title: Optimizing available phosphorus in calcareous soils fertilized with diammonium phosphate and phosphoric acid using Freundlich adsorption isotherm.
abstract: In calcareous soils, phosphorus (P) retention and immobilization take place due to precipitation and adsorption. Since soil pH is considered a major soil variable affecting the P sorption, an acidic P fertilizer could result in low P adsorption compared to alkaline one. Therefore, P adsorption from DAP and phosphoric acid (PA) required to produce desired soil solution P concentration was estimated using Freundlich sorption isotherms. Two soils from Faisalabad and T. T. Singh districts were spiked with 0, 10, and 20 % CaCO3 for 15 days. Freundlich adsorption isotherms (P = aC(b/a)) were constructed, and theoretical doses of PA and DAP to develop a desired soil solution P level (i.e., 0.20 mg L(-1)) were calculated. It was observed that P adsorption in soil increased with CaCO3. Moreover, at all the levels of CaCO3, P adsorption from PA was lower compared to that from DAP in both the soils. Consequently, lesser quantity of PA was required to produce desired solution P, 0.2 mg L(-1), compared to DAP. However, extrapolating the developed relationship between soil CaCO3 contents and quantity of fertilizer to other similar textured soils needs confirmation.
authors.affiliation: Soil Science and Plant Nutrition, School of Earth and Environment, University of Western Australia, Crawley, WA 6009, Australia ; Nuclear Institute for Agriculture and Biology, P.O. Box 128, Jhang Road, Faisalabad 38000, Pakistan.
authors.forename: Asif
authors.initials: A
authors.lastname: Naeem
authors.forename: Muhammad
authors.initials: M
authors.lastname: Akhtar
authors.forename: Waqar
authors.initials: W
authors.lastname: Ahmad
mesh_terms: D000327:Adsorption; D002119:Calcium Carbonate / Q000737:chemistry*; D003198:Computer Simulation; D005308:Fertilizers; D005620:Freund's Adjuvant / Q000737:chemistry*; D008422:Materials Testing; D008956:Models, Chemical; D010710:Phosphates / Q000737:chemistry*; D010758:Phosphorus / Q000737:chemistry*; D012987:Soil / Q000737:chemistry*
chemical_list: D005308:Fertilizers; D010710:Phosphates; D012987:Soil; C024788:ammonium phosphate; D010758:Phosphorus; D005620:Freund's Adjuvant; D002119:Calcium Carbonate