Nutrient supplementation increased growth and nitrate concentration of lettuce cultivated hydroponically with biogas slurry

Abstract

Abstract Recycling of biogas slurry via vegetable production is a multi-benefit and sustainable utilization strategy regarding agriculture and environment. A glasshouse experiment was conducted to investigate the effects of phosphorus (P) and iron (Fe) supplementation on growth and quality of lettuce cultivated hydroponically with diluted biogas slurry. The results showed that direct supplementation of P into diluted biogas slurry together with Fe improved the lettuce growth significantly, and decreased the root to shoot ratio. However, growth responses of lettuce to single addition of P or Fe into diluted biogas slurry were not significant. In addition, supplementation of P and Fe improved leaf chlorophyll content (determined as SPAD value), nitrate concentration significantly or slightly of the lettuces but not vitamin C content. However, addition of P and Fe or microelements through foliar spray is not effective in enhancement of growth and quality except for improving leaf SPAD. In conclusion, as a nutrient solution, the tested biogas slurry needs Fe and P supplementation, and P should be added together with Fe or post Fe supplementation in terms of lettuce yield. Also, direct addition of Fe into diluted biogas slurry was better than foliar spray.