Effect of tillage speed and straw length on soil and straw movement by a sweep

Abstract

Crop residue cover protects soil from erosion caused by water and wind. High amounts of residue are not needed and part of crop residue needs to be removed by bailing and part of the crop residue needs to be incorporated into soil. Since tillage operation impacts crop residue cover, cover residue management has been integrated into tillage operations. To provide mathematical relationships between tillage operation and residue coverage, thoroughly understanding the relationship between tillage tool, soil, and crop residue, and to develop mathematical models are important. Therefore, detailed data of soil, crop residue, and tillage tool interactions are needed. It is very difficult to acquire these data in field tests due to too many uncontrollable variables. Soil bin experiments were conducted to study soil and crop residue movement and crop residue incorporation by tillage with a sweep. Cereal straw was selected to represent surface crop residue, and there was no crop residues in the soil bin soil. The length of the straw ranged from 50 to 250 mm with an increment of 25 mm. A 325-mm-wide sweep was operated at speeds of 5, 7.5, and 10 km h −1 with a constant depth of 100 mm. Aluminum cubes of 1 cm 3 were used as point tracers to measure surface soil displacement; straw pieces with specific lengths were previously colored and used as point tracers to measure straw displacement. Straw tracers were oriented as parallel and perpendicular to the tool travel direction. Straw displacements measured with two different orientations of straw tracers were not significantly different. The straw mixtures of different lengths were spread over the soil surface to cover those tracers, and the straw mixtures worked well in studying straw movement and incorporation as two facts: (a) they reduced number of plots and then reduced experimental time and (b) they could represent single-sized straw in studying straw incorporation. Research results indicated that higher tillage speed resulted in larger soil and straw displacement that also buried more straw. Straw displacement increased with increasing straw length. The forward straw displacement increased by 20% when straw length increased from 50 to 250 mm although this increase was not statistical significant. The forward soil displacement was reduced by 70% and greater if tillage speed was reduced from 10 to 5 km h −1 independent of the straw length. The width of soil disturbance was increased by 40% if increasing tillage speed from 5 to 10 km h −1. Results showed that longer straw were less buried than shorter straw at the same tillage speed. Compared to that of 50-mm-long straw, the unburied percent of 250-mm straw increased by 75% at 10 km h −1 speed, 85% at 7.5 km h −1, and 90% at 5 km h −1. For all nine lengths of the straw, the unburied straw percent in mass was ranged from 45 to 85% when tillage speed was 5 km h −1; and it was reduced to 25–40% if tillage speed increased to 10 km h −1.