PROBLEMS FROM LAND OCCUPANCY 167 



was more than 100 times the least. 5 For this reason the quantita- 

 tive studies of areas at least several acres in extent are likely 

 to give more reliable estimates of average infiltration. 



The effects of agricultural land use upon rates of infiltra- 

 tion have been shown both by comparison of cultivated or 

 bare areas with adjacent areas having native cover, and by al- 

 ternating cultivation and noncultivated cover on a single ex- 

 perimental area. It has been found that the effect of cover 

 upon infiltration capacity may be more important than soil 

 type: 6 this is true particularly of the broad group of soils in 

 which clay is an important constituent. Some experiments have 

 shown a greater degree of variation in infiltration capacity re- 

 sulting from surface conditions on a single soil, than is found 

 on different soils having the same surface conditions. 7 In stud- 

 ies of three plots of the same type of soil, the infiltration ca- 

 pacity of a cultivated plot was found to be only one-fourth of 

 a plot with native grass cover, and less than that of a bare, un- 

 cultivated plot. 8 The program of the experiment stations of 

 the U.S. Soil Conservation Service has included studies of in- 

 filtration and runoff from representative soils in all parts of 

 the country. Results of these studies were summarized in 

 1940, 9 and further analyses of data have been presented in a 

 series of recent technical papers. 10 



The effects of grassland and forests upon the disposal of the 

 water falling as precipitation have been determined by the 

 same techniques as for cultivated or bare land, and indeed 

 very commonly in the same experiments, so that comparisons 

 are readily available. The most widely recognized benefits of 



s Rowe, P. B., "The Construction, Operation, and Use of the North Fork 

 Infiltrometer," Flood Control Coordinating Comra. Misc. Pub. 1, Calif. Forest 

 and Range Exp. Sta., 1940, 64 pp. 



e Lewis, M. R., and W. L. Powers, Soil Sci. Soc. Am. Proc, pp. 334-339, 1938. 



7 Duley, R. I., and L. L. Kelly, Nebr. Agr. Exp. Sta. Research Bull. 112, 1939. 



s Muckel, D. C, Some Factors Affecting the Rate of Percolation on Water- 

 spreading Areas, Trans. Am. Geophys. Union, vol. 17, pp. 471-474, 1936. 



9 Free, G. R., G. M. Browning, and G. W. Musgrave, op. cit. 



10 Rates of Runoff for the Designs of Conservation Structures, U.S. Soil Con- 

 servation Services, Tech. Pubs. 60-69, 1946-1948. 



