Soil and Water Conservation with Western Iowa Tillage Systems

ABSTRACT EXCESSIVE rates of surface run-off and erosion from the research watersheds at Treynor, Iowa, were measured during a 10-yr study of two contour-planted, watersheds cropped to corn. Low erosion rates occurred at a similarly cropped, level-terraced watershed and from a bromegrass watershed. These measurements show that level terraces and bromegrass are exceptionally effective conservation practices. But level terraces with point rows and irregular fields complicate farming and decrease farm machinery efficiency, and grass is not considered one of the more profitable crops for western Iowa loess soils. Mulch-tilled corn was also examined to assess its effect on surface runoff and soil loss. On one watershed, mulch tillage was used with parallel terraces (double normal spacing). The terrace-impounded water was removed by an underground drainage system, in-stalled in the spring of 1972. The contour-planted watersheds lost more soil than the mulch-tilled, parallel-terraced watershed in 1972. Only one storm produced erosion on the contour-planted watersheds, whereas the mulch-tilled watersheds had two erosion-producing storms. The 14.6 t/ha/yr (6.5 T/a/yr) of soil loss from the parallel-terraced, mulch-tilled watershed was unexpectedly large, but was partially caused by terrace failures during the May 5 storm, Soil loss was2.2 t/ha/yr (1.0 T/a/yr) in 1973, and surface runoff 8.4 cm (3.3 in.). The mulch-tilled watershed formerly in grass performed much as a grass watershed in 1972, with the lowest runoff and erosion values of all watersheds. It also performed well in 1973, probably reflecting the influence of prior grass management. The available data from the tillage system, started in 1972, are adequate to determine only the relative erosion control effectiveness.