Effect of biochar addition on soil respiration partitioning and root dynamics in an apple orchard.

Biochar addition to soil has been suggested as a promising strategy to increase soil carbon storage with important side-effects on soil fertility and crop productivity. Understanding the effect of biochar on soil respiration partitioning into rhizosphere-derived (Fr) and soil organic carbon-derived (Fsoc) components and on plant root dynamics and microbial activity is a crucial issue in the prediction of the impact of biochar on soil organic carbon and nutrient cycles. Within this framework, an experiment was carried out in an apple (Malus domestica Bork) orchard located in the experimental farm of the Bologna University (Italy). In spring 2009, 10 t of biochar per hectare were incorporated into the surface 20-cm soil layer by soil ploughing. The trenching method was used in order to partition total soil respiration (Fs) into Fr and Fsoc components in both biochar-treated and control soil. Soil respiration measurements were performed from June 2009 to March 2011. To study root dynamics, polycarbonate boxes were built and buried into the soil. Soil profile pictures were collected fortnightly with a CCD sensor scanner inserted in the boxes and analysed with the WinRHIZO Tron MF software. Biochar addition increased Fsoc and reduced Fr, even if the root length intensity (La) increased in biochar-treated soils relative to that in the control. A decrease in root metabolic activity was postulated to explain these contrasting results.