Plastic shed soil salinity in China: Current status and next steps

ABSTRACT Plastic sheds are widely used for vegetable production in China, which accounts for ca. 80% cultivation area of plastic-shed vegetable globally. However, the current soil sustainability in plastic sheds in China is severely threatened by soil salinization. Here, we analysed in a meta-analytic study the soil salinity and fertility of 15,739 plastic sheds in China from 234 articles. When compared to open field soils nearby, soils in plastic sheds were greatly salinized as indicated by the concentration of total soluble salts of 2.43 g kg-1 and percent changes (the ratios in percent of values in plastic shed soils to those of open field soils - 100%) of either total soluble salts or electrical conductance (EC) of 141.1%. The concentration of total soluble salts in Yangtze River Basin were 3.08 g kg-1 greatest salinized among all five regions of China with North China and Bohai Rim being the least salt-affected region (1.84 g kg-1) but greatest percent change of soil organic matter (68.5%). Soil soluble salts were 5.76 g kg-1 in top 0-10 cm indicating the greater salt stress in the surface soils. Percent changes of NO3- and K+ were 264.8% and 224.3% being the two greatest increments among eight salt ions. The top five soluble salt components in percent were NO3- > SO42- > Ca2+ > Cl- > Na+ in mass base (84.0% in total). The special microclimates, and chemical and organic fertilization largely contributed to current soil salinization. We recommend the use of following critical practices for improving soil sustainability in plastic sheds: (1) limit the use of fertilizers containing residual salts (2) top dressing of highly soluble nutrients rather than base chemical fertilization (3) to assimilate NO3- or SO42- by plants and microorganisms and water leaching of Cl- and Na+; (4) the use of organic amendments. Future studies should attach more importance to these practices, and investigate the underlying mechanisms to achieve sustainable soil management and vegetable production for the smallholder farmers.