Eggplant growth in wheat straw-, wheat straw biochar- and compost-amended soils: a field study of CO2 emission dynamics, soil physicochemical, microbial, and nutrient effects

The growth of eggplant (Pusa Safed Baingan-1) was studied during the semi-arid (March to June) and humid sub-tropical (July to September) seasons of New Delhi, India. The individual effects of wheat straw biomass (WSBM), wheat straw biochar (WSBC) and compost versus the combined effect of WSBM plus compost and WSBC plus compost were determined under field conditions. The amendments were made at two different application rates: 1 wt% and 2 wt%. WSBC was successfully prepared in a proprietary kachcha reactor (Indian patent no. 380921), designed using locally sourced clay. Amendments were characterized using elemental analyzer, scanning electron microscopy (SEM), transmission electron (TEM) microscopy, Fourier transform infrared (FTIR) spectroscopy and X-Ray diffraction (XRD). The field study was conducted in 11 (1x1-meter) plots with two replicates. Basic soil health parameters including pH, electrical conductivity (EC), water holding capacity (WHC), bulk density (BD), cation exchange capacity (CEC), soil total nitrogen (STN), soil available nitrogen (SAN), soil organic carbon (SOC), soil available phosphorus (SAP), microbial biomass carbon (MBC) and mineral contents are analyzed. Observable plant growth characteristics (germination percentage, height, number of leaves, fruits, and plant biomass) were also recorded. Biochar amendment was most beneficial for enhancing the majority of these parameters. With respect to the control, a 20% decrease in bulk density, a 30% increase in water holding capacity, a 122% increase in organic carbon, a 175% increase in total nitrogen, a 23% increase in available nitrogen, and a 473% increase in available phosphorus were recorded. Furthermore, with respect to the control, a 115% increase in CEC was recorded using the compost amendment vs 84% with WSBC. Synergism between biochar and compost was reflected by high germination percentage (44%), number of fruits (600%), plant biomass weight (243%) and soil microbial biomass carbon (286%). Biomass amendment failed to show any positive influence. In summary, biochar emerges as a superior choice compared to both biomass and compost when it comes to soil amendments.