Long-term Assessment of Chemical Properties from Paddy Soils in Gyeongnam Province

Field monitoring was performed to evaluate the chemical properties of 260 paddy soils every 4 years from 1999 to 2015 in Gyeongnam province. Soil chemical properties, including soil pH, electrical conductivity, amount of organic matter (OM), available phosphate (<TEX>$P_2O_5$</TEX>), exchangeable potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na), and available silicate (<TEX>$SiO_2$</TEX>) were analyzed. In 2015, the average values of pH, OM, available <TEX>$P_2O_5$</TEX>, exchangeable K, Ca, and Mg, and available <TEX>$SiO_2$</TEX> was 5.8, <TEX>$30g\;kg^{-1}$</TEX>, <TEX>$222mg\;kg^{-1}$</TEX>, <TEX>$0.37cmol_c\;kg^{-1}$</TEX>, <TEX>$6.5cmol_c\;kg^{-1}$</TEX>, and <TEX>$1.4cmol_c\;kg^{-1}$</TEX>, <TEX>$252mg\;kg^{-1}$</TEX>, respectively. The frequency distribution within optimum range of paddy soils was 49.2%, 20.8%, 18.5%, and 5.8% for soil pH, OM, available <TEX>$P_2O_5$</TEX>, and available <TEX>$SiO_2$</TEX>, respectively. The available <TEX>$P_2O_5$</TEX> concentrations in 2015 was excess level with portion of 58% and did not alter significantly during the experimental period. Although the average of available <TEX>$SiO_2$</TEX> concentration has tended to increase with every year, the insufficient proportion of available <TEX>$SiO_2$</TEX> concentration in 2015 was 48%. These results indicated that a balanced management of soil chemical properties can properly control the amount of fertilizer applied for sustainable agriculture in paddy field.