Assessment of crop residue and palm shell biochar incorporation on greenhouse gas emissions during the fallow and crop growing seasons of broccoli (Brassica oleracea var. italica)

Abstract

The impact of broccoli crop residues on greenhouse gas (GHG) emissions may vary with post-harvest management. The incorporation of biochar together with broccoli residues could have a GHG mitigation potential in soil. A field experiment was conducted to evaluate the combined effect of broccoli crop residues and palm shell biochar (PSB) incorporation on GHG emissions during the fallow (post-harvest) and crop growing seasons of broccoli. We also evaluated the plant biomass, N uptake, and soil chemical properties after harvest. The treatments included; No-residues (NR), Residues (R), Residues + 10 t ha−1 PSB (R10), Residues + 20 t ha−1 PSB (R20) and Residues + 40 t ha−1 PSB (R40), arranged in a completely randomized block design. The fallow season had significantly higher GHG emissions than the crop growing season. Incorporation of crop residues in soil significantly increased N2O and CO2 emissions but did not significantly affect CH4 emissions when compared to those of the NR treatment. PSB amendment did not significantly affect N2O, CO2 and CH4 emissions from crop residues and also the biomass and N uptake of the crop residues remaining after broccoli harvest. The application of PSB at 40 t ha−1 significantly increased the total N, total C, C/N ratio and exchangeable K but did not significantly affect soil pH, EC, available P, exchangeable Ca and Mg, and CEC. The large amounts of N2O and CO2 emissions emitted from broccoli crop residues during the fallow season may necessitate higher biochar application rates to achieve the GHG mitigation potential of biochar while maintaining a high soil nutrient status. The combined incorporation of broccoli crop residues with biochar requires further evaluation in terms of GHG emissions, soil nutrient status and broccoli crop yield in different soil types and tillage systems.