Impact of sewage sludge, nanoparticles, and clay minerals addition on cucumber growth, phosphorus uptake, soil phosphorus status, and potential risk of phosphorus loss

There is little information about the impact of sewage sludge, nanoparticles, and clay minerals on cucumber (Cucumis sativus L.) growth and phosphorus content in different plant parts. In this study we treated a soil with different rates of sewage sludge (1%, 5%, and 10%), along with two nanoparticles (SiO₂ and nano-montmorillonite at 0 and 1%), and two clay minerals (zeolite and vermiculite at 0 and 3%). We aimed at investigating the impact of these amendments on cucumber growth, phosphorus content in root, shoot, and fruit, phosphorus content in rhizosphere and non-rhizosphere soils, and determining the impact of these amendments on the potential risk of phosphorus loss from soil. Plant growth in the soil treated with sewage sludge at 1% and 5% was higher than that at 10% sewage sludge, while the cucumber in the 10% sewage sludge plus 1% nano-montmorillonite-treated soil dried out. Phosphorus content in fruit was higher than in root and phosphorus in root was higher than that in shoot. Cucumber plant in the 10% sewage sludge treated soil had the highest amount of phosphorus compared to the other treatments, while plants in the nanoparticles and clay minerals treatments had lower content of phosphorus than the control. The highest phosphorus content was extracted from soil treated with 10% sewage sludge, while the lowest was extracted from the soil treated with nanoparticles and clay minerals. In average of all treatments, soil phosphorus extracted by water-extractable phosphorus in the rhizosphere soil was higher than phosphorus in the non-rhizosphere soil. The results indicated that calcium chloride-extractable phosphorus was more effective in predicting phosphorus uptake than water-extractable phosphorus and Olsen-extractable phosphorus. Also, the soil treated with sewage sludge at 5% and 10% would potentially increase the risk of phosphorus losses. We concluded that the soil treated with 1% sewage sludge, with or without nanoparticles or clay minerals, could provide the amount of phosphorus required for the growth of cucumber, while there was no obvious potential risk of phosphorus loss, making this treatment more beneficial for cucumber.