Biochar Is Superior to Organic Substitution for Vegetable Production—A Revised Approach for Net Ecosystem Economic Benefit

Biochar amendment and substituting chemical fertilizers with organic manure (organic substitution) have been widely reported to improve intensive vegetable production. However, considering its high potential for reducing carbon and reactive nitrogen (Nr) footprints, very few comprehensive evaluations have been performed on the environmental and economic aspects of biochar amendment or organic substitution. In this study, the comprehensive environmental damage costs from carbon and Nr footprints, measured using the life cycle assessment (LCA) methodology, followed a cradle-to-gate approach, and the carbon storage benefits were incorporated into the newly constructed net ecosystem economic benefit (NEEB) assessment frame in addition to the conventional product income–input cost-benefit methods. One kilogram of harvested vegetables for carbon/Nr footprints and one hectare of cultivated land per crop for cost and benefit were adopted as functional units considering the multi-cropping characteristics for intensive vegetable production. Five fertilization treatments were included: no fertilizer (CK); synthetic fertilizer application (SN); biochar amendment (NB); organic substitution (NM); and a combination of biochar and organic substitution (NMB). These were investigated for five consecutive years of vegetable crop rotations in a typically intensified vegetable production region in China. Adopting the revised NEEB methodology, NB significantly reduced carbon footprint by 73.0% compared to no biochar addition treatment. Meanwhile, NB significantly increased the total benefits by 9.7% and reduced the environmental damages by 52.7% compared to NM, generating the highest NEEB, making it the most effective fertilization strategy among all treatments. It was 4.3% higher compared to NM, which was not significant, but significantly higher than SN and NMB, by 23.0% and 13.6%, respectively. This finding highlights the importance of considering carbon storage benefit for properly assessing NEEB, which is important for developing effective agricultural management strategies and promoting intensive vegetable production with a more sustainable approach.