Abstract
<p>This paper reports the findings of two studies conducted to investigate the effects on pH, Eh and sulfate content of sulfuric soil material of acid sulfate soil following the addition of organic carbon and nitrogen. The first study compared the responses to simple carbon sources (glucose, sodium acetate and molasses) with complex organic matter in the form of chopped<em> Phragmites</em>. The second experiment considered the effect of nitrogen by testing organic matter with varying nitrogen content. <span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">The results of the first study showed that the</span> changes in Eh and sulfate contents induced by these treatments mirrored the changes in pH, <span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;">the highest change being<span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"> only 5.6 units induced by sodium acetate</span></span>. These results showed that organic carbon alone was ineffective in treating sulfuric soil material acidity, and that nitrogen was needed. Lucerne hay which had the highest nitrogen content produced the largest increase in pH by 4.2 units, and the changes of pea straw and wheat straw was 3.2 units. It was proposed that the alkalinising effect of the treatments was mediated by anaerobic microbial metabolism which required sources of nitrogen as well as organic carbon. The changes in soil redox conditions by -150 mV measured indicated that sulfur-reducing bacteria induced the changes in Eh, which caused pH to increase and sulfate content to decrease in comparison with nitrate-reducing bacteria.<span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"> The findings of these<span style="font-family: TimesNewRomanPSMT; font-size: 9pt; color: #231f20; font-style: normal; font-variant: normal;"> studies have implications for management of sulfuric soil material acidity.</span><br style="font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px;" /><br class="Apple-interchange-newline" /><br /></span></p>
Highlights
Acid sulfate soils (ASS) are naturally occurring soils or sediments formed under reducing and water-logged conditions (e.g. Pons 1973, Simpson and Pedini 1985) that either contain sulfuric acid (H2SO4) or have the potential to form it, in an amount that can have serious negative impacts on the health of human and the environment (Buschmann et al 2008, Ljung et al 2009)
The pH measurement is the negative log of the hydrogen ion (H+) concentration and is the basis of determining whether a soil is acidic or alkaline so a choice of vegetation is made
The probable cause of these increases in pH occurred as a result of the aerobic microbial oxidation of the residual organic matter content (10.6%) that acted on it (Lambers et al 2009) and reduced the soil to Eh to near 0 mV
Summary
Acid sulfate soils (ASS) are naturally occurring soils or sediments formed under reducing and water-logged (anaerobic) conditions (e.g. Pons 1973, Simpson and Pedini 1985) that either contain sulfuric acid (H2SO4) or have the potential to form it, in an amount that can have serious negative impacts on the health of human and the environment (Buschmann et al 2008, Ljung et al 2009). Pons 1973, Simpson and Pedini 1985) that either contain sulfuric acid (H2SO4) or have the potential to form it, in an amount that can have serious negative impacts on the health of human and the environment (Buschmann et al 2008, Ljung et al 2009). Release of the sulfuric acid produced in turn leads to solubilisation of soil matrices in which potentially toxic constituents (metals and metalloids) are held (Fitzpatrick et al 2008). Production of sulfuric acid, mobilisation and accumulation of toxic soil constituents, e.g. Fe and Al, coupled with deoxygenation, and production of monosulfidic black ooze are the major causes of the negative impacts of ASS on the environment (Michael 2013)
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