Biochar for Wastewater Treatment and Soil Improvement in Irrigated Urban Agriculture: Single and Combined Effects on Crop Yields and Soil Fertility

Abstract

This work evaluated the agronomic and soil fertility effects of using municipal wastewater or anaerobically treated wastewater for irrigation and applying biochar to a soil from the Guinea savanna agroecological zone of Ghana. For this purpose, untreated municipal wastewater (WW), the effluent of an anaerobic wastewater filtration system (TWW), and clean water (CW) were used as irrigation water in a pot trial. Additionally, rice-husk biochar in the form of raw biochar (RB), water-washed biochar (WB), and biochar used as wastewater filter material (FB) were added to the soil, testing the influence on soil fertility and crop yield. Lettuce and carrot were selected for the pot study, grown on soil mixed with the biochar types at 20 t ha −1 and irrigated with either WW, TWW, or CW. Our results indicated higher crop growth morphology and yields (up to 90% increase) by WW and TWW than CW. The average yield of carrot (34.1 g pot −1 ) and lettuce (29.3 g pot −1 ) with TWW irrigation were the highest, followed by 31.2 and 27 g pot −1 with WW, then the lowest yields of 21.7 and 19.5 g pot −1 of carrot and lettuce irrigated with CW respectively. Compared to WW, TWW was more beneficial to plant development, causing an up to 10% increase in crop yields. Soils with FB and WB produced similar agronomic effects and plant nutrient concentrations but were lower than pots amended with RB. Nevertheless, combining RB with TWW showed increasing effects on pH, CEC, and P availability in the highly weathered acidic soil. The results suggest a beneficial effect of biochar-filtered wastewater on soil fertility and crop growth, offering the potential to enhance resource use efficiency in irrigated urban agroecosystems.

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