Minimizing nitrogen environmental impacts in intensive greenhouse vegetable production systems in Shandong, China (NIVEP)

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Approx. 1/3 of all vegetables consumed in China are produced mostly by smallholders in so called solar greenhouses. However, farmers are overusing fertilizers, specifically N based fertilizers, and application rates >2000 kg N hectare and year in two growing seasons are rather normal and not the exception. This has caused and is causing tremendous environmental problems: soil acidification and salinization, degradation of soil ecological functions and increase occurrence of pathogens, accumulation of fungicides, pesticides and nitrates in top- and subsoils, nitrate pollution of groundwater, and increased losses of the greenhouse gas N2O. The overall objective of the project is the characterization and quantification of changes in plant and/ or microbial N removal, N immobilization processes and gaseous N losses for differently managed greenhouse soils as compared to conventionally managed arable soil. Thus, the project aims at the identification of feasible approaches for soil restoration and mitigation of soil hydrological and gaseous N losses from soils of intensively managed greenhouse vegetable production systems. Based on the overall objectives the following sub-objectives have been defined: 1) Quantification of the temporal dynamics of topsoil (0 to 1 m) and subsoil (1 to 3 m soil depth) changes in C and N stocks of solar greenhouse soils using a chronosequence approach. 2) Quantification of changes in actual and potential denitrification rates in soil profiles of intensively managed solar greenhouse vegetable system as affected by management and land use history. 3) Assessment of the effectiveness of anaerobic soil infestation and DOC additions to subsoils for removing excess NO3- from top- and subsoils. Thereby, tracing the fate of subsoil produced N2O for its possible contribution to soil-atmosphere N2O fluxes. 4) Identification of the potential of different solar greenhouse soil restoration measures and management methods such as biochar and/or straw application as well as drip irrigation for its effectiveness in increasing soil health, soil N retention potentials and NUE efficiency as well as reducing greenhouse gas emission and hydrological N losses from greenhouse vegetable production systems.