Evaluation of the Interaction of Biochar, Pumice, and Arbuscular Mycorrhiza Fungi in Wastewater Irrigation in Terms of Soil and Pepper Plant Productivity and Heavy Metal Contamination

Biochar (B) and pumice (P) enhance water retention and soil-plant productivity, while arbuscular mycorrhizal fungi (AMF) improve plant access to soil moisture and promote productivity. The use of recycled wastewater (WW), is an effective approach to protect freshwater resources, increases soil-plant fertility, reduces the need for fertilizer, and contributes to the sustainable European Green Consensus by reducing the discharge of WW. However, the heavy metal (HM) content of WW can negatively affect the environment, soil, and plant health. The study investigated the B, P, and their combination (B+P) in the soil of pepper irrigated with different water qualities in conditions with and without AMF, hypothesized that B+P under AMF would limit HM contamination in irrigation with WW, in addition to reducing irrigation water quantity (IWQ) and increasing irrigation water productivity (IWP), and soil-plant efficiency. As a result, IWP increased between 14% and 38% in parallel with the IWQ reduction by 2% to 15%, and yield increased between 7% and 20% with B+P, B, P, respectively, also AMF and WW. These treatments increased the yield of the plant by improving the organic matter, total nitrogen, and cation exchange capacity of the soil, but a moderate increase in soil salinity for B and WW treatments, thus increasing the electrolyte leakage. Although there was more Fe, Cu, Mn, Zn, Pb in the soil of the B, P, B+P and AMF and WW, no-contamination was observed and B, P, B+P increased the plant's uptake of Fe, Cu, Mn, Zn, Pb while limiting the uptake of Cd, Cr, Ni, and AMF also created a barrier in the uptake of HM. However, in WW, the accumulation of HM in pepper was higher but did not exceed threshold values. It was found that B+P under AMF conditions can be safely used in irrigation with WW due to its effects in reducing HM, its regulating properties of soil and plants, and its increase in IWP.