Temporal variation in soil physical properties of paddy fields in Jeonnam province

Rice cultivation is so important that the rice paddy area of Jeollanam-do accounts for 21% of the rice paddy area nationwide. Therefore, scientific investigation and evaluation of the soil environment of agricultural land are needed for the stable production of agricultural products and conservation of agricultural environmental resources. This study was conducted to investigate the physical characteristics of rice paddy soil at 40 points in Jeollanam-do region in one cycle of 4 years (2015 - 2023) and to use it as basic data for sustainable agricultural soil maintenance. The soil physical property investigation includes plowing depth, bulk density, porosity, hardness, and organic matter content. The topography of 87.5% of the paddy soil in Jeollanam-do is valley/alluvial fan and river alluvium. The plowing depth tends to be highest in mountain foot. The bulk density of the sub-surface soil was highest in the river alluvium, and the hardness was also highest in the river alluvium. The organic matter content of topsoil and sub-surface soil showed the highest value in the fluvio-marine deposit and the lowest value in the river alluvium. The physical properties of the paddy soil by survey period tends to gradually improve after 2019. The bulk density of the topsoil continued to decrease, and the porosity tended to continuously increase. Organic matter in the topsoil decreased after 2015 and then slightly increased again, while organic matter in the sub-surface soil continued to increase. In addition, rice straw reduction and feed crop cultivation sites in paddy soils have increased since 2015. Therefore, it indicates that continuous organic matter supply is very important not only for soil physicality improvement but also for organic carbon storage.Soil physical properties of paddy soils by topography. Topography Soil layer PD1 (cm) BD2 (Mg m-3) Porosity (%) Sand (%) Silt (%) Clay (%) Hardness (mm) OM3 (g kg-1) Mountain foot TS4 17.3 (1.3) 1.24 (0.08) 53.3 (3.0) 37.2 (25.0) 41.5 (11.0) 21.3 (14.0) 28.9 (5.3) SS5 1.47 (0.05) 44.8 (1.7) 18.7 (4.1) 50.2 (5.7) 31.1 (8.0) 20.4 (0.7) 17.6 (7.8) Valley/ Alluvial fan TS 17.2 (2.1) 1.17 (0.02) 55.7 (0.8) 36.4 (2.6) 43.1 (3.2) 20.5 (3.7) 29.3 (1.9) SS 1.45 (0.10) 45.2 (3.7) 38.8 (3.2) 40.5 (5.9) 20.7 (3.6) 19.5 (3.5) 19.4 (4.8) River alluvium TS 16.6 (1.8) 1.16 (0.00) 56.3 (0.1) 40.3 (2.1) 41.9 (3.2) 17.8 (1.2) 28.9 (3.2) SS 1.50 (0.05) 43.5 (2.0) 39.7 (0.4) 41.6 (3.7) 18.8 (3.5) 21.0 (2.5) 17.5 (2.0) Fluvio-marine deposit TS 17.2 (2.1) 1.11 (0.11) 58.3 (3.9) 21.2 (4.6) 54.6 (5.6) 24.2 (1.2) 33.3 (3.0) SS 1.47 (0.13) 44.4 (4.8) 17.5 (9.8) 56.6 (2.7) 25.9 (7.6) 20.2 (1.5) 23.2 (11.6) Diluvial deposit TS 16.9 (3.0) 1.15 (0.07) 56.7 (2.6) 32.5 (3.0) 44.5 (5.1) 23.0 (2.1) 28.8 (4.0) SS 1.40 (0.14) 47.1 (5.2) 37.0 (3.0) 41.0 (4.4) 22.0 (7.3) 20.3 (2.9) 20.2 (10.6) 1PD, plowing depth; 2BD, bulk density; 3OM, organic matter; 4TS, topsoil; 5SS, sub-surface soil. Data are overall means (standard deviation) of survey points by topography in 2015, 2019, and 2023.