Biochars reduce irrigation water sodium adsorption ratio
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ORIGINAL RESEARCH
Biochars reduce irrigation water sodium adsorption ratio Saima Awan1 · James A. Ippolito2 · J. L. Ullman3 · Kamran Ansari1 · Liqiang Cui2,4 · A. A. Siyal1 Received: 27 July 2020 / Accepted: 7 October 2020 © The Author(s) 2020
Abstract Irrigation water quality plays a vital role in sustaining crop productivity and feeding a growing world population. In many countries, continued agricultural water reuse can lead to greater water-soluble salt concentrations, and in particular Na; finding means by which irrigation water Na, and thus sodium adsorption ratios (SAR), can be reduced would reduce the rate at which soil sodification occurs. Four biochars, containing a variety of organic functional groups and electrochemistries, were examined for their potential to sorb and remove Na from simulated irrigation water, and subsequently reduce water SAR. Two batch experiments examined the role that wheat straw biochar, lodgepole pine biochar, Kentucky bluegrass biochar, and hemp biochar played in terms of sorbing sodium over time or application rate. Of the four biochars examined, hemp biochar had the lowest oxidation–reduction potential (ORP; ~ 0–100 mV), sorbed the greatest Na amount (up to 923 mg kg−1), and released Ca and Mg (up to 115 and 63 mg kg−1, respectively) into solution, all of which led to a significant reduction in water SAR (from 8.8 to 7.3; 17% decrease). Sodium sorption onto hemp biochar better fit a Langmuir versus a Freundlich isotherm, yet followed a pseudo-second-order model better than a pseudo-first-order kinetic model. The data suggest that Na ions formed a monolayer on the hemp biochar surface, influenced by associations with π electrons, but given time the Na ions may diffuse into biochar pores or more slowly interact with biochar-borne π electrons. Hemp biochar shows promise in reducing the SAR of Na-impacted waters. Future investigations should focus on additional laboratory, greenhouse, and field trials with hemp biochar and other biochars designed to have similar or superior properties for sorbing excess irrigation water Na and improving crop growth. Keywords Biochar · Na-containing irrigation water · Oxidation–reduction potential · Sodium sorption · π Electrons
1 Introduction Clean water is arguably the most important natural resource for fulfilling basic life requirements, yet clean water is under constant threat globally. The present world population is projected to be 8.6 billion by the year 2030, 9.8 billion by
* James A. Ippolito [email protected] 1
US‑Pakistan Center for Advanced Studies in Water, Mehran University of Engineering and Technology Jamshoro, Sindh 76090, Pakistan
2
Department of Soil and Crop Sciences, Colorado State University, Fort Collins 80523, USA
3
Department of Civil and Environmental Engineering, University of Utah, Salt Lake City 84112, USA
4
School of Environmental Science and Engineering, Yancheng Institute of Technology, No. 211 of Jianjun Road, Yancheng 224051, China
2050, and 11.2 billion by 2100 (United Nations 201
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