Treated Livestock Wastewater Irrigation Is Safe for Maize (Zea mays) and Soybean (Glycine max) Intercropping System Considering Heavy Metals Migration in Soil–Plant System

Abstract

Water deficit is a major problem affecting crop production worldwide. The use of treated wastewater in irrigation systems improves soil health and enhances crop growth and productivity. However, it has been characterized as a source of heavy metals. The unknown is how heavy metals’ movements would be impacted under an intercropping system when irrigated with treated wastewater. Understanding the dynamic of heavy metals in soil–plant systems is essential for environmental risk assessment and sustainable agriculture. A greenhouse pot experiment was conducted to explore the effects of treated wastewater irrigation on plant growth, soil chemical properties, and the movements of Zn, Cu, Pb, and Cd from soil to plants in monoculture and intercropping systems. Maize and soybean were selected as the test crops and groundwater and treated livestock wastewater as the water sources. This study found that treated wastewater irrigation and intercropping systems synergically increased the soil nutrient content and crop growth. The concentrations of Zn, Pb, and Cd were significantly higher in leaves compared to other plant parts contrastingly to Cu, which was higher in roots. In addition, treated wastewater irrigation increased grain nutrient content in mono- and intercropping systems while the concentration of heavy metals was in the acceptable range for human consumption. The enrichment degree of Cu and Pb due to treated livestock wastewater irrigation relative to groundwater irrigation was higher in uncultivated soil compared with cultivated soil. This study showed that the intercropping system facilitated heavy metals’ transfer from soil to plant except for Cd. These findings provide guidelines for a safe utilization of treated wastewater in agricultural systems and to reduce freshwater use pressure.

Hyperaccumulator Solanum nigrum L. Intercropping Reduced Rice Cadmium Uptake under a High-Bed and Low-Ditch Planting System

“…This situation might be explained by the potential accumulation of Cd in water under flood cultivation and the lack of significant contact between rice plants and the contaminated soil under the high-bed and low-ditch cultivation mode. This study is in line with previous studies suggesting that intercropping increases HM TF [1,5,32]. This study aligns with previous studies suggesting that the use of hyperaccumulators such as Solanum nigrum L. reduces HM concentration in soil [13,15].…”

“…A significant decrease in rice Cd uptake was also observed in flood cultivation mode, which might be due to the significant amount of Cd that can be accumulated in water. This study supports previous studies suggesting that the intercropping system decreases plant HM uptake [1,5,11]. In addition, it is important to mention that less Cd was accumulated in rice grown under the high-bed and low-ditch cultivation mode [28].…”

“…The intercropping system is a farming practice that enables crops to share the available resources and complement each other [1]. It can also affect heavy metal uptake by plants due to the alteration of the rhizosphere microorganism community and root exudation [7].…”

“…The absence of healthy soil would severely curtail our ability to produce food, which would increase the challenges in feeding the world's population. Heavy metal (HM) contamination of soil is a prominent environmental problem that humanity is currently facing and has attracted much attention from both industry and the general public [1][2][3][4]. Soil HM contamination is mainly due to the diffusion, deposition, and accumulation of HMs in industrial solid waste as well as agricultural land irrigated with wastewater containing HMs [2,3,5].…”

“…In comparison to monocropping, the intercropping system is conducive to field ventilation and light penetration, prevention, and pest and disease control while increasing the accumulation of organic matter and improving yields [1,5,7,12]. Intercropping is a well-established agricultural practice that substantially contributes to the sustainable development of agriculture [18,19].…”