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subsoil gave a correlation coefficient of 0.54; surface organic matter, 0.50; clay content of the subsoil, OA2; and organic matter in the subsoil, OAO, When the factors were combined in multiple correlations, the highest multiple coefficlent of 0,71 was obtained with noncapillary porosity, organic matter of both surface and subsoil, and clay content of the subsoil. Effect of frost Frozen ground affects infiltration. If frozen when very dry, some soils are fluffed up and frost is discontinuous, as in the honeycomb and stalactite types. A soil under this condition may be permeable as, or even more permeable than, frost-free soil. On the other hand, if the soil is frozen while saturated, concrete frost in the form of a very dense, nearly impermeable layer often results, Trimble et a1. (1958) found that in the Northeast, infiltration was zero on concrete frost in the open and forest area, but was not affected where soil was traversed by large holes in which water had not frozen, Infiltration tests on concrete frost in northern Minnesota forest and grassland gave 0.09 in./hr of infiltration rate in silt.]oam soils and OA7 in./hr in sands (Stoeckeler and Weitzman, ] 960), Effect of plant cover Musgrave and Holtan (1964) have stated that vegetation is one of the most significant factors affecting surface entry of water. Vegetation or mulch protects the soil surface from rainfall impact. Massive plant root systems such as grass in sods perforate the soil, keeping it unconsolidated and porous, The organic matter from crops promotes a crumb struc. ture and improves permeability, On the other hand, vegetation such as a row crop gives less protection from raindrop impact, depending upon the stage of growth, and the root system perforates only small portions of the soil profile and the normal accompanying tillage may further reduce perme. ability, Forest litter, crop residues, and other humus materials protect the soil surface, High biotic activity in and beneath surface l,ayers opens up the soil, resulting in high entrance capacities. Hays (1949) showed the general trend ofresults obtained at three latitudes in the central U.S, by comparing runoff amounts from continuous row crops, crops in 3-year rotations, and continuous grass, At the Upper Mississippi Valley Conservation Experi. ment Station, La Crosse, Wisconsin, for instance, it was found that average annual runoff on Fayette silt loam with a slope of 16 percent was 27,7 percent of rain fail for continuous corn (row crop); 20,6 percent for corn in rotation of corn-barley-red clover; 18.9 percent for barley in the rotation; 11.5 percent for red clover in the rotation; and 5.5 percent for protected bluegrass, Similar comparisons for the Red Plains Conservation Experiment Station, Guthrie, Oklahoma, and the Missouri Valley Loess Conserva- tion Experiment Station, Clarinda, Iowa, were re- ported (G]ymph and Holtan, 1969), It is evident that runoff from these plots is inversely related to the density of vegetation and the frequency of cultiva- tion, The density of herbaceous vegetation is closely related to infiltration, as has been attested by several studies on the western range, Packer (195]), for instance, found that the percent of the soil covered by living or dead plant parts was closely related to runoff, and therefore to infiltration. As cover density increased to about 70 percent on wheatgrass and cheatg~ass areas, overland flow decreased. At densities above 70 percent, there was little further decrease. Fibrous-rooted vegetation such as wheatgrass has been found to be much more effective in controlling runoff than taprooted annual weeds (Lull, 1964). The great influence of vegetated cover on infiltration is further evidenced by the fact that bare.soil infiltration capacity can be increased 3 to 7.5 times with good permanent forest or grass cover, but little or no increase results with poor row crops (Jens and McPherson, ] 964). Duley and Kelley (1939) considered that there might be far greater variations between the infiltra- tion rates obtained under different surface conditions on a single soil type than on different soil types having the same surface condition, This consideration may make it necessary to study the infiltration rate characteristic of surface conditions rather than that of a specific soil type, Although plant cover is like all other factors that affect inf1ltration and runoff, it is not an independent factor. Rauzi and Fly (1968) found that in general water intake rate increased with vegetal cover, and that this increase was about 1 inch per hour per 2,000 Ibs per acre vegetal cover with good soil structure, and I inch per hour per 3,200 lbs per acre with poor soil structure. A large number of tests on the silty range site enabled the separation of rates of water intake of three major soil structure classes, The amount of vegetal cover required to increase the rate of water intake I inch per hour for the silty range site was between 1,000 and 5,000 Ibs per acre, At the 3,000 lbs per acre level of vegetal cover, the mean water intake rates were for excellent structure, 2AO inches per hour; for fair to good structure, 1.65 inches per hour; and for poor structure, 1.10 inches per hour. The clayey range site included soil textures of sandy clay loam, silty clay loam, and clay. Water intake increased rapidly when the vegetal cover increased to between 500 and 3,000 lbs per acre, No increase in water intake and even a slight decrease was noted with more than 4,000 lbs per acre of total 6