| Water scarcity and water pollution are two major problems that almost every country in the world is facing.Global water scarcity is expected to reach 40%by 2030,threatening food security,as agriculture accounts for about 69%of global water use.In addition,the demand for food is increasing due to continuous population growth.Therefore,improving agricultural water use efficiency and finding alternative irrigation water resources is the only way to alleviate these challenges.The world’s wastewater volume is about 380 km~3 annually,equivalent to 15%of agricultural water use.With the advancement of urbanization,the amount of wastewater will continue to increase.Thus,treated wastewater could be an alternative water source for irrigation.Wastewater contains nutrients such as nitrogen and phosphorus,improving soil health and plant growth.However,it is also considered as source of pollutants such as heavy metals,not all of which can be removed in wastewater treatment plants,threatening soil health of farmland irrigated with treated wastewater.Although the use of treated wastewater for farmland irrigation has been around for decades,its safety is still inconclusive.Intercropping system is a commonly used cultivation method that improves resource use efficiency and helps restore the ecological and environmental benefits of cultivated soil.However,the effect of treated wastewater irrigation on heavy metal migration under intercropping systems remains unclear.In addition,straw return is also one of the widely used straw treatment methods,but under intercropping conditions,straw return and plant-soil feedback(plant growth process accompanied by root release secretions and microbial community composition changes that affect the changes of biotic and abiotic processes in the soil,these changes affect the growth of the next crop in the soil)(PSF)effects on crop growth and soil heavy metal migration are still relatively lacking.Therefore,understanding the migration patterns of heavy metals in soil-plant systems under intercropping patterns in livestock wastewater irrigation is essential for assessing heavy metal risks and the sustainable development of agriculture.This study aims to:1)determine the effects of treated livestock wastewater irrigation on soil chemical properties and plant growth under mono and intercropping system;2)determine the effects of the intercropping system on Zn,Cu,Pb,and Cd migration in the soil–plant system in wastewater irrigation;3)determined the effects of PSF combined with straw incorporation on soil chemical properties and heavy accumulation and migration in soil-plant system in wastewater irrigated-soil under mono and intercropping system;4)explore whether PSF and straw application increase plant growth and yield under different planting patterns in wastewater irrigated soil;5)determine the impact of root exudates and treated wastewater irrigation on crop growth,heavy metals migration in soil-plant system and soil bacterial composition under maize/soybean intercropping system.The followings are how this work has been carried out and the summary of the obtained results:1.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.It was 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,the concentration of heavy metals in grains was in the acceptable range for human consumption.Cu and Pb enrichment factor due to treated livestock wastewater irrigation relative to groundwater irrigation was higher in uncultivated soil than in cultivated-soil.This study showed that the intercropping system facilitated heavy metals’transfer from soil to plant except for Cd.2.A two-phase experiment integrating PSF and straw incorporation was conducted using monocropped and intercropped maize/soybean irrigated with groundwater and treated wastewater to determine the effects of PSF combined with straw incorporation on soil chemical properties,explore whether PSF and straw application increase crop yield;and to elucidate the impacts of soil PSF and straw incorporation on heavy metals migration in soil-plant system.The results showed 0.73 in groundwater and 0.79 in wastewater irrigation of maize relative yield total(RYTM)in the conditioning phase.In contrast,an overyielding was observed in the feedback phase combined with straw incorporation with1.10 and 1.20,respectively,in groundwater and wastewater irrigation.An overyielding was observed for soybean during the feedback phase in all treatments,with 1.09,1.10,and 1.06 of soybean relative yield total(RYTS)in groundwater irrigation and 1.36,1.14,and 1.18 in wastewater irrigation.In addition,it was found that PSF combined with straw incorporation increases heavy metals TF with more pronounced effects under intercropping system.No potential health risk was recorded considering heavy metals movement in soil-plant system with its content in soil and grains under permissible limits.3.Another greenhouse experiment assessed the impacts of root exudates on plant growth,heavy metals migration in soil-plant system,and soil bacterial community composition under intercropped maize/soybean.Maize and soybean used in the previous experiment were used as test crops grown in mono and intercropping system and irrigated with groundwater and treated wastewater with three levels of root exudates treatments.The results showed that root exudates application increases plant growth and soil nutrient content.Root exudates application decreases heavy metals migration in soil-plant system with a greater impact under intercropping system.Furthermore,soil bacterial composition was increased with root exudates in groundwater and wastewater-irrigated soil.This study strongly suggests that root exudates could be used as an alternative to increase plant growth and soil health while maintaining toxic heavy metals concentration in soil and plant irrigated with wastewater under permissible limits. |
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