WASTES IX RELATION TO AGRICULTURE AND FORESTRY 



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as cotton ginning, feed grinding and mixing, and 

 most harvesting operations. The dust varies from 

 small particulates of the product being processed 

 to fine powders of organic material including 

 spores and soil that may be attached to or inter- 

 mingled with the product. Depending on circum- 

 stances, the dust may fall out quickly or may be 

 carried long distances by wind. 



Research has led to relatively efficient collecting 

 devices for larger particles. Cyclones — mechanical 

 dust removers — are widely used on feed grinding 

 and mixing equipment; when properly designed 

 and used they will collect all but very fine dusts. If 

 more stringent requirements for dust removal are 

 imposed in the future, new techniques will need to 

 be developed. 



Cotton ginning presents a special problem in 

 that the lint fly is mingled with other dust and both 

 are exhausted with air used to transport cotton 

 through the gin. Research to date has greatly im- 

 proved screens for collecting the lint fly. One major 

 accomplishment was the development of a self- 

 cleaning screen to permit continuous operation and 

 to permit maximum effectiveness of the screen. 

 Current studies are investigating wet and dry 

 inertia! separators, electrostatic collectors, special 

 screens to collect very fine particles, and methods 

 to measure air pollution quantities and distribu- 

 tions from co + ton gins. 



The general problem of control of fine particles 

 suspended in turbulent conveying media, such as 

 air, is being studied by the U.S. Department of 

 Agriculture in one of its pioneering laboratories. 

 Research emphasis is directed toward developing 

 a mathematical formula to characterize the com- 

 plex system of fine particles. This would aid in 

 their measurement, classification, and control. 



Sediment 



Conservationists in the United States have been 

 concerned over excessive delivery of sediment from 

 cultivated land to streams for over 200 years. 

 Around 1750 Jared Eliot of Connecticut was writ- 

 ing on the seriousness of soil erosion and stream 

 sedimentation. Jolm Taylor of Virginia published 

 a vigorous essay in 1813 on ways to reduce soil 

 erosion, to control gullies, and to prevent stream- 

 bank erosion and stream sedimentation. Many 

 leading agriculturists made a contribution, \mt lei 

 us especially consider the work of E. W. Hilgard. 



Sediment Delivery 



Hilgard must be regarded as the most dis 

 guished soil scientist the United States has pro- 

 duced. From 1855 to 1873, he was State Geologist 

 of Mississippi. In 1860, he published a book en- 

 titled "A Report on the Geology and Agriculture 

 of the State of Mississippi"' — a contribution that 

 is now regarded as one of the "classics" in history 

 of American agriculture. 



Hilgard noted in this book that the brown loam 

 soils in north-central Mississippi were some of the 

 most fertile cotton-producing soils in the South. 

 But he warned that these soils were prone to what 

 he called "running," and that unless proper "hus- 

 bandry" practices were followed, the soil would 

 run off the fields into the streams filling up the 

 channels. 



Soon after Hilgard's report was published, the 

 Xation erupted into a violent holocaust. During 

 the war years and the turbulent years of the Re- 

 construction, little, if any, thought was given to 

 the problems of soil erosion and attendant sedimen- 

 tation. 



That which Hilgard warned might come to pass, 

 did come to pass. 



By the turn of the century, the U.S. Depart- 

 ment of Agriculture and several State agricul- 

 tural experiment stations were providing technical 

 advice on field management practices to reduce 

 soil erosion and the movement of sediment from 

 fields to streams. Several States began measuring 

 soil and water losses from different kinds of lands 

 in the early 1900's. 



But the decade beginning in 1928 stands out as 

 the period when the soil and water conservation 

 movement began to flourish in this country. This 

 era saw the establishment of soil and water con- 

 servation programs within the U.S. Department of 

 Agriculture in both research and operations, 

 which have evolved as major bulwarks in the con- 

 servation development of the Nation's land and 

 related water resources. 



Research was begun and has continued on the 

 mechanics of erosion and factors influench 2 

 sion processes; mechanics of sediment transport: 

 principles o( sediment deposition in stream chan- 

 nels and on flood plains: rates and processes of 

 reservoir silting: sediment burden of streams in 

 relation to erosion processes in contributing water- 



