Soil organic carbon as affected by direct drilling and mulching in sugar beet - wheat rotations

The effect of conventional ploughing, mulching, and direct drilling on the soil organic C (soil C-org) contents through the soil profile and on total soil C-org stocks (0–45 cm) was investigated at five different German sites. All sites showed similar results: after 10–13 years, soil C-org contents in the surface soil (0–10 cm) were 15–71% and 33–42% higher under direct drilling and mulching, respectively, than under ploughing (8–18 g/kg). Under ploughing, the soil C-org contents were distributed homogenously through the soil profile. Either mulching or direct drilling resulted in 3–28% higher soil C-org stocks than ploughing (49–116 t/ha). However, the tillage management was no significant factor since the sites showed the effects to different extents but were the mathematical replications. Five to six years later, trends and values were similar. We concluded that the main effect of mulching or direct drilling was the stratification with higher soil C-org contents in the surface soil. Since this is a positive means for soil protection, we suggested that the use of mulching or direct drilling can contribute to a sustainable soil management in crop rotations with sugar beet which are characterized by a strong physical impact on the soil during harvest.