Epsilon Archive for Student Projects

Abstract

Phosphorus (P) losses from agricultural fields have been recognised as one of the most
important sources of P causing eutrophication in water bodies. Water transport in soil plays
an important role in P leaching from drained fields. In this study, the ICECREAM model was
employed to simulate 15-year drainage and P leaching from a sandy loam soil at the Mellby
experimental site in south-western Sweden. The results were compared with measured data in
order to test the applicability of the model at the Mellby site, identify important processes
controlling drainage and P leaching at Mellby, and suggest potential future improvements to
the model to better suit the Mellby soil.

Sensitivity analysis showed that parameters related to soil physical properties (soil texture,
soil porosity, field capacity, wilting point and saturated conductivity), infiltration capacity
(CN2) in connection with field management practices and macropore flow moderately or
significantly affected the total amount of drainage. These parameters also indirectly affected
P leaching, which was closely correlated to drainage. Soluble P leaching was also greatly
sensitive to base saturation, while particle P leaching was greatly affected by parameters
related to particle generation for macropore transport (detachability and particle extraction
depth).

The model accurately simulated total drainage and drainage dynamics for the 15-year study
period when the drainage partition coefficients for deep percolation (K1 and K2) and the
parameters related to macropore flow (tresh_watin and frac) were calibrated. The simulation
showed that considerable amounts of drainage water (17%) bypassed tile drains and that
water was able to move very fast along preferential flow paths in this sandy soil.

The model accurately simulated the transport dynamics of soluble PO4
3--P and total P, but
failed to simulate total amounts and concentrations. Leaching of both soluble P and total P
was overestimated. One clear conclusion from this work was that new parameters are greatly
needed in the model to better describe sorption-desorption processes for P to Fe-oxides or
(and) Al-oxides in the soil. This would allow P leaching from a soil like this to be simulated
with higher precision. It was also concluded that parameters related to particle generation
need careful calibration in future simulations.

The simulations for the Mellby site showed that when the soil P pools were large, it was
difficult to distinguish the effects of reduced P fertilisation on leaching. They also showed
that management practices such as crop type, tillage practices, etc. can influence P losses.
The model should be further tested on field data to determine the accuracy of such
estimations.