Model application in small agricultural catchments Methods for calculation of leaching from agriculture and Effects of possible changes in agricultural practices Katarina Kyllmar Swedish University of Agricultural Sciences Division of Water Quality Management

Examples of factors influencing leaching Land useSoil types Crop distributionFertiliser levels

Simulation of nitrogen leaching from root-zone with the SOILNDB model

Information from each field concerning: –crop, fertiliser/manure application, yield, soil cultivation etc. for each year –soil type Climate data as daily values Data requirements Picture from Dynamic simulation of nitrogen leaching on field level with the SOILNDB model What is produced Time series of leaching for each field in the catchment Wheather conditions have large influence on annual leaching

Calculation of nitrogen leaching on field level with coefficients Leaching coefficients are calculated with the SOILNDB model Information concerning crop husbandry is based on official statistics The generated leaching coefficients are normalised for variations in weather between years The method is a further development of a method that was used for assessment of nitrogen load from arable land in Sweden Leaching coefficients Picture from Application of leaching coefficients Each field is given a coefficient based on field information

Normal leaching from root-zone on arable land in 1999

Leaching regions Plain districts in southern Götaland, Skåne Plain districts in southern Götaland, Halland Central districts in southern Götaland, Skåne Central districts in southern Götaland, Blekinge

Data requirements for calculation of leaching coefficients International soil classes Soil types Cultivation Climate Official agricultural statistics in production areas Crop distribution Fertiliser and manure as mean amounts for different crops including spreading periods for manure (autumn or spring) for these crops Standard yields for different crops Dates for soil cultivation, sowing and harvesting from practice when statistics is missing Leaching regions based on production areas Climate data in 20 year periods for each leaching region

Calculation of leaching coefficients Crops including applied fertiliser or/and manure are randomly put into climate series (20 years) according to occurrence in statistics The random procedure is repeated times which results in outcomes for each soil type and leaching region Crop rotations produced by random Simulation of nitrogen leaching with SOILNDB Each climate serie with randomised crop rotations are simulated Mean values are calculated for each combination of crop and following crop including fertiliser/manure application for these crops Some of the crops are put together into crop groups

The produced leaching coefficients are stored in a database Leaching region (4) Soil type (5) Crop (7) Crop, following year (5) Fertiliser/manure application (4) Fertiliser/manure, following year (4) Leaching coefficients could be chosen regarding to:

Example of leaching coefficients: Influence of soil type

Example of leaching coefficients: Effects of manure application

Application of leaching coefficients on nine monitoring catchments in south Sweden Calculations of nitrogen load in each catchment Basis for follow-up of environmental quality goals Scenarios for measurements in agricultural practices to reduce nitrogen leaching

Comparison between coefficient calculated leaching and measurements in stream outlets in two catchments

Measurements for reducing nitrogen leaching in the catchments  Spreading of manure in spring  Spring sown crops after termination of ley and fallow  Catch crop in spring cereals and spring rape  Catch crop in both winter and spring forms of cereals and rape  Winter cereals replaced by spring cereals and catch crop Nitrogen leaching was reduced from 34 to 54 % in the catchments

Nitrogen leaching from root-zone (kg/ha) Changes in nitrogen leaching after measurements in agriculture Initial leaching levels After measurements in agriculture

Coefficient method - Conclusions Large data basis and time consuming simulations for producing coefficients Simple to use the coefficients Effects on nitrogen leaching of changes in agricultural practices can easy be calculated New coefficients to describe effects of e.g. over-doses of fertiliser and variations in occasion of soil cultivation could be produced with additional simulations