Changes in annual water quality index in April (left), July (center), and October (right).

The chemical properties of upland fields in Gyeonggi province were monitored every 4 years from 2001 to 2017 in order to provide basic information for soil fertility management of upland fields. In 2017, the soil chemical properties of upland fields were 6.3 in pH, 22 g kg -1 in organic matter (OM), and 651 mg kg -1 in available phosphate (Avail. P 2 O 5 ). Exchangeable (Exch.) potassium (K), calcium (Ca) and magnesium (Mg) were 0.83, 6.2 and 1.7 cmol c kg -1 , respectively, and electrical conductivity (EC) was 0.86 dS m -1 . In the long-term analysis, the contents of OM, Exch. Ca and pH of upland soils showed increasing tendency. However, the contents of Avail. P 2 O 5 tended to decrease, and there were no significant changes in the contents of Exch. K and EC. The optimal range of pH of upland fields changed to 45%