8 CITY STREET SWEEPINGS AS A FERTILIZER. 



An examination of the figures in the table shows that the sweepings 

 and stable manure had about the same efficiency in causing increased 

 growth. This is true with both the grain and the vegetable crop. 



The oil was also extracted from the sweepings by using ether as the 

 solvent, and the sweepings afterwards tested in soils. Tliis test also 

 showed that the sweepings were practically as good as the stable 

 manure. 



It will be recalled that the effect of the unextracted sweepings was 

 not nearly so good as the effect produced by the stable manure. In 

 other words, after the oil was removed from the street sweepings their 

 action was practically the same as that of the stable manure. That 

 the oil is the deleterious constituent of the sweepings is also borne out 

 by the fact that the oil itself when added to culture solutions in which 

 plants were growing markedly reduced their growth. 



The application of street sweepings to soils will undoubtedly have 

 a beneficial effect and be a factor in building up the land. The pos- 

 sible danger of a harmful effect from the oily substance which it 

 contains must, however, be considered. If the oil could be econom- 

 ically extracted this danger would be averted. The oil in the debris 

 for the first year or two may not have any effect, but a continuous 

 application to a field year after year may eventually impair its pro- 

 ductiveness, unless through drainage or other natural agencies the 

 oily material is drained off or changed. In some localities this is 

 probably the case, as the use of such material is still said to be 

 effective, although it has been applied for a number of years. No 

 very definite field information on this point is, however, at hand. In 

 this connection attention must be called to the fact that the pres- 

 ence of an unusual amount of oil in such street sweepings has been 

 the result of automobile traffic, and hence appears only in recent 

 years as an appreciable factor in the use of street sweepings as fer- 

 tilizer, and it is not improbable that the amount of oil will even 

 further increase in the next few years. 



Aside from the physiological action of the oily material here men- 

 tioned, there are probably other more strictly physical effects, due to 

 the coating of soil particles and consequent interference with normal 

 moisture movement and solubility of the mineral soil constituents. 



Vegetable or animal oils undergo changes in soils under the influence 

 of soil organisms, but so little is 'known concerning the action of 

 organisms on the strictly hydrocarbon oils that no statement con- 

 cerning the possible disappearance or change of this oil in street 

 sweepings can be made. 



Approved : 



JAMES WILSON, . 



Secretary of Agriculture. 

 Washington, D. C., March 24, 1912. 



O 



