Status and Change in Chemical Properties of Polytunnel Soil in Korea from 2000 to 2012

Chemical properties of agricultural soils in Korea have been investigated at four-year interval in order of paddy, polytunnel, upland, and orchard soils since 1999; polytunnel soils were investigated over the whole country in 2000, 2004, 2008, and 2012. Polytunnel soils were taken from the surface (0-15 cm) and subsurface (15-30 cm) at 2,651, 1,274, 1,374 and 1,374 sites in all provinces of South Korea. One hundred sampling sites located in more than 400 m altitude were additionally investigated in 2008 and 2012. Average of soil chemical properties in 2012 except Jeju province were 6.6 for pH, 3.2 dS m-1 for EC, 37 g kg-1 for organic matter (OM), 1,049 mg kg-1 for available (Avail.) phosphate, 1.58 cmolc kg-1 for exchangeable (Exch.) K, 10.6 cmolc kg-1 for Exch. Ca, and 3.3 cmolc kg-1 for Exch. Mg. Except pH, averages of all chemical properties exceeded the upper limit of optimal range. The median values except pH showed a lower value than the averages. The pH, OM and Exch. Ca had slightly increased from 6.3 to 6.6, from 34 to 37 g kg-1, and from 7.7 in 2000 to 10.6 cmolc kg-1 in 2012, respectively. The order of sample ratios exceeding the optimal range were Avail. P2O5 (83%) Exch. Ca (80%) Exch. K (70%) Exch. Mg (65%) EC (55%) OM (48%) pH (29%) in 2012. The order of sample ratios below the optimal range was OM (25%) Exch. K (25%) pH (20%), Exch. Mg and Avail. P2O5 (9%) Exch. Ca (6%) in 2012. The excessive proportion of pH, Exch. Ca, Exch. Mg and OM slightly increased, while the insufficient proportion of those decreased. Approximately 55% of polytunnel soils exceeding EC 2 dS m-1 was evaluated with salt accumulated soils having the risk of growth disorder of crops. Nutrient contents in polytunnel soils in Korea showed high level especially Avail. P2O5 and Exch. cations. Therefore, recommended fertilization based on soil testing or plant testing is needed for soil nutrient management.