Influence of biochar on drought tolerance of Chenopodium quinoa Willd and on soil-plant relations

The application of pyrogenic carbon, biochar, to agricultural soils is currently discussed as a win-win strategy to sequester carbon in soil, thus improving soil fertility and mitigate global warming. Our aim was to investigate if biochar may improve plant eco-physiological responses under sufficient water supply as well as moderate drought stress. A fully randomized greenhouse study was conducted with the pseudo-cereal Chenopodium quinoa Willd, using three levels of biochar addition (0, 100 and 200 t ha(-1)) to a sandy soil and two water treatments (60% and 20% of the water holding capacity of the control), investigating growth, water use efficiency, eco-physiological parameters and greenhouse gas (GHG) fluxes. Biochar application increased growth, drought tolerance and leaf-N- and water-use efficiency of quinoa despite larger plant-leaf areas. The plants growing in biochar-amended soil accumulated exactly the same amount of nitrogen in their larger leaf biomass than the control plants, causing significantly decreased leaf N-, proline- and chlorophyll-concentrations. In this regard, plant responses to biochar closely resembled those to elevated CO2. However, neither soil- nor plant-soil-respiration was higher in the larger plants, indicating less respiratory C losses per unit of biomass produced. Soil-N2O emissions were significantly reduced with biochar. The large application rate of 200 t ha(-1) biochar did not improve plant growth compared to 100 t ha(-1); hence an upper beneficial level exists. For quinoa grown in a sandy soil, biochar application might hence provide a win-win strategy for increased crop production, GHG emission mitigation and soil C sequestration.