Agricultural Impacts of Coal Mine Subsidence: Effects on Corn Yields

Undergronnd coal mining methodology is moving toward techniques that cause immediate planned subsidence of the overlying land. Damage done by subsidence to structures has been documented, but the effects on agricultural productivity are undocumented. This study was conducted to (i) determine the extent of measurable subsidence effects associated with planned subsidence mining, (ii) measure the impact of subsidence on corn (Zea mays L.) yield, and (iii) compare the effects of longwall and high extraction retreat mining methods. Five locations in southern Illinois were included in the 3 yr of the study. A total of 4605 ha in 1985, 6747 ha in 1986, and 7764 ha in 1987 were involved. These areas represented unmined control areas as well as longwall (LW) and high extraction retreat (HER) types of mines. Aerial photographs of the study locations were taken in the spring of each year. Subsided areas were identified, classified, and measured on the photos. The average percent of the study urea with measurable subsidence effects was 7.5% for LW mining and 3.3% for HER mining. Corn was harvested each year on selected subsided and nearby unsubsided reference areas. The weighted average reduction in corn yield on land above the mines was calculated by multiplying the affected area by the associated yield reduction. The weighted average yield reduction was 4.7% for LW mining and 1.8% for HER mining. Results for the individual years varied with the weather: the greater the precipitation, the greater the yield reductions. The results also reflect the yearly variation in mining activity, crop sample areas, and overall study areas. In addition, the mitigation of subsidence effects in place at the time of the study also influenced the results, but the potential for mitigation for either mining type was not included in the research. Contribution of the Agric. Exp. Stn., College of Agriculture, Univ. of Illinois, Urbana, IL 61801.