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.
An electromagnetic measurement with GEM‒2 was examined as a simple and rapid method for measuring soil electrical conductivity （EC） in tsu-nami‒inundated farmlands. The apparent soil electrical conductivity （ECa） ascertained using GEM‒2 was too high according to the increase in the application rate of potassium chloride in a pseudo‒seawater inundated field of which the EC had been adjusted using potassi-um chloride spraying. Furthermore, results for ECa were correlated with those obtained using a soil EC sensor. These results showed that differences in ECa values were obtainable through nondestructive and noncontact sensing with GEM‒2 in tsunami‒inundated farmland. The overlying contour plot measured using GEM‒2 on the map, such as Google Earth, was able to easily provide more information about the relation be-tween ECa and terrain condition. Measuring ranges in the depth direction according to the GEM‒2 measure-ment at 80 kHz frequency were regarded as affecting all layers from the fi eld surface to at least 1 m below without limited to only the fi eld surface. We can com-pare EC1:5 and ECa by using the soil EC sensor to-gether with GEM‒2, thereby rapidly investigate for salt leaching while working in tsunami‒inundated farmlands.
A decontamination method is urgently needed for agricultural lands contaminated with radio-active cesium during the accident at the Fukushima Daiichi Nuclear Power Plant in March 2011. As an ex-perimental site, we selected a paddy fi eld in Iitate Vil-lage, which is in the planned evacuation zone. Prelimi-nary testing showed that 95 % of the radioactive cesium exists within the top 2.5 cm of uncultivated ag-ricultural soil. The cesium was primarily adsorbed with finer fractions of the soil, such as soil particles or aggregates smaller than 0.02 mm Stokes diameter. On the basis of these results, we proposed an experimen-tal method of paddy decontamination by puddling a thin layer of topsoil under flooded conditions and draining the suspended soil particles. We carried out a test on the method using a plastic container (38.0 cm× 53.0 cm × 26.5 cm) before using the method on the paddy field. The process reduced the concentration of radioactive cesium. An important advantage of the technique is that it generates less waste than the method of removal of top soil.