Greywater irrigation and Moringa-derived biochar in contrasting dryland soil materials: salinity, sodicity and water-retention trade-offs

Abstract Background Greywater reuse can reduce pressure on freshwater resources in dryland areas, but its suitability depends on the combined behavior of irrigation-water chemistry, amendment properties and the receiving soil material. This study examined the short-term response of three contrasting Sudanese dryland soil materials to untreated washbasin and ablution greywater with and without Moringa-derived biochar in a 45-day soil-column experiment. Results The greywater was slightly alkaline and low in salinity, with pH 7.44–7.98 and EC 0.436–0.750 dS m⁻¹, while SAR ranged from 8.45 to 16.40. The biochar aqueous extract was alkaline and sodium-rich, with pH 9.24, EC 1.706 dS m⁻¹, soluble Na⁺ of 25.00 meq L⁻¹ and SAR of 64.55. Biochar increased residual gravimetric moisture in the amended upper layer by 16.7% in Vertisol, 22.1% in Entisol and 59.3% in Aridisol. Mean SAR was higher in the amended Vertisol and Aridisol, although these contrasts were not statistically significant. Conclusions Moringa-derived biochar improved short-term moisture retention under the tested greywater irrigation regime, but its sodium-rich chemistry introduced a soil-dependent sodicity concern. Greywater–biochar reuse should therefore be considered only after joint assessment of greywater chemistry, biochar-extract chemistry and the baseline properties of the receiving soil material.