Phosphorus Sorption and Desorption in Soils Amended with Subabul Biochar
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FULL-LENGTH RESEARCH ARTICLE
Phosphorus Sorption and Desorption in Soils Amended with Subabul Biochar I. Rashmi1,2 • Pramod Jha2 • A. K. Biswas2
Received: 12 June 2019 / Accepted: 9 October 2019 Ó NAAS (National Academy of Agricultural Sciences) 2019
Abstract Phosphorus sorption mechanism after biochar application is important to understand the bioavailability of P to crops. The knowledge on P adsorption mechanism on biochar is still poorly understood, and therefore the present study was undertaken with varying biochar rates (0, 1, 3, 5%) on two soils, i.e., one taken from control plot (S1) and another from 100% NPK (S2) plots under long-term fertilizer experiment of red soils by fitting the equilibrium solution and sorbed concentrations of P using adsorption isotherms. Results showed that P sorption increased with higher biochar application rates and soils of S2 (701.8–840.1 mg kg-1) sorbed more P than S1 (534.7–742.4 mg kg-1) with 0–5% biochar rate. Phosphate adsorption on biochar was satisfactorily described by the Langmuir equation (r2 = 0.97–0.99, P = 0.01) and Freundlich equation (r2 = 0.89–0.99, P = 0.01). Phosphorus sorption increased with biochar application rates (0–5%). Desorption experiment showed lower P release and suggests a partial or slow irreversibility of the adsorption–desorption phenomena upon biochar addition to soil. In fertilizer-applied soil (S2) loaded with 60 mg P kg-1 (as KH2PO4), desorption increased with increase in biochar application rates. Biochar application thus alters P availability depending upon P sorption and desorption capacities of soils which have implications for improving P use efficiency in soils. Keywords Biochar alkalinity, soil properties Sorption Desorption Red soil NPK Langmuir equation Freundlich equation Fertilizer
Introduction Phosphorus is an essential macro-nutrient and relatively less available than nitrogen and potassium in soil. In soils, bioavailability of added P is influenced by the nature of P sources, a range of soil properties (e.g., pH, variable charge surfaces particularly metal hydrous oxides, the presence of complexing compounds, and water-filled pore space), and plant root development [1]. Application of amendments like biochar is known to improve nutrient availability and soil properties and has the potential to combat climate & I. Rashmi [email protected] 1
Present Address: ICAR-Indian Institute of Soil and Water Conservation, Research Centre, Kota, India
2
ICAR-Indian Institute of Soil Science, Bhopal, M.P., India
change [2, 3]. Biochar is a stable solid carbon-rich product sometimes called as agrichar created by burning biomass in limited oxygen conditions [4] and remains in soil for thousands of years. Biochar is known to influence soil physical, chemical and biological properties. The greater ability of biochar to adsorb cations, due to greater surface area negative surface charge and charge density, makes it superior than many other types of soil organic matter [5]. Biochar addition influenced P availability and cr
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