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<br />cover. The rate of 1,700 Ibs per acre of total cover
<br />was equivalent to an increase of I inch per hour of
<br />water intake on soils of good structure, but 3,750 lbs
<br />per acre was required on soils of poor structure.
<br />
<br />If the soil surface was protected with straw in
<br />the amount of 2,5 tons per acre, the total intake of
<br />water by each soil tested was much higher than on
<br />the bare soil. The infiltration rates were also high and
<br />remained at relatively high levels throughout long
<br />periods of application, (Duley and Kelley, 1939),
<br />They also found that alfalfa gave a higher infiltration
<br />rate at the end of 90 minutes than oats, probably
<br />somewhat in proportion to the density of soil cover.
<br />The native sod absorbed water at about the same rate
<br />as the land covered with straw. However, where the
<br />grass was clipped close to the ground and the surface
<br />litter removed, the infiltration rate dropped almost as
<br />low as on cultivated land, Apparently the soil still
<br />containing the grass roots did not cause it to absorb
<br />water rapidly,
<br />
<br />Table 2 shows the difference in infiltration on
<br />soils of varying depth from deep to shallow, each
<br />having contrasting covers or land-use conditions. The
<br />soils are all silt loams, differing mainly in depth and
<br />content of organic matter. The Viola is a relatively
<br />shallow soil, comparatively low in organic matter
<br />content. The Muscatine is a deep, very dark colored
<br />soil, rich in organic matter content. Tama, Berwick,
<br />and Clinton are listed in the table in the approximate
<br />order of depth and organic matter content between
<br />Muscatine and Viola. The difference in land use is due
<br />mainly to plant cover. The bluegrass, of course,
<br />provides a dence surface cover highly protective
<br />against raindrop impact. The tests were made on
<br />farms where the grass was under practical grazing
<br />conditions. Corn is not noteworthy for any great
<br />protective effects, and intertillage tends to break
<br />down soil aggregation or crumb structure. Data in
<br />Table 2 are the results of replicated wet runs of the
<br />type-f infiltrometer under the 1,80 inches per hour
<br />
<br />simulated rainfall with a large drop size and an energy
<br />of impact similar to that of natural storms of this
<br />size, The results show: (1) the consistent and wide
<br />difference between the two kinds of land use (or
<br />plant cover) on each of the soils and (2) the steadily
<br />decreasing infiltration under a high protective cover
<br />such as bluegrass from the deep soil with high content
<br />of organic matter to the shallow soil with low content
<br />of organic matter. But this close relationship of
<br />infiltration to soil depth and content of organic
<br />matter is not found under the less protective corn,
<br />where surface conditions rather than soil depth and
<br />content of organic matter tend to govern intake. In
<br />other words, the differences in soil characteristics-
<br />even where they are rather large as in this case~have
<br />relatively little effect under adverse cover conditions.
<br />It is also interesting to note infiltration rates on the
<br />different soils during the last hour of this 5.hour
<br />storm during which a total of 9 inches of water was
<br />applied, As expected, the rates during the fifth hour
<br />are less than the average of the entire period. Without
<br />exception, the more protective cover on each soil is
<br />producing a greater infiltration rate as shown in Table
<br />2, Again it is readily seen that the soils tend to be
<br />arranged under the bluegrass in the order of their
<br />depth and content of organic matter. Under the less
<br />protective cover, however, soil differences tend to be
<br />oven;hadowed by what obviously happened on the
<br />soil surface, namely clogging of pores (Musgrave and
<br />Holtan, 1964).
<br />
<br />Woodward (1943) observed that infIltration
<br />rates increased directly with plant cover density
<br />although the magnitude of the increase varied be-
<br />tween cover types and soils. Mazruk, Kriz, and Ramig
<br />(1960) studied the rates of water entry as affected by
<br />age of perennial grass sods. In their study, two species
<br />of grass were used: Agropyron intermedium and
<br />Bromus inermis, Only the age of grass stand showed
<br />any significance in the rate of water entry in the soil,
<br />Box (1961) concluded that all vegetation improved
<br />water intake on the clay soil, but grass proved
<br />superior to brush, According to his study, under grass
<br />
<br />Table 2, InfIltration on soils of varying depth and organic matter with contrasting covers (after Holtan and
<br />Musgrave, 1947),
<br />
<br />SiItloam
<br />soils
<br />
<br />Total infIltration
<br />in 5 hour, inches
<br />
<br />Bluegrass
<br />Pasture
<br />
<br />Corn land
<br />
<br />Muscatine
<br />Tama
<br />Berwick
<br />Clinton
<br />Viola
<br />
<br />5.38
<br />5,03
<br />3A8
<br />2,77
<br />1.63
<br />
<br />134
<br />1.51
<br />L21
<br />2.17
<br />1.28
<br />
<br />Difference due
<br />to land use
<br />
<br />Infiltration rates
<br />during fifth hour
<br />
<br />Bluegrass
<br />in./hr
<br />
<br />Corn land
<br />in./hr
<br />
<br />4,04
<br />3.52
<br />2.27
<br />0,60
<br />0.35
<br />
<br />0,61
<br />0,77
<br />0.34
<br />0,29
<br />0,16
<br />
<br />0,11
<br />0,14
<br />0.12
<br />0,18
<br />0.08
<br />
<br />7
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