A model of soil nitrogen reserves in an Irish grass sward C. Paillette 1, 2, D. Hennessy 1, L. Delaby 3, D. O Connor 2 and L. Shalloo 1 1 Animal & Grassland Research and Innovation Centre, Teagasc, Moorepark, Fermoy, Co. Cork; 2 Cork Institute of Technology, Bishopstown, Cork; 3 INRA, AgroCampus Ouest, UMR 1348, PEGASE, F Saint-Gilles, France

Introduction:  Grass growth highly variable within and between years  Factor influencing grass growth  Soil type  Climatic conditions  Management  Soil reserves of nutrients  Nitrogen  Water  Models as management tools  Soil reserves influenced by  Environmental factors  Sward management

Objectives  Develop a dynamic model to predict  Organic nitrogen reserves  Mineral nitrogen reserves  Water reserves  Depending on  Weather  Management of the farm  Stocking density and timing of grazing  Timing and quantity of fertilizer

 Weather data  Precipitation  Temperatures  Solar radiation Inputs

 Weather data  Precipitation  Temperatures  Solar radiation  Soil type  Composition  Water Holding Capacity Inputs

 Weather data  Precipitation  Temperatures  Solar radiation  Soil type  Composition  Water Holding Capacity  Management data  Dates of grazing and stocking rate  Timing and quantity of fertilization Inputs

 Weather data  Precipitation  Temperatures  Solar radiation  Soil type  Composition  Water Holding Capacity  Management data  Dates of grazing and stocking rate  Timing and quantity of fertilization  Grass quantity Inputs

Model development:  Relationships are derived from the existing literature  Two sub models  Soil N reserves  Organic N  Mineral N  Water reserves

Organic N Stock Mineral N Stock Soil N model (1)

General Mineral N stock

General Mineral N stock

General Mineral N stock

General mineral N stock Urine affected Mineral N stock for first grazing Urine N deposition

General Mineral N stock Urine affected Mineral N stock for first grazing Urine N deposition Day of rotation Proportion of surface affected Urine affected mineral pool General mineral pool Number of animals*number of urine patches*2m² =

General Mineral N stock

General Mineral N stock Urine affected Mineral N stock for 1st grazing …0…000 00… second grazing …0.03… …0…00first grazing …0.96… …1…11general pool Proportion of surface …x+2x+1x…21day of simulation

General Mineral N stock Urine affected Mineral N stock for 1st grazing Urine affected Mineral N stock for 2 nd grazing day of simulation12…xx+1x+2…yy+1y+2… Proportion of surface general pool11…1… …0.96… … first grazing00…0… …0.03…0.03 … second grazing00…0… … …00…0… …

Urine affected Mineral N stock for 2 nd grazing Urine affected Mineral N stock for 1st grazing General Mineral N stock … day of simulation12…xx+1x+2…yy+1y+2… Proportion of surface general pool11…1… …0.96… … first grazing00…0… …0.03…0.03 … second grazing00…0… … …00…0… …

Organic N Stock Mineral N Stock Vegetation Grass GrowthAbscission Loss to the atmosphere Leaching Fertilization Soil N model (2)

Water Reserve Leaching RainEvapotranspiration Soil Water Model:

Outputs  Daily  Organic nitrogen reserve  Mineral nitrogen reserve  Nitrogen leached

Conclusion:  This work shows that reserves of nutrients in the soil can be modelled  This model  Uses equations extracted from different models that have proven accurate for Irish conditions  Combines them to get a comprehensive model.  Future work will be to link to a grass growth model to  Take into account the effect of nitrogen availability on grass growth  Modulate the grass uptake of nitrogen.

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