Sewage Sludge Application Effects on Phosphorus Uptake by Cucumber and on Rhizosphere and Non-rhizosphere Soils Under Greenhouse Conditions

Within the growing greenhouse cultivation that we are facing these years, the use of phosphorus (P) fertilizers will inevitably increase. In this study, we used five different sewage sludges (SSs) as a P fertilizer, and studied the effect of these SSs on P uptake by cucumber plant (Cucumis sativus var. Negin L.), and specified their effects on availability and speciation of P in the rhizosphere and non-rhizosphere soils. A sandy clay loam texture soil was used and treated with 100 mg P kg−1 of five different SSs. Cucumber plants were grown under greenhouse conditions and after nearly 2 months, the plants were harvested. The plant’s parts, root, shoot, and fruit were separated. Rhizosphere and non-rhizosphere soils for each treatment were also separated. The addition of different SSs increased shoot dry weight and also increased P content in root and shoot compared to control soil. The results showed that rhizosphere soil had a lower content of P extracted by water or Olsen compared to the non-rhizosphere soil. The mean proportion of HPO4−2 in the SS-treated soils in the rhizosphere soil (74.3%) was significantly higher than non-rhizosphere soil (66.3%), while the proportion of H2PO4− in non-rhizosphere soil (29.8%) was significantly higher than rhizosphere soil (21.2%). Generally, the HPO4−2 and H2PO4− were the dominant species of P in all treatments. The water-extractable P was better correlated to P content in shoot compared to Olsen-extractable P. This research offers additional insights into the effects of SS on soil solution characteristics and the availability of P in rhizosphere and non-rhizosphere soils which will be useful in understanding P uptake from soils treated with SS.