Manure application rather than plastic-film uncovering to sustainably alleviate plastic-greenhouse soil nitrate surplus and salinity in Yangtze River Delta

Despite leading global plastic-greenhouse production using soil culture, China’s low-to-medium-tech practices exacerbate soil nitrate surplus and salinity, deteriorating local environments. However, it remains uncertain how to sustain soil nitrate to achieve high production without environment penalty. This study conducted a field survey of plastic-greenhouse farms in Yangtze River Delta, and collected 107 questionnaires and 535 soil samples to comprehensively assess current status and remediation strategies of soil salinity. 40.5 %, and 68.2 % of soil samples exceeded the critical level of soil nitrate and electrical conductivity (EC) while nitrate and EC with or without Asparagus cultivation were median of 999 and 136 mg N kg−1, and 2809 and 659 µS cm−1, respectively, demonstrating severe nitrate surplus and salinity. Structural equation and random forest model demonstrated that soil salinity was related to greater inorganic nitrogen but lower manure input. Greenhouse uncovering decreased soil nitrate from 154 to 103 mg N kg−1 by 33.2 %, and soil EC from 706 to 562 µS cm−1 by 20.5 % but threatening surface water body. More manures decreased the ratio of soil nitrate-N to total N, and increased soil C/N counteracting the nitrate surplus in grape-cultivated soils. This study therefore recommends subsidizing manure applications in the cultivation of low-value crops and promoting the cultivation of high-value horticultural crops. This approach aims to prevent nutrient leaching caused by the removal of plastic film, thereby achieving the sustainable use of plastic greenhouse soils.