MARL IN THE COASTAL PLAIN OF NORTH CAROLINA: FROM AGRICULTURE TO AQUACULTURE

In the 19^th century, the southern United States had an economy dominated by agriculture, primarily cotton, corn, peas, and tobacco. Limited crop rotation and the heavy demands these crops placed on the poor soils caused depletion of essential nutrients and harvests waned. Farmers recognized the need to enrich the soils, and marl was used as a cheap fertilizer. Geological studies by Benjamin Silliman in New York showed how this poorly-to-well-consolidated calcareous mudstone/limestone was readily available and easily obtained. In North Carolina, Denison Olmsted and Elisha Mitchell (students of Silliman) focused on minerals of practical utility. Large deposits of marl were found in the midland and eastern counties, and were immediately used in agriculture. The poor soils of the Coastal Plain benefited greatly from marl’s effects, neutralizing the acidity, increasing soil moisture, and providing replenishing nutrients. Paired with other fertilizers such as manure, marl allowed for the full potential of the soil to produce with great quantity and quality. Knowledge of marl spread to South Carolina and Virginia where Edmund Ruffin evaluated this natural resource for agricultural purposes, and conducted the first South Carolina agricultural survey (1842). Marl was mined in open pits, but could be difficult to process depending on the induration. Marl mining was expensive in terms of excavation and transportation, and produced some early environmental issues by the 1900’s. With large-scale, mechanized farming, the need for cheap fertilizer became important. By 1910, man-made nitrogen fertilizer and synthetically manufactured ammonium sulfate were readily available. By the 1970’s fertilizers were either synthetic or obtained from cheaper foreign sources and marl’s time had come and gone.

In the late 20^th century, aquaculture became an important economic resource for North Carolina, specifically the Pamlico Sound area. However, overharvesting of oysters has resulted in research (2002) to improve their populations. In early 2010, marl has been placed into the sound to provide a solid substrate to allow growth and development of oysters in a reef-like habitat. Although the mundane use of marl in agriculture has waned, in this new age of aquaculture, marl can still be considered an important economic resource for the southeastern United States.