Technical note: Differences in the diurnal pattern of soil respiration under adjacent Miscanthus  ×  giganteus and barley crops reveal potential flaws in accepted sampling strategies

Abstract. For convenience, measurements used to compare soil respiration (R_s) from different land uses, crops or management practices are often made between 09:00 and 16:00 UTC, convenience which is justified by an implicit assumption that R_s is largely controlled by temperature. Three months of continuous data presented here show distinctly different diurnal patterns of R_s between barley (Hordeum vulgare) and Miscanthus  ×  giganteus (Miscanthus) grown on adjacent fields. Maximum R_s in barley occurred during the afternoon and correlated with soil temperature, whereas in Miscanthus after an initial early evening decline, R_s increased above the daily average during the night and in July maximum daily rates of R_s were seen at 22:00 and was significantly correlated with earlier levels of solar radiation, probably due to delays in translocation of recent photosynthate. Since the time of the daily mean R_s in Miscanthus occurred when R_s in the barley was 40 % greater than the daily mean, it is vital to select appropriate times to measure R_s especially if only single daily measurements are to be made.