The Effect of Crop Residue Percentages and Their Chopped Size on Soil Compactibility

The advancement of technology and increasing use of mechanization in agriculture, as well as increasing size of agricultural machinery for farm capacity improvement, have led to soil compaction. In developed countries, various reports of the soil compaction impacts on the reduction of agricultural products have been provided. In developing countries, soil compaction represents a less-known issue and a its destructive nature in agriculture has not been sufficiently addressed. Furthermore, in developed countries, the soil is rich in organic matter due to conservation tillage; however, in Iran, conservation tillage is not possible to perform because of traditional agriculture and using old agricultural machinery. Therefore, plant residues are either removed from fields, or burned. However, sufficient content of organic matter in field can contribute to soil compaction mitigation. The aim of this study was to investigate the effect of percentage of crop residues and their size on soil compaction at different soil moisture contents. For these purposes, five different soil moisture contents (8, 10, 12, 14 and 16% based on dry soil weight) and 4 residue rates at 3 fragmentation sizes were observed in terms of soil compaction. At all different soil moisture contents and residue sizes, with increasing percentage of added straw to the soil, the soil displacement increased. Moreover, as the straw size increased, the initial displacement during compression decreased, e.g., the maximum displacements for straw percentage of 12% and soil moisture of 8% were 64, 62 and 60 mm considering the straw sizes of 1, 2.5 and 5 cm, respectively. With high residue percentage, the final soil density and soil compaction were lower due to the low specific density of straw relative to soil. Furthermore, with high percentage of straw, more deformations and displacements were occurred in the mixture due to large deformation of straws. The density changes of soil-straw mixture were more significant at high residue percentages.