Nitrogen mineralisation dynamics of meat bone meal and cattle manure as affected by the application of softwood chip biochar in soil

We studied the impact of added biochar on the N mineralisation dynamics of two organic fertilisers by incubating loamy sand soil for 133 days in controlled conditions. Biochar made from softwood chips was added to soil at 0, 4.6, 9.1 and 13.6 g kg(-1) soil dry matter (DM) either alone, or in combination with meat bone meal (MBM) and composted cattle manure (CCM) fertilisers. Soil mineral N concentration was determined on days 0, 14, 28, 56, 84 and 133. Net N mineralisation in the MBM treatment was much larger than in the CCM or the unfertilised treatments. Constant soil moisture during the incubation provided suitable aerobic soil conditions for nitrification: after day 14, soil mineral N was dominated by nitrate in all treatments. Biochar additions decreased the mineral N concentrations in all treatments, probably because of immobilisation by microbes. In unfertilised soil, the immobilisation by biochar increased steadily with application rate and time, but in the MBM and CCM treatments, it started to decrease or level off after two months, possibly due to the turnover of microbial biomass. The main biochar-induced impacts on soil N mineralisation dynamics could be modelled by using standard and confined exponential models.