P. Schweigert* and R.R. van der Ploeg Institute of Soil Science, University of Hannover,

1. Monitoringsoil mineral nitrogen concentration in Germany: Preliminary resultsand some methodical challenges P. Schweigert* and R.R. van der Ploeg Institute of Soil Science, University of Hannover, Hannover, Germany

2. N surplus of agricultural landin Germany

3. Consequences of N surplus • Soil mineral nitrogen increased

4. Consequences of N surplus • Soil mineral nitrogen increased • Nitrate leaching increased

5. Consequences of N surplus • Soil mineral nitrogen increased • Nitrate leaching increased • Nitrate concentration in groundwater often increased over 50 mg l-1 • Problem for drinking water supliers, because: 50 mg l-1 is the upper limit in drinking water

6. Consequences of N surplus • Soil mineral nitrogen increased • Nitrate leaching increased • Nitrate concentration in groundwater often increased over 50 mg l-1 • Problem for drinking water supliers, because: 50 mg l-1 is the upper limit in drinking water 80 % of the drinking water comes from groundwater

7. Measures to reduce nitrate leaching • Prevention of overfertilization • Promotion of cover crop cultivation during fall

8. Result check: Monitoring programs • In drinking water catchments • Soil mineral nitrogen (NO3-N) in 0-90 cm depth • In fall before leaching begins

9. Result check: Monitoring programs Baden-Württemberg:- Since 1987- First program in Germany- 60000 samples per year

10. Trend ofsoil mineral nitrogen in Baden-Württemberg

11. Trend ofsoil mineral nitrogen in Baden-Württemberg

12. Trend ofsoil mineral nitrogen in Baden-Württemberg

13. Preliminary result - Soil nitrate concentration decreases- Nitrate leaching probably decreases

14. Methodical challenges? Are there still problems, that should be solved? Are there anyhow methodical challenges?

15. Trend ofsoil mineral nitrogen in Baden-Wuerttemberg

16. Trend ofsoil mineral nitrogen in Baden-Wuerttemberg

17. Methodical challenge: Quantification of the influences of the weather on the mineral N content of the soils

18. Result check: Monitoring programs Liebenau- Since 1992- 100 samples per year

19. Soil mineral nitrogen in Liebenau

20. Soil mineral nitrogen and the precipitation until sampling date

21. Soil mineral nitrogen and the precipitation until sampling date

22. Soil mineral nitrogen and the precipitation until sampling date

23. Soil mineral nitrogen and the precipitation until sampling date

24. Soil mineral nitrogen and the precipitation until sampling date

25. Soil mineral nitrogen as a function of precipitation until sampling date

26. Soil mineral nitrogen as a function of precipitation until sampling date

27. Simple regression with 1 variable NO3-N = - 0.15P10 + 66.7 r2 = 0.46* NO3-N = mean NO3-N fall content of all soils (kg ha-1), 0-90 cm depth P10 = Precipitation since 1. October, until date of sampling (mm)

28. NO3-N = - 0.15P10 + 66.7 r2 = 0.46*

29. NO3-N = - 0.15P10 + 66.7 r2 = 0.46*

30. NO3-N = - 0.15P10 + 66.7 r2 = 0.46*

31. Multiple regression with 2 variables NO3-N = - 0.20P10- 2.8 Y + 86.6 r r2 = 0.86 *** NO3-N = mean NO3-N fall content of all soils (kg ha-1), 0-90 cm depth P10 = Precipitation since 1. October, until date of sampling (mm) Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend

32. Multiple regression with 2 variables NO3-N = - 0.20P10 - 2.8 Y + 86.6 r2 = 0.86 *** NO3-N = mean NO3-N fall content of all soils (kg ha-1), 0-90 cm depth P10 = Precipitation since 1. October, until date of sampling (mm) Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend

33. NO3-N = - 0.20P10 - 2.8 Y + 86.6 r2 = 0.86 ***

34. Multiple regression with 4 variables NO3-N = - 0.17P10 - 3.2 Y - 0.08 P9 + 3.1 T10 + 52.3 r2 = 0.97 *** NO3-N = mean NO3-N fall content of all soils (kg ha-1), 0-90 cm depth Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend P10 = Precipitation since 1. October until date of sampling (mm) P9 = Precipitation of September (mm) T10 = Mean air temperature at 2 p.m. in October (° C)

35. Multiple regression with 4 variables NO3-N = - 0.17P10 - 3.2 Y - 0.08 P9 + 3.1 T10 + 52.3 r2 = 0.97 *** NO3-N = mean NO3-N fall content of all soils (kg ha-1), 0-90 cm depth Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend P10 = Precipitation since 1. October until date of sampling (mm) P9 = Precipitation of September (mm) T10 = Mean air temperature at 2 p.m. in October (° C)

36. Multiple regression with 4 variables NO3-N = - 0.17P10- 3.2 Y- 0.08 P9 + 3.1 T10 + 52.3 r2 = 0.97 *** NO3-N = mean NO3-N fall content of all soils (kg ha-1), 0-90 cm depth Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend P10 = Precipitation since 1. October until date of sampling (mm) P9 = Precipitation of September (mm) T10 = Mean air temperature at 2 p.m. in October (° C)

37. NO3-N = - 0.17P10 - 3.2 Y - 0.08 P9 + 3.1 T10 + 52.3 r2 = 0.97 ***

38. Decrease of nitrate in groundwater

39. Conclusions Preliminary results: - Measures to reduce the nitrate leaching are successful

40. Conclusions Methodical challenge: - Values of soil nitrate are superimposed by atmospheric influences

41. Conclusions Methodical challenge: - Values of soil nitrate are superimposed by atmospheric influences - Multiple regression models can detect these influences