Monitoring and modelling of water and heat fluxes from asparagus fields

Precise estimates of evapotranspiration and other scalar fluxes of asparagus (Asparagus officinalis) crops are required for irrigation control, regional water budget projections or climate impact modelling studies. In Germany, asparagus fields are frequently quite extensive and enable the application of eddy covariance (EC) technique to measure the turbulent fluxes of CO(2), sensible and latent heat (H(2)O) and momentum. In this work we present results of two year EC measurements (2015-16) over an extended asparagus field with commonly used cultivars ('Backlim' and 'Grolim'). With supplementary collected seasonal data of fern area, fern height and several meteorological sensors combined with a sophisticated quality assessment and footprint analysis we are able to parameterize well established physical and physiological crop responses. These include the aerodynamic resistance with separate transfer terms above and within the canopy and the bulk stomatal resistance in a one-layer setting of energy balance formulation. The instantaneous fern canopy conductance is predicted by partial responses of photosynthetic active radiation and fern area, air temperature, air vapour pressure deficit, fern senescence state and the daily canopy to air temperature difference.