1. 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-35590 Saint-Gilles, France

2. 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

3. 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

4.  Weather data  Precipitation  Temperatures  Solar radiation Inputs

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

6.  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

7.  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

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

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

10. General Mineral N stock

11. General Mineral N stock

12. General Mineral N stock

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

14. 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 001 1 Number of animals*number of urine patches*2m² =0.01 0.99 20.020.98 30.030.97 40.040.96

15. General Mineral N stock

16. General Mineral N stock Urine affected Mineral N stock for 1st grazing …0…000 00… 000 00second grazing …0.03…0.030.020.01…0…00first grazing …0.96…0.970.980.99…1…11general pool Proportion of surface …x+2x+1x…21day of simulation

17. 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…0.990.980.97…0.96…0.9520.9440.936… first grazing00…0…0.010.020.03…0.03…0.03 … second grazing00…0…000 0.0080.0160.024… …00…0…000 000…

18. 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…0.990.980.97…0.96…0.9520.9440.936… first grazing00…0…0.010.020.03…0.03…0.03 … second grazing00…0…000 0.0080.0160.024… …00…0…000 000…

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

20. Water Reserve Leaching RainEvapotranspiration Soil Water Model:

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

22. 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.

23. Thank you