Relation of Field-Plot Runoff to Management and Physical Factors
1966
Wischmeier, W. H.
The detailed data for runoff analysis were assembled from nearly all erosion plot studies in the United States. Individual study averages of runoff from cropped plots have ranged from 3% to 36% of total precipitation, from 1 to 14 inches annually. Analyses indicted factor relations valuable for predicting water yields from cropland areas. Improved soil and crop management reduced average plot runoff about 40%. An inverse, curvilinear relation of runoff from growing and maturing corn (Zea mays L.) to crop yield was highly significant. At moderate fertility level, runoff reduction by contour tillage averaged slightly more than 15%. Under natural field conditions, runoff from row crops averaged a 10% increase for each additional percent slope. The relationship is expressed by: log W = 0.521 + .041s, where W is inches runoff and s is percent slope. Slope effect decreases as the surface becomes smooth and approaches zero for dense meadow or saturated soils. Effect of slope length on annual runoff was usually insignificant, but some transmission losses in the growing season and acquisitions in the dormant season were indicated. For 35 fallow soils with sand contents ranging from 4% to 66%, runoff was inversely proportional to organic matter content but was little affected by differences in particle size distribution.
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