Effect of biogas digested slurry based-biochar and digested liquid on N2O,CO2 flux and crop yield for three continuous cropping cycles of komatsuna (Brassica rapa var. perviridis)

Biogas production generates digested slurry, as a byproduct, which can be used as fertilizer after its conversion into digested liquid and biochar. A microcosm-based study was conducted to evaluate the effects of chemical fertilizer (CF), digested liquid (DL) and varying concentrations of biogas digested slurry based-biochar along with DL on N₂O flux, CO₂ flux, soil chemical properties and crop yield for three continuous cropping cycles of komatsuna (Brassica rapa var. perviridis) from April to July 2013. Analyses revealed that DL-treated soils released almost equal cumulative amounts of N₂O and CO₂ as soils treated with CF. The soil mineral-N contents were also similar for the DL- and CF-treated soils while DL application increased the soluble organic carbon (SOC) content of the soil compared to CF treatment. The application of slurry-based biochar increased N₂O and CO₂ flux, which, in turn, appeared to depend upon biochar concentration. The application of biochar probably increased the nitrification rate as biochar-treated soils had higher values of NO₃ ^?-N and lower values of NH₄ ⁺-N compared to soils not treated with biochar at most of the observations. The SOC content was also the highest in biochar-treated soils. The overall crop yield for three cropping cycles was the highest in DL and biochar at low application rate (BL), and it was lower in CF, biochar at medium (BM) and high (BH) application rate. This study indicates that the application of DL could be an effective strategy to minimize the use of CF, without affecting N₂O flux, CO₂ flux, soil mineral N, and increasing crop productivity. The effects of slurry-based biochar on greenhouse gases flux and crop yield depends on the application rate of biochar.