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 ($P_2O_5$), exchangeable potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na), and available silicate ($SiO_2$) were analyzed. In 2015, the average values of pH, OM, available $P_2O_5$, exchangeable K, Ca, and Mg, and available $SiO_2$ was 5.8, $30g\;kg^{-1}$, $222mg\;kg^{-1}$, $0.37cmol_c\;kg^{-1}$, $6.5cmol_c\;kg^{-1}$, and $1.4cmol_c\;kg^{-1}$, $252mg\;kg^{-1}$, 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 $P_2O_5$, and available $SiO_2$, respectively. The available $P_2O_5$ concentrations in 2015 was excess level with portion of 58% and did not alter significantly during the experimental period. Although the average of available $SiO_2$ concentration has tended to increase with every year, the insufficient proportion of available $SiO_2$ 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.