FARM-N

Farm-N farm scale N model

The Farm-N farm-scale N model calculates a farm N surplus (N input to the farm - N exported in agricultural products) and then partitions this surplus between the various losses to the environment and changes in the amount of N stored in the soil.

The inputs of N to the farm that are recognised by the model are fertiliser, deposition of N from the atmosphere, fixation of N in crops, and imports of manure, animal feed, bedding and plant seed. The exports of N from the farm can be in the form of crop products (e.g. grain, straw), animal products (meat, milk) and exported manure. The losses of N that are modelled are ammonia volatilisation from animal housing, manure storage, excreta deposited in the field and field-applied fertiliser and manure, denitrification (dinitrogen and nitrous oxide emissions) from manure storage and soils, and nitrate leaching. The soil can be either a source or sink of N.

The information required from users includes the area and crop mixture for each rotation on the farm and the number and productivity of the livestock present and the type of animal housing used for those livestock. The model itself simulates the feed ration necessary to achieve the production indicated and how manure N is distributed between crops. The total amount of plant-available N applied to crops and the production of those crops follows the values used in the Danish manure and fertiliser regulation.

The losses of N to the environment are simulated using a range of methods that include the use of emission factors and empirical models. The change in soil N storage is simulated using a simple dynamic model.

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