Soil compaction variation during corn growing season under conservation tillage

• Difference between tillage methods for cone index was significant during growth season.
• Difference between tillage methods for bulk density was significant until fifth measurement.
• Both soil bulk density and cone index increased under zero tillage method.
• Soil bulk density and cone index were significantly affected by soil depth.
• Zero tillage slightly decreased corn yield compared to conventional method.

Area cultivated using conservation tillage methods has recently increased in Iran and soil compaction increment is one of the most challenging issues in this new technology. In addition to the soil compaction status at the end of growing season, soil compaction variation during the growing season is also important because of its potential effect on the crop growth and yield. Therefore, soil compaction variation during the corn growing season under different tillage methods and its effect on the crop yield was investigated in this study. The research was conducted in the form of a split plot experimental design with nine treatments and six replications. Main plots were tillage methods including: (1) conventional tillage method (CT); (2) reduced tillage (RT); and (3) zero tillage or direct drilling (ZT). Soil depth ranges of 0–0.10, 0.10–0.20, and 0.20–0.30 m were considered as sub plots. Soil bulk density (BD) and soil cone index (CI) were measured during corn growth season (eight measurements for bulk density and five measurements for cone index) as indices of soil compaction. Corn silage yield, thousand kernels weight, and grain yield were also determined in this research. Collected data were analyzed using SAS statistics software and Duncan's multiple range tests were used to compare the treatments means. Results indicated that tillage methods and soil depth had a significant effect on the soil bulk density so that the maximum soil bulk density was obtained from ZT method and soil depth range of 0.10–0.20 m. The difference between soil bulk densities in different tillage methods was statistically significant from the beginning of growth season to two month after the first irrigation (sixth measurement); while, this difference was not significant from the sixth measurement to the end of growth season. Soil cone index was also significantly affected by tillage methods and soil depth in such a way that ZT method and 0.20–0.30 m soil depth range had the maximum cone index. Although, the difference between tillage methods for corn yield and yield components was not statistically different, ZT method decreased corn thousand kernels weight, silage yield, and grain yield compared to the CT method for 11.1, 2.4, and 18.2%, respectively.