Positive and Negative Effects of Addition of Organic Carbon and Nitrogen for Management of Sulfuric Soil Material Acidity under General Soil Use Conditions

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 Phragmites. The second experiment considered the effect of nitrogen by testing organic matter with varying nitrogen content. The results of the first study showed that the changes in Eh and sulfate contents induced by these treatments mirrored the changes in pH, the highest change being only 5.6 units induced by sodium acetate. 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. The findings of these studies have implications for management of sulfuric soil material acidity