MECHANICAL EFFECTS OF INCORPORATED RESIDUES AND MULCH ON SOIL EROSION BY WATER
Abstract
The importance of crop residues in reducing soil erosion by water has been extensively reported. The mechanical effect of crop residues on reducing erosion is most noticeable from seedbed preparation to full crop canopy, and it is almost exclusively related to the percentage of soil surface cover. Residue mixing into the few inches of the soil surface is a common feature of conservation tillage systems. With the development of erosion theory, new approaches have been made available to describe the mechanical effects of crop residues on soil erosion by water. An experiment was conducted at the Purdue Agronomy Farm, near Lafayette, Indiana, on residue incorporation: depth (7.5 and 15 cm) and residue rate (0, 1 and 4 ton/ha), and incorporation versus loose mulch on the surface (0, 20 and 45% soil coverage). Wheat straw was incorporated with a tototiller into field plots on a Russell silt loam soil, with 4.4% slope. Rainfall was simulated with a programmable rainfall simulator and longer slope length than 35 ft was simulated with added inflow. Surface roughness, residue cover, soil moisture, runoff rates, sediment concentration, flow velocity, and eroded aggregate sizes were measured. Rill and interrill contributions to the erosion rates and mulch failure parameters were estimated. Residue cover percent was found to be the most important factor in the effectiveness of residues in reducing erosion. Incorporated residues reduced mulch susceptibility to be carried away and helped to maintain the initial residue cover throughout a storm. Soil loss ratio (SLR) residue cover (RC) relationships, reported in the form SLR=ae('-bRC), were found to have values of b equal to -0.028, with slight change of b values for anchored residues. A greater difference in a values was found in anchored compared to unanchored residues. The value of b, when soil loss is related to residue cover as a mulch factor, was found to be -0.036. Mulch failure occurred for all treatments. The most resistant treatment measured in terms of Manning's n due to mulch, shear stress due to mulch and slope length at failure, was 0.053 kg/m('2)/cm of residues incorporated at 7.5 cm depth with a residue cover percentage of 45%.
Degree
Ph.D.
Subject Area
Agronomy
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