Interaction of pyrolysed and un-pyrolysed organic materials enhances carbon accumulation in soil irrigated with water of variable electrical conductivity

Abstract Long-term effects of applying pyrolysed [biochar (BC)] or un-pyrolysed [rice straw (RS) and farmyard manure (FYM)] organic materials individually or their co-application on soil irrigated with saline water (SW) is not well known. An incubation study was conducted for 52 weeks with soil collected from plots irrigated with water of variable electrical conductivity (EC) [SW of EC 10 and 15 dS m-1 and canal water (CW) of EC 0.3 dS m-1]. The soil samples were amended with different quality organic materials (BC, FYM, or RS) and soil respiration was recorded at regular intervals. The incubated soil was destructively harvested on days 1, 15, 45, 90, 180, and 365 for analysis of soil parameters like microbial biomass C, water-extractable organic C, soil organic C, pH, and EC. Over 52 weeks of incubation, compared with non-saline soil, cumulative respiration (CR) was reduced by 39–57% with increasing soil salinity. However, individual application of BC, RS, and FYM or their co-application exhibited a beneficial effect on CR at all the soil salinity levels. Among different organic materials, RS amended soil showed maximum carbon (C) loss per g of C added whereas, it was minimum in BC treatment. On the other hand, when BC was co-applied with RS (BC+RS) or FYM (BC+FYM), loss of C per g of C added from the amended soil were increased by 9–16% and 6–13% (from 3‐7% in sole BC amended soil) respectively, even though the input of C in BC+RS and BC+FYM were 88% and 56% more than the individual BC amended soil. The study showed that both pyrolysed and un-pyrolysed organic materials can override the negative effects of salinity on soil microbial activity when applied individually or in combination. In addition, co-application of BC with un-pyrolysed organic materials (FYM or RS) will be more beneficial for soil C stabilization than their individual application.