1. Determination of the Subsoil Compaction Risk of Agricultural Soils in The Netherlands Jan van den Akker

2. Introduction Subsoil compaction: ploughpan Wheel load carrying capacity Example Terra Tire carrying capacity map of The Netherlands Dutch Soil Database: statistical prediction subsoil compaction Conclusions

3. Definition of subsoil TOPSOIL PLOUGH PAN SUBSOIL

4. Subsoil compaction is (partly) irreversible RiskEffect Recovery topsoil-- - -+ ploughpan0 / -- - subsoil0 / ---

5. Development of BD in time

6. Wheel load carrying capacity

7. Compaction by compression and shear

8. Wheel load carrying capacity

9. Wheel load: Stress propagation in soil

10. Input SOCOMO and preconditions Terra Tire 73x44.00-32 (width = 1.1 m; outer diameter = 1.86 m contact area = 0.513 m 2 ) Parabolic stress distribution in tire-soil contact area Vertical and horizontal load (5% of vertical) Concentration factor = 4 Ploughing depth sand, loam and clay soil is 25, 30 and 35 cm Rut depth = 3 cm Tire inflation pressure: as low as tire load allows Bulk density subsoil (plough pan) = max according threshold value => strength optimal Soil moisture condition: pF 2.5 = 30 kPa = - 300 cm H2O Precompression stresses, cohesion and angle of internal friction calculated with pedotransfer functions of Lebert and Horn (1991)

11. Subsoil Strength at soil water suction = 300 hPa (pF 2.5)

12. Precompression stress of Dutch subsoils (pF 2.5)

13. Terra Tire, sandy soil, wheel load 80 kN (8 tonnes)

14. Subsoil Strength and Maximal allowable wheel load Terra Tire (pF 2.5)

15. Max wheel load (kN) - Terra Tyre - Subsoil - pF 2.5

16. Dutch Soil Database: BD upper subsoil

17. Dutch Soil Database: Frequency BD upper subsoil

18. Dutch Soil Database: Predicted subsoil overcompaction in 2010

19. Carrying capacity Terra Tire  Overcompaction count

20. Precompression stress  Overcompaction count

21. Soil Quality MIDDLE

22. Soil Quality HEADEND

23. Conclusions Soil strength determines the susceptibility of subsoils to compaction. More soil strength data is needed. Pedotransfer functions on soil strength must be developed. The carrying capacity can be calculated rather easy. A good estimation of ground pressure distribution is required. Maps with the carrying capacity show the problem and possibilities The carrying capacity concept is a sound basis for recommendations However, the calculated wheel loads might be too low Therefore DYNAMIC soil strength properties are needed And need to include RESILIENCE of soils to compaction.