Soil acidification and sawdust amendment effects on rabbiteye blueberry growth, and the effects of acidification on soil properties

Aluminum sulfate (Al₂(S0₄)₃) and elemental sulfur (elemental S) at four rates each were used to acidify a sandy loam soil to various levels of soil acidity. Aluminum sulfate was applied at rates of 7.5, 15.0, 30.0,and 60.0 grams per pot (3000, 6000, 12,000, and 24,000 kg/ha, respectively), while elemental 5 was added at rates of 1.9, 3.8, 7.5, and 15.0 grams per pot (750, 1500, 3000, and 6000 kg/ha, respectively). Sawdust was incorporated into the soil at rates of 0, 20, 40, and 60% by volume. In the first part of this investigation, the two soil acidulents were evaluated for their potential to produce optimal growth in rabbiteye blueberries (Vaccinium ashei) through lowering of soil pH. The greatest plant weight gain was achieved using elemental S at 7.5 grams per pot, and 60% sawdust, which acidified the soil to pH 4.4. At the highest rates of application of both acidulents, plant weight gain decreased considerably from the optimum, suggesting that a toxicity may have existed. Growth was severely reduced where no sawdust was amended into the soil, regardless of the source or rate of acidulent. In the second part of this investigation, the acidulents were compared for their effects on several soil properties. These soil properties included silver-thiourea extractable Ca, Mg, K, Na, A1, and H, plus CEC, pH, and mineralogy. Magnesium and Ca levels in the most acid treatments were approximately double those of the controls and appeared to be the result of the amount of decrease of pH, rather than the source of acidulent. Potassium levels were substantially higher in the high elemental S treatments than in the controls, apparently as a result of destruction of hydroxy interlayered vermiculite (HIV) and a subsequent release of K in this treatment. Sodium levels differed from the controls only in the Al₂(S0₄)₃ treatments, where they increased with increasing rate of application. Aluminum and H levels increased sharply only at the highest rates of application of both acidulents. Much of this effect was pH related. In addition to being more favorable for plant growth, 1 unit weight of elemental S was found to cause the same pH decrease as approx-imately 8 times as much Al₂(S0₄)₃. Sawdust levels had no significant effect on the amount of decrease in pH. Destruction of clay minerals was evident in DSC patterns at the highest rate of elemental S application. Clay minerals that showed alteration were gibbsite, kaolinite, and HIV. This destruction of clay minerals, however, led to increases in Ca/Mg and K/NH₄ CEC values, when compared to the controls. These increases are thought to be a result of creation of more edges or exposure of interlayer of HIV.