Soil pH increase under paddy in South Korea between 2000 and 2012

There is a growing body of knowledge on the spatial distribution of soil properties. Fewer studies have investigated temporal trends in soil properties whereas such information is essential for understanding soil productivity and long-term sustainability of agro-ecosystems. We have investigated temporal trends of soil chemical properties in paddy soils of South Korea using data from over two million topsoil samples (0-15 cm) from soil test laboratories collected between 2000 and 2012. The soil pH increased from 5.6 prior to 2000, to 5.9 after 2009, and the rate of increases was about 0.3 pH units per decade. Based on the confidence interval of spatial prediction, 35% of the paddy area (4180 km2) likely has a pH increase (likelihood >66%), and 20% (2350 km2) was very likely to have an increased soil pH (likelihood >90%). The rate of soil pH increase was higher in more acid soils. In addition to the soil pH increase, soil silicate (SiO2) content increased from a mean of 81 mg kg−1 prior 2000 to 153 mg kg−1 after 2009. This is the result of programs that recommend and subsidise the application of silicate fertilizers that has also caused higher levels of soil exchangeable Ca. The soil test data quantified soil changes over time and demonstrated the long-term effects of soil management on soil chemical properties, which is crucial to develop sustainable soil management systems.