A calorimetric assessment of the effects of sodium chloride and sodium bromide on the microbiological and thermokinetic characteristics of soil

Abstract

Excess salinity may lead to degradation of arable land and exclusion from agricultural production by worsening of their properties. The evaluation of the characteristics of saline soils is very important from the point of view of the use of agricultural soil. The aim of this study was to determine changes in the physicochemical properties of soil, the content and activity of soil microbial biomass (SMB) and the thermokinetics of glucose biodegradation in soil samples containing different doses of sodium chloride and sodium bromide (0.0263; 0.0526; 0.1052; 0.1578; 0.2104; 0.2630mmolg−1 DM soil), and to compare the effects of both salts. The pH values of soil samples decreased (from 6.1 to 5.4 for NaCl and NaBr) and electrical conductivity increased (from 0.20dSm−1 to 2.61dSm−1for NaCl and 2.30dSm−1 for NaBr) with increasing doses of both salts. SMB content, determined based on substrate-induced respiration (SIR), decreased with increasing doses of NaCl and NaBr (from 737mg C to 348mg C for NaCl and 379mgCkg−1 DM soil for NaBr). Both salts inhibited glucose biodegradation processes in soil proportionally to their increasing doses (NaBr exerted a greater inhibitory effect). This was confirmed by lower values of the maximum rate of heat production (RHPmax) and the apparent growth rate constant (k), and by higher values of peak time (PT), generation time (tG) and the inhibitory ratio (I). Changes in pH, SIR-SMB and Qtmax (total heat production) were modeled based on the applied doses of NaCl and NaBr. The empirical data were well approximated by the proposed mathematical models representing relationships between soil pH, SIR-SMB and Qtmax vs. the applied doses of NaCl and NaBr. They can be used to reliably predict the effects of the analyzed salts on the tested soil parameters.