Water discharge and nutrient leaching from organic mixed crop rotation

Summary

Water discharge and nutrient leaching studies were conducted in an experimental field under organic farming practice for 20 years. The water discharge measurements cover five years out of a six-year crop rotation. The water discharge for the whole year was 1520 m³/ha (=152 mm). More than 2/3 of the total discharge occurred in April-May. The total precipitation for the whole year was 680 mm.
The total amount of N in the drainage runoff was 11.5 kg/ha and the flow-weighted average content 7.5 mg/l. The total amount of P in the drainage runoff was 48 g/ha and the flow-weighted average content 0.031 mg/l. 85 % of the total P was dissolved reactive phosphorus (DPR).
Some preliminary correlation between N leaching and N management was observed, i.e. higher N concentrations in drainage water were found on green fallow after autumn ploughing compared to first-year grass or spring cereal. Variation in the P concentration of the drainage water between the plots seems to be correlated to soil P status rather than P management.