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

Subject Area Ecology of Land Use
Soil Sciences
Term from 2018 to 2022
Project identifier Deutsche Forschungsgemeinschaft (DFG) - Project number 391878289
 
Final Report Year 2022

Final Report Abstract

Approximately 1/3 of vegetables in China are produced in solar greenhouses. Most farmers use conventional irrigation with over fertilization (CIF), thereby applying approximately 2000 kg N ha^-1 fertilizer over two cropping seasons per year. In the project NIVEP (Minimizing nitrogen environmental impacts in intensive greenhouse vegetable production systems in Shandong, China), we quantified environmental N losses by leaching (organic and inorganic N compounds) or due to gaseous emissions (in the form of the greenhouse gas N2O, but as well in the form of N2) for different greenhouse vegetable production management systems. Our results show, that N leaching losses for standard farmers practice (over-fertilization and flood irrigation) often exceed 400 kg N ha^-1 yr^-1 and that N2O emissions may be as high as 50-70 kg N ha^-1 yr^-1. These are enormous losses of reactive N compounds which are extremely damaging for the environment due to effects on water climate or on the climate systems. Moreover, N2 production by denitrification may as well be about 250-450 kg N ha^-1 yr^-1. Considering N2 (and N2O) production by denitrification in combination with observed N leaching losses and plant N uptake allowed us to show that most of the applied organic and inorganic fertilizers is lost to the environment (about 80-90%) and not taken up by the crop. This is highly alarming and calls for a revision of current management schemes applied for vegetable production in solar greenhouses in China. Specific attention should be given to the period of anaerobic soil disinfection (ASD). ASD is currently developing to a standard practice to combat soil born diseases, specifically nematodes. ASD is usually applied every 2-3 years during the summer fallow period and has so far not been considered regarding its importance as a period of major N losses to the environment. Our experiment shows, that N losses during the ASD period are gigantic and often higher as during the crop growing period. This huge environmental N losses may only be reduced if farmers stop to apply chicken manure to the soil for priming ASD. This is unnecessary and counterproductive as incorporation of residues with a wide C:N ratio (and not of chicken manure) is a very effective measure to promote long-term soil anaerobiosis (about 14 days) and helps as well to remove access soil N by denitrification (mainly as N2) and to rebalance nutrients in the soil. Overall, we found alarming evidence that soil health is at risk in solar greenhouse vegetable production systems in China, e.g. manifested by extremely high soil N concentrations, major nutrient imbalances (e.g. N:P:K ratios, soils may not need P and K fertilizer applications for years), but not by high heavy metal concentrations. This calls for rapid adaptations of the production systems, specifically, it is recommended to consider large scale introduction of drip fertigation, reduction of rates of fertilizer applications, while increasing rates of residue and biochar incorporation in soils, which will lead to increasing soil carbon stocks and increasing retention capacity of the soil for nutrients.

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