Anna Jacobs

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 Corg) contents through the soil profile and on total soil Corg stocks (0–45 cm) was investigated at five different German sites. All sites showed similar results: after 10–13 years, soil Corg 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−1). Under ploughing, the soil Corg contents were distributed homogenously through the soil profile. Either mulching or direct drilling resulted in 3–28% higher soil Corg stocks than ploughing (49–116 t ha−1). 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 Corg 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.

Crop Rotational Effects on Yield Formation in Current Sugar Beet Production – Results From a Farm Survey and Field Trials

In Europe, the framework for sugar beet (Beta vulgaris L.) production was subject to considerable changes and for the future it is expected that sugar beet cultivation might concentrate around the sugar factories for economic reasons. Based on data from a national sugar beet farmers’ survey and multi-year crop rotation trials, the effects of cropping interval (number of years in between two subsequent sugar beet crops) and of preceding crops on sugar yield were elucidated under current Central European management conditions. The dominating sugar beet cropping interval was ≥4 years in the farm survey with pronounced differences between regions. However, the cropping intervals 2, 3, and ≥4 years did not affect the sugar yield. Therefore, significant differences in sugar yield between regions were assumed to be caused by multiple interactions between year, site, and farmers’ skills. Throughout Germany, the dominating preceding crops in sugar beet cultivation were winter wheat (Triticum aestivum L.) and winter barley (Hordeum vulgare L.). In the field trials, the sugar yield was 5% higher after pea (Pisum sativum L.) compared to maize (Zea mays L.) as preceding crop, while differences between the preceding crops pea and winter wheat, and wheat and maize were not significant. Repeated measurements of canopy development and leaf color during the growing season revealed a higher N-availability after pea as preceding crop. However, decreased growth after maize was not completely compensated for by high N-fertilizer doses. Overall, the causes for the differences in sugar yield between the preceding crops remained open. The results do not support concerns about substantial yield losses in sugar beet production due to a reduction in the cropping interval from 3 to 2 years. Nevertheless, short rotations with maize and sugar beet might increase the risk of Rhizoctonia solani crown and root rot infestation. Leguminous crops such as pea offer the potential for higher sugar beet yield with lower N-fertilizer doses.