogen Contained in Average Crops. 



While it has already been pointed out that it is very difificult to 

 estimate the amount of nitrogen that the leguminous crops will 

 draw from the air, the following tabulation shows the nitrogen 

 and organic matter that are contained in an ordinary crop of the 

 various plants: 



Cow peas, 



Soy beans, 



Crimson clover, .. . 

 Alsike clover, . . . 



Red, clover, 



Canada field peas 



If the amounts of nitrogen indicated in the table as contained 

 in a crop that can be harvested were all gathered from the air, 

 there would be an undoubted increase in the fertility of the soil, as 

 the amount of nitrogen gathered is equivalent to that contained 

 in from 320 to 400 pounds of nitrate of soda, which amount would 

 be regarded as a heavy dressing for even vegetable crops. Inter- 

 preted in terms of yard manure, the nitrogen and vegetable matter 

 would be equivalent to from six to eight tons of average yard ma- 

 nure. It must be remembered too, that the yields given are not 

 large, and that they do not include the amount of nitrogen and 

 organic matter that may be contained in the roots and stubble, 

 which in the case of the clovers is very considerable. 



Furthermore, experiments have shown that the rapidity with 

 which the organic matter will decay and give up its nitrogen to 

 the cereal group of plants, is such as to make this source of nitrogen 

 compare favorably with that contained in the average commercial 

 fertilizer. The fact that so large an amount of nitrogen is intro- 

 duced by means of green manures, whether entirely drawn from the 



