SIZE DISTRIBUTION OF SEDIMENT IN RILL RUNOFF IN RESPONSE TO VARIATIONS IN-GROUND COVER, FREEZING, SLOPE AND COMPACTION OF A FINE SANDY LOAM

Fine sandy loam was subjected to laboratory simulated rill flow at two slopes (3·5% and 7%) to test the effects of incorporated straw, surface compaction and diurnal freezing-and-thawing cycles on sediment size distribution (six size grades between 600 and <38 μm) in rill runoff using soil troughs of 3·66 m length. Sediment mass of all size grades was six to 34 times greater from bare surfaces than from surfaces with incorporated straw. Freezing-and-thawing gave 22% to 47% more mass of <106 μm grades than without freezing. Freezing-and-thawing increased the mass of grades <53 μm (by 34 to 74%) from bare surfaces but not from surfaces with straw. The slope of 7% yielded 120 to 150% more mass of all sediment grades than did the 3·5% slope. Uncompacted surfaces yielded 15 to 40% more mass of all grades than did the compacted surfaces, mostly affecting the coarsest grade from the compacted surfaces. The effects of ground cover, freezing and slope were greatest on the finest size grade. Ground cover consistently interacted significantly with slope, temperature treatment and compaction to nullify erosive effects on bare soil. © 1993 Silsoe Research Institute.