Influence of tillage on degradation kinetics using the litterbag method

A litterbag experiment was carried out in a tillage trial near Göttingen, Germany, comparing the long-term effects of mouldboard plough and rotary harrow on organic matter dynamics. The aim was to investigate the C loss and N balances in litterbags filled with N-poor, lignin-rich wheat straw and N-rich, lignin-poor maize residues, simulating the properties of green manures. The litterbags were buried at 0 and 5 and 15 and 20 cm depth and one fourth of them were removed after 3, 6, 9, and 12 months, respectively. The C loss rates, corrected for soil input into the litterbags, were significantly affected by tillage and bury depth and showed significant litter material x bury depth interactions. These were caused by generally higher C loss rates in the plough treatment, especially at 15 and 20 cm depth, and in the litterbags with maize residues. More soil was transferred to the litterbags in the plough treatment than in the rotary harrow treatment and more soil was found in the litterbags at 0 and 5 cm than at 15 and 20 cm depth. A smaller amount of stable aggregates in the surrounding soil is the most plausible explanation for this higher soil input. Nearly 40% of maize residue C was lost in the first three months from November to February, followed by a further exponentially decreasing loss of 40% over the next 9 months. Almost no wheat straw C was lost in the first three months, followed by a nearly linear loss of 60% over the next 9 months. The N balance showed strong N losses in the litterbags with maize residues for all exposure periods. In contrast, the N balance was always positive for wheat straw. The N balances, corrected for soil input, revealed significant bury depth effects and exposure period x bury depth interactions, but no significant tillage effects.