Estimating Soil Properties and Rice Plant Growth in Liquefaction Paddy Land as Affected by Earthquake in Pohang City of Korea

Abstract

On 15th November 2017, an earthquake (magnitude 5.5) occurred at 36.10N and 129.37E on Pohang city in Korea. Due to the earthquake, liquefaction occurred in some agricultural lands of Yongcheon-ri, Heunghae-eup, Buk-gu, Pohang-si, Korea. This study investigated the physical and chemical properties of soil and liquefied sand and crop growth in the liquefaction site as affected by earthquake. The scale of liquefaction site in the experimental paddy was 30 - 50 cm ellipse, and most of the sand mixed with 14 - 22% of the gravel was piled up. The liquefaction scale was less than 0.01% of the area in each paddy land. The pH of the liquefied sand was a suitable property for rice cultivation, and heavy metal contents were lower than the concern level of soil environmental conservation act. As a result of comparing the liquefaction point (LP) and the around point 30 cm (AP) away from the LP, the partial cracked line was verified in the profile of LP. However, the soil structure maintained with the soil penetration resistance of 3 MPa or more. As the scale of sand liquefaction was small and the soil structure maintained, it considered that there was no problem in water and nutrient movement of soil and farming work. The effects of liquefaction on the growth and yield of rice were estimated to be insignificant because there was no statistically significant difference in plant height, stem height, panicle length, panicle number per fill, grain-filling rate, and yield of rice plants in the liquefaction site and control site. The soil penetration resistance of liquefaction sites in Pohang city. †L Site1, liquefaction site 1; L Site2, liquefaction site 2. ‡LP, liquefaction point in the liquefaction site; AP, around point 30 cm away from the liquefaction point.