EROSION EFFECTS ON SOIL-WATER STORAGE, PLANT WATER-UPTAKE, AND CORN GROWTH

Many investigators have suggested that the greatest negative effect of erosion on soil productivity is the decrease in available water-holding capacity, but few have attempted to evaluate this relation directly. In this 4-yr study, we evaluated the effects of past erosion on soil water storage, plant water uptake, and corn (Zea mays L.) growth on a linear slope of Dubuque silt loam soil (fine-silty, mixed, mesic Typic Hapludalf) in southwestern Wisconsin. Levels of past erosion were based on depth to red clay (2Bt horizon): slight, 0.95 m; moderate, 0.74 m; and severe, 0.45 m. The total quantity of plant-extractable water that could be stored in the upper 1 m of slightly eroded soil (181 mm) was 7% more than that for moderately eroded soil (169 mm) and 14% more than that for severely eroded soil (159 mm). For all erosion levels, water retained in the 0.5- to 1.0-m soil depth was utilized by corn. Erosion level had no negative effect on early-season plant growth. As plant-extractable water decreased to < 55 to 60% of total, evapotranspiration (ET) and vegetative-growth rates decreased as erosion level increased. The greatest differences in ET rates among erosion levels were observed during a 35-d period in the drought year of 1988 when rates averaged 3.7 mm d-1 for slight erosion, 2.6 mm d-1 for moderate erosion, and 2.2 mm d-1 for severe erosion. For the 3 yr in which plant water stress was observed, maximum plant heights for the slight erosion level averaged 7% mom than those for moderate erosion and 13% more than those for severe erosion. Although the soil's capacity to store and supply water decreased as erosion increased, the observed effects of erosion level on grain and stover yields, grain-yield components, and harvest populations typically were not significant.