Soil organic matter is quite important as a source of cation‐exchange capacity in Coastal Plain soils. The amount of organic matter in well‐drained soils is directly related to the clay content. In the very poorly drained soils this direct relationship was not apparent. The cation‐exchange capacity of soil organic matter varied from 62 to 279 me. per 100 g. The nature of the exchangeable hydrogen of organic matter was measured by the use of several replacing solutions. A portion of the exchangeable hydrogen in soil organic matter was found to come from strong acid groups.

Three particle size ranges of calcitic and dolomitic limestones were applied at 4.5, 9, and 13.5 metric tons/ha. Evaluations were designed to determine the most efficient treatment for neutralizing soil acidity, and increasing crop production in Katy fine sandy loam (pH 5.2) and Boy loamy fine sand (pH 5.4). Liming effects were evaluated by soil and plant analyses. Efficiency rating (ER) was used to describe the limestone particle size ranges. Finer limestone particles were assigned higher relative efficiency values. The sum of the products of particle size percentage ranges multiplied by the relative efficiency assigned those ranges, times the neutralizing value of that limestone is the ER.Increases in soil pH were proportional to limestone ER and application rate. Calcitic limestone neutralized soil acidity more rapidly than did dolomitic. We found a statistically significant increase in calcium (Ca) in the 30‐ to 46‐cm depth of Boy loamy fine sand at the 13.5 metric ton/ha rate of ER 110 calcitic limestone. This was probably due to 689 kg of N/ha applied as NH4NO3 the first year following limestone treatment. Magnesium (Mg) increased in the 30‐ to 46‐cm depth due to all dolomitic treatments.Limestone did not increase the yield of corn (Zea mays L.) or Coastal bermudagrass (Cynodon Dactylon L. Pers.) in the harvest year.All treatments of calcitic limestone significantly increased the Ca percentage in corn. All dolomitic limestone treatments except the ER 26 material applied at 4.5 metric tons/ha increased Mg concentration in corn leaves and Coastal bermuda‐grass. Manganese toxicity occurred in corn plants growing in nonlimed plots the third season following treatment. Soil acidity and reducing conditions contributed to the toxicity.

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Synopsis Nitrate‐N production appeared to give a better estimate of the availability of soil N than Kjeldahl N or organic matter. Higher correlation coefficients were obtained for data from well‐drained than from poorly drained soils. Comparisons between results for organic matter or Kjeldahl N and corn yield responses from N applications under field conditions were not significant.