Aging of biochars under mediterranean climate conditions: a field study

Abstract

Biochar (BC) is the carbonaceous solid residue produced through the pyrolysis of organic residues with the objective to be used as soil ameliorants. Numerous research studies pointed out that BC can act as a soil conditioner enhancing plant growth by supplying and, more importantly, retaining nutrients and by improving soil physical and biological properties Lehmann and Joseph, 2015). In addition, the application of BC to soil is being proposed as a novel strategy to mitigate the emissions of carbon dioxide (CO2) to the atmosphere. Although BC is increasingly used as soil amendment and the properties of freshly produced BCs are well documented (De la Rosa et al., 2014) its biochemical stability and alteration during aging in the soil environment are still unclear (Ameloot et al., 2013). Therefore, we investigated the decomposition of BC and the changes of its characteristics during a 2-years field experiment under Mediterranean climate conditions. Here, five different BCs were mixed with a calcic Cambisol located at the experimental farm “La Hampa” (Coria del Río, Seville). Seeds of sunflower plants (Hellianthus annus) were planted and harvested after 5 months. After 6, 12 and 24 months soil samples were taken and biochar particles were carefully separated by hand. See further details of field conditions at Paneque et al, (2016). Biochar alterations were analyzed by measuring its elemental composition (C, N contents), pH, electrical conductivity (EC) and fragmentation degree. In addition, Field Emission Scanning Electron Microscopy (FESEM) and 13C Solid State Nuclear Magnetic Resonance (NMR) were used to assess biochar alterations. The biochemical recalcitrance of the BCs were assessed through a laboratory-based respiration experiment in which the BCs were mixed with soil and incubated for four months (25ºC, 60% water holding capacity) using an automatic respirometer.