Since the CMS products have considerably more nutritive value than peat or the other materials, the results suggest that in this experiment, the improvement of soil physical characteristics was more critical than improvement of soil fertility. This is not surprising, given the very wet year we had in Columbus, and the naturally high level of fertility present in the research field soil. Given a sandy, poor soil, we might expect to see the composts out-perform the peat. However, soil pH was increased by as much as 1.1 unit by compost addition. Soil pH was decreased by at least a full unit in the peat-amended plots compared to unamended field soil.
Elemental sulfur is oxidized to sulfuric acid by microorganisms in the soil.
The sulfuric acid releases sulfate ions in the soil, which contribute to soluble salts. While the effect of sulfur on soil EC was highly significant, no detrimental effect on growth was observed. The highest soluble salt level attained was 1.0 mmhos.cm, which should not injure plants. By August, the average pH was 0.6 units lower than minus-sulfur treatments. While the soluble salt and pH effect of the composts were not critical growth factors in this experiment, the evidence that composts may significantly increase soil pH and EC may be important should we try to grow plants such as azaleas and rhododendrons in soils that are borderline for their growth.