Effects of Pyrolysis Conditions on Leaching of Salts from Halophyte Biochars

Abstract. Among the options for restoring salt-affected arable land are irrigation with fresh water to leach salts below the root zone and planting crops that will uptake salts (phytodesalination). Understanding salt availability in halophyte biomass, and in biochars made from that biomass, will lead to new methods for restoring crop growth potential for salt-affected soils, especially in arid regions with alkaline and calcareous soils. The objectives of this project are to identify the mechanisms by which pyrolysis converts certain salts into less leachable forms, and to quantify the amount of salt that can be removed from soils and immobilized in biochars. In this first study, biomass from two Atriplex species, A. lentiformis, or big saltbush, and A. canescens, or four wing saltbush, were treated by slow pyrolysis at 400-600°C and the biochars produced were leached with water using a constant head permeometer. Cations left in the solids and the leachates were quantified and used to construct salt mass balances. Early results indicate that calcium and magnesium are retained in biochars more than sodium and potassium, that A. lentiformis biochar contains more salt but retains a lower fraction of that salt than A. canescens, and that salt retention in biochar is dependent on both biomass species and pyrolysis temperature.