Cadmium (Cd) is naturally present in earth crust as a trace element, while its concentration varies because of its solubility and mobility1–4. Human beings and animals are greatly exposed to heavy metals because of the contaminated food chain 5. Cd is recognized as a serious global concern and its concentration in industrial and sewage wastewater, and drinking water exceeds the permissible limits (0.003 mg L− 1) 1. Wastewater irrigation to the farmlands has become a serious environmental threats because of food chain deterioration 6. Cd is highly reactive and mobile, which has the potential to influence the plants growth.
The increase of heavy metal accumulation in cultivated soils leads in deteriorating the soil health and enhancing the plant Cd uptake, which affects food safety and quality 7,8. Nowadays, various soil restoration strategies (physical, chemical and biological) are adopted in order to improve soil health and minimize food security risks 9. Additionally, the use of organic materials as a soil amendment could use as a practical and cost effective strategy to restore polluted soils through changing the heavy metals mobility and bioavailability 10,11. However, several research studies have shown that organic based soil amendments (compost, biofertilizers, biochar and manure) are more effective to ameliorate the soil health and minimize the use of chemical fertilizer due to their less production cost 8,12−15.
Moringa (Moringa oleifera L.) that is also known as miraculous tree (evergreen), which is widely grown in tropical areas of Pakistan, having enough tolerance to drought and is easily available at low cost. Its tree contains most important constituents including proteins, carbohydrates, fatty acids, vitamins, flavonoids and phenolic acids. It has a number of applications in the medical field, for example, anti-inflammatory, antihypertensive activity and analgesic, weight losses, etc. It has attained much attention by the researchers because of its environmental friendly usage. To some extent, it acts as plants growth activator and reduces drought and heavy metals stress on plants 16. Previous study proposed by 17 studied that Moringa seeds were used for wastewater treatment and effectively removed Cd, Cu, Cr and Pb from drinking water. Similarly, its seed ash was also used in the study conducted by 18 for the removal of fluoride from aqueous solutions. Moringa seeds acts as a natural organic biosorbent for the stabilization of heavy metals 19. It can be demonstrated that addition of moringa husks, pods, and seeds showed the noticeable removal of Pb(II) from contaminated water 20.
Compost is organic carbon and nutrient rich organic material that can be used as a soil amendment to substitute the chemical fertilizers in agricultural production. The incorporation of compost prominently improves the physical structure and fertility status, microbial communities in degraded soils, improves crop biomass and promote crop growth 12,21. In a similar manner, it has the ability to act as biosorbent for the sorption of heavy metals from polluted soils and water3. It has been demonstrated that the compost is a suitable candidate to minimize the risk of crop growth, yield and economic losses through ameliorating the soil properties and thereby, ensure the human health 11,22. Abbas et al. 12 found that incorporation of compost effectively reduced the toxic elements from polluted water by 85–89% through chemical absorption.
Press mud is the by-product of sugarcane obtained from the sugar industry after the clarification process of sugarcane juice. Press mud is a dark brown, spongy and amorphous material containing sugar, fiber and coagulated colloids including soil particles, and mainly comprises of CaO, organic matter, nitrogen, phosphorus, potassium, calcium, sulphur in varying amounts 21. 16 demonstrated that addition of soil amendments such as press mud, poultry manure farmyard manure (FYM) and fish manure to Cr polluted soil. Results revealed that these amendments have potential to stabilize Cr in soil. It can be demonstrated that press mud had been recognized as the filter cake which can contribute to enhance the soil fertility status and can create extra binding sites for the toxic metals adsorption and complexation 23. Press mud has the ability to buffer the soil pH and reduces the uptake of heavy metals. It contains functional groups like hydroxyl ions that play an important role in the adsorption of heavy metals 24,25, and is also considered a key source of NPK and carbon contents. Press mud is considered a key source of NPK and carbon contents 23. Sabir el al. 26 confirmed that press mud incorporation as a soil amendment could help to improve soil health, structure and thereby, reduces the metals accumulation in plant tissues.
Maize (Zea mays L.) belongs to Gramineae family and is recognized as one of the most important nutritious cereal crop that is also consumed by animals as a forage 10. It is widely grown all around the globe and has greater potential to uptake heavy metals. Particularly, this crop being the highest yielding cereal crop in the world has a significant importance in Pakistan. There is only little scientific knowledge is present about the effect of ME as a biofertilizer, compost and press mud on the growth, metabolic and antioxidant enzymes of plants. Thus, the comparative efficiency of compost, press mud and M. oleifera leaf extract was assessed for wastewater irrigated soil restoration as well as reducing the Cd stress on maize plant in calcareous soil condition. The prime objectives of the current study were to evaluate the effect of compost, press mud and M. oleifera leaf extract on Cd solubility and maize growth in polluted soil. Additionally, to examine the efficacy of these soil amendments on soil and plant nutrients status.