Model predicts nitrate leaching from drained fields

When a field is artificially drained it also increases the risk for leaching of nutrients such as nitrogen (N) and phosphorous. Leaching of nitrate imposes a risk for the recipient waterbodies: rivers, lakes, and coastal waters.

Field N balance

In one of her studies, Saghar K. Motarjemi and colleagues from Aarhus University and Geological Survey of Denmark and Greenland (GEUS) developed a model to assess how much of the applied N fertiliser is prone to leaching through the drainage systems, as well as what happens to the field N balance.

Since 1999 the Danish Pesticide Leaching Assessment Programme (PLAP) has, on behalf of the Danish Government, provided results on risk of leaching. The high-quality data collected by the PLAP provided the basis for this study.

Also read: How to balance draining fields with holding onto nitrogen

Using the agroecological DAISY model, the researchers were able to assess the risk of N leaching through the drainage system. The DAISY model takes into account the atmosphere, plants, soil, and water, which are the fundamental components of an agricultural system incorporated into one model.

The model simulated nitrate leaching through drainage-systems and the crop N uptake with a high accuracy, which could result in rough approximations on other N balance components that are difficult to measure in reality.

11% of N input leached

“Based on the simulations by the model, on an annual average over the 10 years, 70% of the N input was utilized by the crops, 11% was leached to the groundwater, 9% was leached through the drainage system, while 7% was lost through e.g. denitrification,” Saghar K. Motarjemi explains.

The scientists conclude there is a need for improved management practices to reduce the nitrate levels in the drainage-water in tile drained agricultural fields.