Contents lists available at ScienceDirect Ecotoxicology and Environmental Safety journal homepage: www.elsevier.com/locate/ecoenv The quantity/intensity relation is affected by chemical and organic P fertilization in calcareous soils Jafar Shahabifar a,b , Ebrahim Panahpour b, ⁎ , Farhad Moshiri c , Ali Gholami b , Mehrzad Mostashari d a PhD student of Soil Science, Khouzestan Science and Research Branch, Islamic Azad University, Khuzestan, Iran b Department of Soil Science, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran c Assistant Professor of Soil and Water Research Institute (AREEO), Karaj, Iran d Associate Professor of Soil and Water Research Section, Qazvin Agricultural and Natural Resources Research and Education Center, Agricultural and Natural Resources Research Center, (AREEO), Qazvin, Iran ARTICLE INFO Keywords: MSWC Isotherm models Manure Phosphorous uptake Surface sorption Wheat (Triticum aestivum L.) ABSTRACT The use of organic fertilization increases the availability of phosphorus (P) in calcareous soils by affecting the colloidal properties of soils. Accordingly, it was hypothesized that chemical and organic fertilizers affect P availability in calcareous soils by influencing P sorption and buffering capacity. The objective was to investigate the quantity/intensity (Q/I) relation in calcareous soils as affected by chemical and organic P fertilization. Three different soil types with different Olsen-P values including Qazvin1 (very low P, VLP), Qazvin2 (low P, LP) and Dizan (medium P, MP) were fertilized with 50 mg P kg -1 soil using triple superphosphate (TSP), sheep manure (SM), and municipal solid waste compost (MSWC). The treated experimental soils were incubated for 90 days, and P sorption and buffering capacity indexes were determined using calcium chloride solutions in a range of 0–100 mg P L -1 . A greenhouse experiment was conducted to determine wheat (Triticum aestivum L.) response to the experimental treatments. Wheat P content at tillering (60 days after planting) was determined. The SM and TSP treatments were the most efficient sources of P for plant use in the greenhouse, as they resulted in the highest wheat growth and P content. The incubation data were fitted to Langmuir, Freundlich, Temkin and surface sorption isotherm models. Langmuir model, as the best fitted one, indicated the highest P sorption (A) was resulted by the SM treatment for VLP and LP soils, compared to the other treatments. According to the model, the SM and MSWC treatments resulted in the least (0.04) and the highest (1.11) sorption energy (K) by the VLP soil, respectively. In the VLP soil the SM and MSWC treatments, and in the LP soil the MSWC treatment decreased P sorption, at the final concentration of P (100 mg L -1 ), compared to the control treatment. Organic fertilizers decreased buffering index, phosphorous buffering capacity, and K1 indexes in the VLP soil, compared to the control treatment. The corresponding reductions for SM were equal to 35.99, 2.7, 1.19 mL P g -1 and for MSWC were equal to 12.33, 36.2 and 1.19 mL P g -1 . In the VLP and MP soils, (compared with control), the SM treatment decreased the rates of maximum buffering capacity at 0.38 and 0.52 mL P g -1 , respectively. There were high and significant correlations among the soil P buffering indexes with soil and wheat P content. Fertilization affected soil P availability by affecting the Q/I relation and the buffering capacity indexes. It is possible to predict plant response to available P using the tested fitting models. 1. Introduction Phosphorus (P) is among the most important nutrients affecting plant growth and yield production. However, due to its little solubility, P can easily precipitate and become unavailable to plants. Inorganic P in chemical fertilizer is more reactive than organic P such as manure P (Barnett, 1994; Whalen and Chang, 2002). However, organic fertiliza- tion is also an important source of nutrients. The extra use of chemical fertilization can result in P loss by surface runoff, which can result in eutrophication, with economical and environmental significance (Hartikainen et al., 2010; Chen and Lin, 2016). It is, accordingly, im- portant to indicate how P availability may also be affected by organic fertilization. Iyamuremye et al. (1996) found the highest concentrations of P in animal manure extracted with calcium chloride. Using soils treated with cow and chicken manures, as well as with chemical fertilizer, https://doi.org/10.1016/j.ecoenv.2019.01.058 Received 18 October 2018; Received in revised form 11 January 2019; Accepted 14 January 2019 ⁎ Corresponding author. E-mail addresses: e.panahpour@iauahvaz.ac.ir, e.panahpour@gmail.com (E. Panahpour). Ecotoxicology and Environmental Safety 172 (2019) 144–151 0147-6513/ © 2019 Elsevier Inc. All rights reserved. T