THE RELATION OF BUFFER CAPACITY AND ORGANIC MATTER TO THE SOLUBILITY OF THE NUTRIENT ELEMENTS IN TOA SILT LOAM

Abstract

1. Organic matter, buffer capacity, and the relation of changes in reaction to the solubilities of the mineral nutrient elements in six samples of Toa silt loam were studied. 2. The buffer characteristics may vary rather widely within a given soil type. The buffer curves for different samples of Toa silt loam show that the presence of larger amounts of organic matter markedly increases the buffer capacity near neutrality . This is reflected in the flatter buffer curves. The samples which contained lower quantities of organic matter are most highly buffered at the extreme ranges of high acidity and basicity. This is indicated by typical sigmoid buffer curves. 3. The state of the decomposition of the organic matter in these samples indicates as has been shown by previous work that the buffering effect of the organic matter is associated with the lignin-humus fraction. 4. Additions of acid to the soil increased the solubility of the nutrient mineral elements. The increases in the solubilities were greatest in the samples that were low in organic matter. 5. Although liming increased the amount of soluble calcium in the soil, it did not decrease the solubility of phosphorus. The additions of lime decreased the solubility of potassium. The solubilities of iron and manganese were too low to be easily measured above pH 7.2 and in only one case above pH 5.0. 6. Additions of acid to the soil increased the solubility of potassium when the reaction was forced lower than pH 5.0. There was a greater increase in the solubility of potassium from the acid treatments in the samples that were lower in organic matter. 7. The solubilities of iron and manganese were increased from additions of acid. Manganese became much more soluble than iron from increased acidity and its solubility was more affected in the samples that were low in organic matter.