Water Research and Technology Center, Univ. of Carthage, P.O. Box 273, Soliman, 8020, Tunisia.
Center for Sustainable Development, College of Arts and Sciences, Qatar Univ., P.O. Box 2713, Doha, Qatar.
J Environ Qual. 2020 Jul;49(4):973-986. doi: 10.1002/jeq2.20093. Epub 2020 Jun 10.
Urban sewage sludge (USS) is increasingly applied to agricultural soils, but mixed results have been reported because of variations in reuse conditions. Most field trials have been conducted in cropping systems, which conceal intrinsic soil responses to sludge amendments due to the rhizosphere effect and farming practices. Therefore, the current field study highlights long-term changes in bare soil properties in strict relationship with soil texture and USS dose. Two agricultural soils (loamy sand [LS] and sandy [S]) were amended annually with increasing sludge rates up to 120 t ha yr for 5 yr under unvegetated conditions. Outcomes showed a USS dose-dependent variation of all studied parameters in topsoil samples. Soil salinization was the most significant risk related to excessive USS doses. Total dissolved salts (TDS) in saturated paste extracts reached the highest concentrations of 37.2 and 43.1 g L in S soil and LS soil, respectively, treated with 120 t USS ha yr . This was also reflected by electrical conductivity of the saturated paste extract (EC ) exceeding 4,000 µS cm in both treatments. As observed for TDS, fertility indicators and bioavailable metals varied with soil texture due to the greater retention capacity of LS soil owing to higher fine fraction content. Soil phytotoxicity was estimated by the seed germination index (GI) calculated for lettuce, alfalfa, oat, and durum wheat. The GI was species dependent, indicating different degrees of sensitivity or tolerance to increasing USS rates. Lettuce germination was significantly affected by changes in soil conditions showing negative correlations with EC and soluble metals. In contrast, treatment with USS enhanced the GI of wheat, reflecting higher salinity tolerance and a positive effect of sludge on abiotic conditions that control germination in soil. Therefore, the choice of adapted plant species is the key factor for successful cropping trials in sludge-amended soils.
城市污水污泥（USS）越来越多地应用于农业土壤，但由于再利用条件的变化，报道的结果喜忧参半。大多数田间试验都是在作物系统中进行的，由于根际效应和耕作实践，这些试验掩盖了土壤对污泥改良剂的固有反应。因此，目前的野外研究强调了裸露土壤性质的长期变化，这与土壤质地和 USS 剂量密切相关。在无植被条件下，两种农业土壤（壤土砂[LS]和砂[S]）每年用递增的污泥量进行施肥，污泥量最高达 120 t ha yr ，共持续 5 年。结果表明，在表土样品中，所有研究参数都随 USS 剂量呈剂量依赖性变化。土壤盐渍化是与过量 USS 剂量相关的最显著风险。饱和糊提取物中的总溶解盐（TDS）在 LS 土壤和 S 土壤中分别达到 37.2 和 43.1 g L 的最高浓度，分别用 120 t USS ha yr 处理。在这两种处理中，饱和糊提取物的电导率（EC）也超过 4,000 µS cm ，反映了这一点。与 TDS 一样，由于 LS 土壤的细粒含量较高，肥力指标和生物可利用金属也因土壤质地而异。通过计算生菜、紫花苜蓿、燕麦和硬质小麦的发芽指数（GI）来估计土壤的植物毒性。GI 因物种而异，表明对增加的 USS 速率有不同程度的敏感性或耐受性。生菜的发芽受到土壤条件变化的显著影响，与 EC 和可溶性金属呈负相关。相比之下，用 USS 处理提高了小麦的 GI，这反映出更高的耐盐性和污泥对控制土壤中发芽的非生物条件的积极影响。因此，选择适应性强的植物物种是成功进行污泥改良土壤作物试验的关键因素。
