It is essential for the sustainable development of agriculture to enhance nitrogen use efficiency (NUE) of crop plants by increasing yield and reducing nitrogen (N) losses. Biochar-based fertilizer (BF) has received increasing attention because of its full play to the advantages of chemical compounds with sufficient N and less N loss risk with good adsorption characteristics, but this potential was seldom reported for open-field vegetable crops, NUE of which were significantly lower than cereal crops. A field trial was conducted to investigate the efficacy of BF on NUE in vegetable cropping system by comparison with chemical fertilizer (CF) and partial substitution of organic fertilizers to chemical fertilizers (COF). The yield, plant N uptake, residual soil mineral N, and N losses via leaching and ammonia volatilization from an open vegetable (water spinach, Ipomoea aquatica L.) field were analyzed. The results indicated that BF treatment had significantly higher yield, plant N uptake, and NUE (agronomic efficiency and recovery efficiency as the NUE indicators), compared with those of CF and COF treatments. N losses via leaching were respectively accounted for 53.30%, 37.74%, and 33.39%; and N losses via ammonia volatilization were respectively accounting to 1.13%, 0.78%, and 1.54% of N fertilizer applied (at a rate of 200 kg N/ha) in CF, COF, and BF treatments. Despite the increasing ammonia volatilization due to the alkalinity of biochar, BF treatment significantly enhance NUE by increasing N uptake by water spinach and minimizing N losses via leaching. This study suggested that BF could serve as a promising slow-release N fertilizer for sustainable N management in field vegetable production and provided critical information for the development and dissemination of BF management guidelines.

This study aimed to evaluate the health risks of cadmium (Cd), lead (Pb), inorganic arsenic (As), and nitrate exposure through the consumption of bivalves and vegetables collected from local markets in Ho Chi Minh City. The present study analyzed four favorite bivalve species (Meretrix lyrate; Perna viridis; Anadara subcrenata; Anadara granosa) for concentrations of Cd, Pb, and inorganic As and 9 vegetable species (Brassica juncea; Brassica integrifolia; Brassica rapa chinensis; Nasturtium officinale; Lactuca sativa; Ipomoea aquatica; Amaranthus gangeticus; Ipomoea batatas; Spinacia oleracea) for concentrations of Pb and nitrate. The target hazard quotient (THQ) and target cancer risk (TR) were calculated to estimate non-carcinogenic and carcinogenic health risks, respectively. For bivalves, Cd and inorganic As were present at relatively lower concentrations, whereas a relatively higher accumulation of Pb was recorded. The THQ for Cd, Pb, or inorganic As was below the threshold of 1, suggesting no potential health risks. In the case of vegetables, Pb was present at relatively low concentrations, while nitrate accumulation was at relatively high concentrations. The THQ for nitrate was higher than the threshold of 1, suggesting a potential health risk. The combined effects are estimated according to the hazard index (HI), which shows the health risks associated with the consumption of these bivalves and vegetable species. Therefore, continuous and excess consumption for a lifetime of more than 70 years has a probability of target cancer risk.