Towards a Single-Point Approach for Estimating Potassium Quantity-Intensity Parameters in Soils at Different K Saturatio
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ORIGINAL PAPER
Towards a Single-Point Approach for Estimating Potassium Quantity-Intensity Parameters in Soils at Different K Saturation Ratios Fotis Bilias 1 & Nikolaos Barbayiannis 1 Received: 16 January 2020 / Accepted: 17 March 2020 # Sociedad Chilena de la Ciencia del Suelo 2020
Abstract The objective of this study was to obtain sufficient estimates of quantity-intensity (Q/I) parameters using a single-point method, and to evaluate the role of cation exchange capacity (CEC) and Gapon selectivity coefficient (KG) as parameters that improve prediction model’s estimation accuracy or explain its limitations under conditions of K deficiency. Regression models were applied on raw data derived from previews Q/I experiments conducted on 20 soils of northern Greece at initial and K-depleted treatment states. Relationships between soil K adsorbed or released (ΔΚ), or K activity ratios at each K addition (ARK) and respective values at equilibria (-ΔΚ0, AReK) were tested to find the best fitting models. CEC was included in regression models to improve their performance, while KG parameter was assessed for initial and K-depleted soils. The study showed that Q/I parameters were well predicted with the single-point method for a wide range of K saturation ratios, by applying 0.01 M CaCl2 and 10 mg L−1 K addition. Furthermore, CEC significantly improved model’s estimation accuracy. Under the ΔG breakpoint of − 14.67 kJ mol−1, specific adsorption sites of the soil inner-sphere region weaken the single-point prediction efficacy, as was clearly indicated by the KG formation under conditions of K depletion. The study suggests that the proposed method is applicable for estimating Q/I parameters for soils covering a wide range of K activity ratios. Moreover, CEC and KG parameters constitute useful tools in improving prediction model’s estimation accuracy, or explaining their limitations under conditions of K deficiency. Keywords Quantity-intensity . Single-point Q/I prediction . Potassium dynamics . Non-exchangeable K . Cation exchange capacity
1 Introduction Quantity-Intensity concept (Q/I), as a specialized version of sorption curves experimentation for describing potassium potential buffering characteristics, has been firstly introduced by Woodruff (1955a, b) and further developed by Beckett (1964a, b), in an attempt to describe the mechanisms of K release and fixation from soil solid phase to soil solution. Until now, almost seven decades after these first approaches, and although that the universality in scope in predicting soil available K has often been questioned, quantity-intensity experiments still remain one of the basic tools in elucidating K dynamics in soils. * Fotis Bilias [email protected] 1
Soil Science Laboratory, Soil Science and Agricultural Engineering, Aristotle University of Thessaloniki, Thessaloniki, Greece
The latter explains why lots of recent published research dealing with potassium dynamics are still addressing K availability issue under the Q/I concept perspective (Das et al. 2019; Islam et al.
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