Soil pH increase under paddy in South Korea between 2000 and 2012 Budiman Minasny a, *, Suk Young Hong b , Alfred E. Hartemink c , Yoo Hak Kim c , Seong Soo Kang c a School of Life & Environmental Sciences, Faculty of Agriculture and Environment, The University of Sydney, NSW 2006, Australia b National Institute of Agricultural Sciences, Rural Development Administration (RDA), Wanju-gun, Jeollabuk-do 55365, Republic of Korea c University of Wisconsin—Madison, Department of Soil Science, FD Hole Soils Lab, 1525 Observatory Drive, Madison, WI 53706, USA A R T I C L E I N F O Article history: Received 27 August 2015 Received in revised form 22 January 2016 Accepted 27 January 2016 Available online xxx Keywords: Rice Silica pH increase Acidity Soil databases Slag silicate fertilizer A B S T R A C T 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 km 2 ) likely has a pH increase (likelihood >66%), and 20% (2350 km 2 ) 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 (SiO 2 ) 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. ã 2016 Elsevier B.V. All rights reserved. 1. Introduction Soil has a central role in the global challenges, including food and fibre production, freshwater provision, biodiversity conserva- tion, greenhouse gases buffer, energy sustainability, and ecosystem services provision (McBratney et al., 2014). There is a need to maintain and improve soil resources in order to cope with these global challenges. Soil conditions are highly dynamic and soil changes can be accelerated by climate change and anthropogenic influences. The ever-growing human population has put pressure on soil resources. Agricultural production and soil condition are linked through, for example, soil carbon levels, soil erosion, acidification, salinization, and soil nutrient imbalances. An important change is soil acidification due to agricultural activities, which has been reported to occur worldwide and it is mostly attributed to the use N fertilizers (Barak et al., 1997; Guo et al., 2010; Marchant et al., 2015). To ensure the security of our soil resources and to better understand anthropogenic impacts on soils, it is essential to monitor soil conditions and assess soil changes. Quantifying and understanding the direction of soil change is crucial for sustaining food production (Reynolds et al., 2013). The variation of soil properties at a national scale has been assessed and quantified through digital soil mapping (Arrouays et al., 2014). Most studies focus on a single soil property, e.g. mapping of soil carbon, soil pH, or available water capacity (Hong et al., 2013; Mulder et al., 2016). Very few studies have quantified temporal changes in soil properties at a national scale (Kirk et al., 2010) whereas such studies may reveal the effects of soil management and assist in the development of sustainable agricultural systems. Understanding soil change as a response to anthropogenic and global environment effect may provide a better understanding of the storage of carbon and nutrients, mobilization of nutrients from reserves and transformation, and gas exchange between soil and atmosphere (Reynolds et al., 2013). Previous work demonstrated the use of legacy soil data from soil surveys to study temporal trends at regional or national extents (Lindert et al., 1996; Hartemink, 2006). Another unique * Corresponding author. E-mail address: budiman.minasny@sydney.edu.au (B. Minasny). http://dx.doi.org/10.1016/j.agee.2016.01.042 0167-8809/ ã 2016 Elsevier B.V. All rights reserved. Agriculture, Ecosystems and Environment 221 (2016) 205–213 Contents lists available at ScienceDirect Agriculture, Ecosystems and Environment journal homepage: www.elsev ier.com/locate /agee