The use of a fertiliser allocation model for the evaluation of the impact of farm practices and policy measures on fertiliser use, nitrate residues and nitrate leaching

In the area of fertilisation, a large quantity of detailed information is available in Flanders, on one hand about farms, such as yearly production, use, transport and storage of manure and cultivated parcels, and on the other hand about agricultural parcels, such as yearly information on crops and applicable fertiliser standards, spatial information on size and location. However, information concerning fertilisation at parcel level is missing. In order to evaluate the impact of policy measures and farm practices at different levels (manure surpluses, nitrate residues and leaching, water quality,…), an educated estimate of the spatial distribution of fertiliser applications would be very useful. Therefore a fertiliser allocation model (BAM) has been developed in MS Access. Starting from the available information at farm and parcel level, BAM makes a reasoned estimate of the quantity and type of fertiliser that is applied on each parcel and of the time of application. BAM calculates for each fertiliser type (liquid or solid manure from cattle, pigs, poultry, compost, mineral fertilisers,…) the total amount used per farm and per year and assigns it to the agricultural parcels of each farm, taking into account the crops, the corresponding fertilisation standards and expert knowledge of common farming practices. The fertilisation doses calculated by BAM were validated using data of parcels of the derogation monitoring network which is followed up by the Soil Service of Belgium (Vandervelpen et al., 2011). The results showed that the applied manure types were, in general, estimated correctly. On average, the N-fertilisation doses estimated by BAM were slightly lower than the fertilisation declared by the farmers. The P-fertilisation doses were, on average, estimated more or less correctly. This validation proved that BAM can be used for scenario analysis. In a next step, BAM has been used to evaluate the effects of different farm practices and policy measures in an extensive scenario study on fertiliser use in Flanders. Reference Vandervelpen D., Van Overtveld K., Tits M., Peeters L., Elsen A., Van de Vreken Ph., Bries J., Batelaan O., Van Orshoven J., Vanderborght J., Diels J., Vandendriessche H. (2011) Establishment and follow-up of a monitoring network of farms to assess the impact of derogation on the water quality. Study carried out under the authority of the Flemish Land Agency by the Soil Service of Belgium and the Department of Earth and Environmental Science (K.U.Leuven). ca. 204 pp.