Zur Bedeutung der Bodenstruktur für den Ertrag von Zuckerrüben

Abstract

In the beginning of the 1990th a large-scale field trial with permanent plots on arable farms in southern and eastern Germany was established to determine the effect of various tillage systems [mouldboard ploughing (25-30 cm deep), conservation tillage with a rigid tine cultivator (10-15 cm and 20-25 cm deep), direct drilling] on yield, quality and economic performance of winter wheat and sugar beet crops. Winter wheat and sugar beet yield did not significantly differ between conservation tillage systems and ploughing, whereas, in both crops a yield loss occurred with direct drilling ( 4 % winter wheat and -15 % sugar beet). With regard to the net margin, lower production costs obtained with direct drilling compensated for the yield decrease in winter wheat but not in sugar beet. In 2003-2005 the effect of tillage treatments on soil chemical and physical properties and white sugar yield (WSY) was investigated to detect the reason for differences in yield reduction of tillage intensity significantly WSY. However, with conservation tillage and direct drilling concentration of soil organic carbon (Corg), soil nitrogen (Nt) and Corg/Nt-ratio increased in the upper layer of the topsoil, but remained unaffected in the lower topsoil and subsoil. Similarly, plant available P and K was accumulated in the upper topsoil, but K slightly decreased in lower topsoil horizon. Mg was not influenced by tillage treatments. This investigation showed that conservation tillage and direct drilling do not necessarily limit nutrient supply of crops compared to mouldboard ploughing. On the contrary, higher humus and nutrient concentrations found in the upper topsoil of several sites may indicate enhanced soil fertility and, moreover, improved conditions for plant growth with conservation tillage. Obviously, yield reduction in WSY going along with reduced tillage is caused by alterations of soil properties other than nutrient status. In contrast the investigation of soil structural parameters showed major differences between tillage systems. Decreasing tillage depth increased penetration resistance (PR) and dry bulk density (DBD), and diminished air filled pore volume (AFPV) in the topsoil down to 0.27 m depth, respectively. Several soil structural parameters were closely correlated with each other, and especially to WSY. Variation of single parameters explained up to 60 % of WSY variance attributed to tillage. Combining DBD from 0.03-0.07m depth, average PR from 0.03-0.27 m and AFPV from 0.03-0.18 m soil depth explained 77 % of the tillage effect. Nevertheless, multi-collinearity of soil physical parameters gave no clear evidence on cause and effect. Conclusively, this investigation clearly showed that conservation tillage systems may result in higher net margins. The production of winter wheat is even successful with no tillage but soil structure degradation due to direct drilling reduces WSY. Thus, sugar beet grown on loessial soils require mechanical loosening down to 0.15-0.20 m depth to produce high WSY and to obtain acceptable net margins. With regard to changing overall production conditions, especially raising production costs, conservation tillage can help maximizing net margins.