Status and Changes in Chemical Properties of Paddy Soil in Gangwon Province

Abstract

The chemical properties of paddy fields in Gangwon province were monitored every 4 years from 2003 to 2015 in order to provide basic information for soil fertility management of paddy fields. In 2015, the soil chemical properties of paddy fields were 5.9 in pH, <TEX>$22g\;kg^{-1}$</TEX> in organic matter (OM), and <TEX>$123mg\;kg^{-1}$</TEX> in available (Avail.) phosphate <TEX>$P_2O_5$</TEX>. Exchangeable (Exch.) potassium (K), calcium (Ca) and magnesium (Mg) were 0.39, 4.8 and <TEX>$0.9cmolc\;kg^{-1}$</TEX>, respectively, and Avail. <TEX>$SiO_2$</TEX> was <TEX>$170mg\;kg^{-1}$</TEX>. In the long-term analysis, the contents of Avail. <TEX>$SiO_2$</TEX>, Exch. K and pH of paddy soils showed increasing tendency. However, Avail. <TEX>$P_2O_5$</TEX>, Exch. Ca and Mg tended to decrease, and there were no significant changes in the contents of OM. Soil OM, Avail. <TEX>$P_2O_5$</TEX> and <TEX>$SiO_2$</TEX> were not different among the different topographical sampling sites. However, the mean value of Exch. K and Ca were different among the different topographical sampling sites, and exceeded optimal values in the fluvio-marine plains. Different soil texture resulted in different soil pH, while no difference for OM, Avail. <TEX>$P_2O_5$</TEX> and <TEX>$SiO_2$</TEX>. Paddy soil samples within appropriate pH range increased from 65% in 2003 to 77% in 2007, 68% in 2011, and 71% in 2015. In case of Avail. <TEX>$SiO_2$</TEX>, soil samples within appropriate range increased from 20% in 2003, to 37% in 2007, 29% in 2011, and 45% in 2015. Meanwhile, Cd and Pb were distributed to less than 5% of soil pollution standards. Cu, As and Zn were distributed to less than 10%, 15% and 20%, respectively. Therefore, paddy soil in Gangwon Province was judged to be safe. As a result, paddy fields with more or less in nutrient level need to be fertilized based on the soil analysis. And the application of silicate fertilizer is strongly recommended to those of paddy fields in need. In addition, soil management including the cultivation of green manure crop or application of rice straw is necessary to increase the organic matter content of paddy soil.