Overseer models decomposition of all organic material by separating it into inorganic and organic fractions.
Modelling of the inorganic fraction is similar to fertiliser in that it is added to the soil mineral N pool in the month the material is applied to the soil.
Decomposition of the organic fraction is based on the N content of the organic fraction, and other factors such as temperature, soil moisture, and cultivation practice. The N released by decomposition is added to the soil mineral N pool. Hence there is no fixed rate of release, and for low organic N materials, the release may occur over more than one year.
Thus the impact of adding organic material on N leaching depends on the rate N is released from the organic matter, the inputs and removals of other sources of N, and soil characteristics such as the amount of drainage.
Organic materials can be added in the Fertiliser input tab in OverseerFM. All N in ‘Composts/mulches’ are assumed to be in the organic fraction, whereas for 'Other organic materials', the total N content and 'Percentage of N in inorganic form' must be specified. Refer to Entering fertiliser and nutrients different ways for further information - Creating a Farm analysis -> Fertiliser