Simulation of residual effects and nitrate leaching after incorporation of different ley types

Summary

The FASSET farm model was used to simulate production in an experiment where a grass-clover or a grass ley was either cut or grazed with dairy cows receiving low or high N sup-plements. The six different ley types were ploughed in and followed by three years with spring cereals with undersown catch crops.
The original model was extended with a new grass and clover model, which included the capability to simulate rhizodeposition and root growth. The new model predicted the observed annual carbon (C) and nitrogen (N) production satisfactorily. The simulated first year residual effects of a cut grass or grass-clover ley varied between 0 and 34, while the residual effect of a grazed grass or grass-clover ley varied between 71 and 150 fertilizer equivalents (kg N ha-1). Second and third year residual effects of the grazed leys were ca. 40 and 9 fertilizer equiva-lents, respectively, while the residual effects of the cut leys were ca. 5 and 3 fertilizer equiva-lents.
The effects of the different treatments on nitrate leaching were simulated quite satisfacto-rily. However, there was a deviation between the simulated and observed absolute level and timing of nitrate concentrations in suction cups. Scenario analysis showed that this partly could be explained by problems with refractory soil organic matter and gross nitrogen miner-alization in soils with high C:N ratios.