Per Abrahamsen

Daisy: an open soil-crop-atmosphere system model

Abstract Daisy is a well tested dynamic model for simulation of water and nitrogen dynamics and crop growth in agro-ecosystems. The model aims at simulating water balance, nitrogen balance and losses, development in soil organic matter and crop growth and production in crop rotations under alternate management strategies. The software, which recently was rewritten, has been carefully designed to facilitate interaction with other models, either by replacing individual Daisy processes or by using Daisy as a part of a larger system, thus making Daisy an open software system.

Dual permeability soil water dynamics and water uptake by roots in irrigated potato fields

Water movement and uptake by roots in a drip-irrigated potato field was studied by combining field experiments, outputs of numerical simulations and summary results of an EU project (www.fertorganic.org). Detailed measurements of soil suction and weather conditions in the Bohemo-Moravian highland made it possible to derive improved estimates of some parameters for the dual permeability model S1D_DUAL. A reasonably good agreement between the measured and the estimated soil hydraulic properties was obtained. The measured root zone depths were near to those obtained by inverse simulation with S1D _DUAL and to a boundary curve approximation. The measured and S1D _DUAL-simulated soil water pressure heads were comparable with those achieved by simulations with the Daisy model. During dry spells, the measured pressure heads tended to be higher than the simulated ones. In general, the former oscillated between the simulated values for soil matrix and those for the preferential flow (PF) domain. Irrigation facilitated deep seepage after rain events. We conclude that several parallel soil moisture sensors are needed for adequate irrigation control. The sensors cannot detect the time when the irrigation should be stopped.

Integrated modelling of crop production and nitrate leaching with the Daisy model.

Graphical abstract

Comparison of simulated water, nitrate, and bromide transport using a Hooghoudt‐based and a dynamic drainage model

For large-scale hydrological modeling, the accuracy of the models used is a trade-off with the computational requirements. The models that perform well on the daily/meter scale may not perform well when applied at the yearly/kilometer scale. We compare two models of water flow and nitrate and bromide transport in a tile drained soil. The first model is based on a 2-D grid with an explicit drain node, here called the Dynamic Drainage Model (DDM). The second and less computationally expensive model is based on an 1-D vertical discretization where the horizontal flow is included as a sink term based on the Hooghoudt theory, here called the Hooghoudt Drainage Model (HDM). Both are based on Finite Volume Method solutions to Richards equation and to the advection-dispersion equation (ADE), and embedded within the Daisy agroecological model, which includes the nitrogen cycle. The two models are run with 10 years of weather data and three different lower-boundary conditions. Losses of water, nitrogen, and bromide to both drain pipes and deep percolation/leaching are compared between the models, at daily and yearly time scales. In no case do we find the discrepancy large enough to warrant a rejection of the use of the faster HDM instead of DDM. For the daily time scale, we find in general a higher Nash-Sutcliffe efficiency coefficient for water (0.98–1.00) than for nitrate (0.97–1.00), and the lowest for bromide (0.95–1.00). The results are explained with a low concentration gradient along the water flow pathway toward the drain.