Abstract
In converted paddy fields, a hard soil crust can affect soybean seedling emergence. This study used surface soil from converted paddy fields to inves-tigate the relationship between the emergence of soy-bean seedlings and crust strength, and the effects of particle size distribution and soil organic matter on hard crust formation. When crust strength（as mea-sured by a crust hardness meter）≥ 10 mm（0.35 MPa），emergence of seedling soybeans was less than 60 %. Where the clay content ≥ 0.20 kg kg－1, silt≥0.30 kg kg－1, and sand < 0.50 kg kg－1, many crust strengths ≥ 10 mm. However, for sand contents < 0.50 kg kg－ 1, if the igni-tion loss ≥ 0.13kg kg－ 1, and the total carbon content ≥ 0.06 kg kg－ 1, the crust strength of all samples de-creased to less than 10 mm. These results indicate that the crust strength decreased with increasing ignition loss and total carbon content suggesting that soil or-ganic matter, including bulky organic matter, was the main contributor to aggregate stability, causing less close packing, and cohesion of soil particles, thus re-ducing soil crust strength.
