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DGT technique to assess P mobilization from greenhouse vegetable soils in China: A novel approach

Kalkhajeh, Yusef Kianpoor, Sørensen, Helle, Huang, Biao, Guan, Dong-Xing, Luo, Jun, Hu, Wenyou, Holm, Peter E., Hansen, Hans Christian Bruun
The Science of the total environment 2018 v.630 pp. 331-339
aluminum, eutrophication, greenhouses, leaching, losses from soil, oxalates, phosphorus, risk, soil properties, soil solution, soil types, surface water, topsoil, vegetable growing, vegetables, vegetation, China
Intensive phosphorus (P) inputs to plastic-covered greenhouse vegetable production (PGVP) in China has led to excessive soil P accumulation increasing the potential for leaching to surface waters. This study examined the mobility and hence the potential risk of P losses through correlations between soil solution P (PSol) and soil extractable P as determined by conventional soil P test methods (STPs) including degree of P saturations (DPSs), and diffusive gradient in thin-films (DGT P) technique. A total of 75 topsoil samples were chosen from five representative Chinese PGVPs covering a wide range of physiochemical soil properties and cultivation history. Total P and Olsen P contents varied from 260 to 4900, and 5 to 740mgkg−1, respectively, while PSol concentrations were between 0.01 and 10.8mgL−1 reflecting the large differences in vegetation history, fertilization schemes, and soil types. Overall, DGT P provided the best correlation with PSol (r2=0.97) demonstrating that DGT P is a versatile measure of P mobility regardless of soil type. Among the DPSs tested, oxalate extractable Al (DPSOx-Al) had the best correlation with PSol (r2=0.87). In the STP versus PSol relationships, STP break-points above which P mobilization increases steeply were 513μgL−1 and 190mgkg−1 for DGT P or Olsen P, respectively, corresponding to PSol concentration of 0.88mgL−1. However, for PSol concentration of 0.1mgL−1 that initiates eutrophication, the corresponding DGT P and Olsen P values were 27μgL−1 and 22mgkg−1, respectively. Over 80% of the investigated soils had DGT P and Olsen P above these values, and thus are at risk of P mobilization threatening receiving waters by eutrophication. This paper demonstrates that the DGT extracted P is a powerful measure for soluble P and hence for assessment of P mobility from a broad range of soil types.