1. Monitoring soil mineral nitrogen concentration in Germany: Preliminary results and 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 land in Germany

3. Soil mineral nitrogen increased Consequences of N surplus

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

5. 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 Consequences of N surplus

6. 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 Consequences of N surplus

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

8. In drinking water catchments Soil mineral nitrogen (NO 3 -N) in 0-90 cm depth In fall before leaching begins Result check: Monitoring programs

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

10. Trend of soil mineral nitrogen in Baden-Württemberg

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

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

15. Trend of soil mineral nitrogen in Baden-Wuerttemberg

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

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

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

27. Simple regression with 1 variable NO 3 -N = mean NO 3 -N fall content of all soils (kg ha -1 ), 0-90 cm depth P 10 = Precipitation since 1. October, until date of sampling (mm) NO 3 -N = - 0.15 P 10 + 66.7 r 2 = 0.46 *

31. Multiple regression with 2 variables NO 3 -N = mean NO 3 -N fall content of all soils (kg ha -1 ), 0-90 cm depth P 10 = Precipitation since 1. October, until date of sampling (mm) Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend NO 3 -N = - 0.20 P 10 - 2.8 Y + 86.6 r r 2 = 0.86 ***

32. Multiple regression with 2 variables NO 3 -N = mean NO 3 -N fall content of all soils (kg ha -1 ), 0-90 cm depth P 10 = Precipitation since 1. October, until date of sampling (mm) Y = Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend NO 3 -N = - 0.20 P 10 - 2.8 Y + 86.6 r 2 = 0.86 ***

34. Multiple regression with 4 variables NO 3 -N= mean NO 3 -N fall content of all soils (kg ha -1 ), 0-90 cm depth Y= Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend P 10 = Precipitation since 1. October until date of sampling (mm) P 9 = Precipitation of September (mm) T 10 = Mean air temperature at 2 p.m. in October (° C) NO 3 -N = - 0.17 P 10 - 3.2 Y - 0.08 P 9 + 3.1 T 10 + 52.3 r 2 = 0.97 ***

35. Multiple regression with 4 variables NO 3 -N= mean NO 3 -N fall content of all soils (kg ha -1 ), 0-90 cm depth Y= Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend P 10 = Precipitation since 1. October until date of sampling (mm) P 9 = Precipitation of September (mm) T 10 = Mean air temperature at 2 p.m. in October (° C) NO 3 -N = - 0.17 P 10 - 3.2 Y - 0.08 P 9 + 3.1 T 10 + 52.3 r 2 = 0.97 ***

36. Multiple regression with 4 variables NO 3 -N= mean NO 3 -N fall content of all soils (kg ha -1 ), 0-90 cm depth Y= Year (1992 = 0; 1993 = 1; 1994 = 2; etc.), temporal trend P 10 = Precipitation since 1. October until date of sampling (mm) P 9 = Precipitation of September (mm) T 10 = Mean air temperature at 2 p.m. in October (° C) NO 3 -N = - 0.17 P 10 - 3.2 Y - 0.08 P 9 + 3.1 T 10 + 52.3 r 2 = 0.97 ***

38. Decrease of nitrate in groundwater

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

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

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