Reduced tillage is proposed as a method of C sequestration in agricultural soils. However, tillage effects on organic matter turnover are often contradictory and data are lacking on how tillage practices affect soil respiration in northern Europe. This field study (1) quantified the short-term effects of different tillage methods and timing on soil respiration and N mineralisation and (2) examined changes in aggregate size distribution due to different tillage operations and how these relate to soil respiration. The study was conducted on Swedish clay soil (Eutric Cambisol) and compared no-tillage with three forms of tillage applied in early or late autumn 2010: mouldboard ploughing to 20-22 cm and chisel ploughing to 12 or 5 cm depth. Soil respiration, soil temperature, gravimetric water content, mineral N and aggregate size distribution were measured. The results showed that respiration was significantly higher (P < 0.001) in no-till than in tilled plots during the 2 weeks following tillage in early September. Later tillage gave a similar trend but treatments did not differ significantly. Soil tillage and temperature explained 56 % of the variation in respiration. In the early tillage treatment, soil respiration decreased with tillage depth. Mineral N status was not affected by tillage treatment or timing. Soil water content did not differ significantly between tillage practices and therefore did not explain differences in respiration. The results indicate that conventional tillage in early autumn may reduce short-term soil respiration compared with chisel ploughing and no-till in clay soils in northern Europe.
