Accumulation of Miscanthus-derived carbon in soils in relation to soil depth and duration of land use under commercial farming conditions

Bioenergy is becoming an important option in Global Change mitigation policy world-wide. In agriculture, cultivation of energy crops for biodiesel, biogas, or bioethanol production received considerable attention in the past decades. Beyond this, the cultivation of Miscanthus, used as solid fuel for combustion, may lead to an increase in soil organic matter content compared to other agricultural land use, since C-sequestration potential in soils of Miscanthus crops is high due to, e.g., high amounts of harvest residues. This may indirectly contribute to a reduction of atmospheric CO2 concentration. The objective of the present work was to investigate the development of soil organic carbon and Miscanthus-derived C contents, as well as to estimate carbon stocks in soils cultivated with Miscanthus using 13C-natural-abundance technique. The investigations were carried out in relation to soil depth up to 150?cm in a sequence of 2, 5, and 16 y of cultivation relative to a reference soil cultivated with cereals. Amounts of total organic C (TOC) and Miscanthus-derived C (Miscanthus-C) increased with increasing duration of cultivation. For example, TOC increased from 12.8 to 21.3 g C?kg1 after 16 y of cultivation at the depth of 015?cm, whereby the portion of Miscanthus-C reached 5.8 g C?kg1. Also within deeper soil layers down to 60?cm depth a significant enhancement of Miscanthus-C was detectable even though TOC contents were not significantly enhanced. At soil depth below 60?cm, no significant differences between treatments were found for Miscanthus-C. Within 16 y of continuous commercial farming, Miscanthus stands accumulated a total of 17.7 Mg C ha1 derived from Miscanthus residues (C4-C), which is equivalent to 1.1 Mg C4-C ha1 y1. The annual surplus might function as CO2 credit within a greenhouse-gas balance. Moreover, the beneficial properties of Miscanthus cultivation combined with a low requirement on fertilization may justify the status of Miscanthus as a sustainable low-input bioenergy crop.