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Liming Fields Does Not Harm Soil

Limestone powder with dendrite oxides may host toxins but most are not bioavailable

Madison, WI APRIL 19, 2011 – Liming soil is a common practice used in the agricultural process. Liming consists of spreading materials rich in calcium and magnesium onto fields in an effort to lower the soil acidity, and promote microbial functionality and plant growth. While the liming process does facilitate efficient crop growth, the limestone used to produce the materials may host highly increased concentrations of toxic trace metals. Brown and black dendrites often appear on limestone rock and consist of iron and manganese oxides. These fossil-like formations are prized by mineral collectors but little is known about their chemistry and the potential for these toxic metals to end up in the soil has yet to be explored.

 
Scientists at the Johannes Gutenberg University at Mainz, Germany, recently examined the mobility of arsenic and copper found in dendrites of a local limestone. They particularly measured the binding forms of the toxic metals at a molecular level using synchrotron radiation. Soil pots were limed and weekly values of arsenic and copper were taken to estimate the total amount released while the soil was completely waterlogged, a condition notorious for arsenic mobility.  
 
Results obtain through x-ray absorption spectroscopy techniques indicated that both arsenic and copper were strongly bound to their dendrite oxides. No changes were observed between the altered and the unaltered soil. Researchers conclude that the toxins would only be released if the oxide dendrites were to be dissolved, an extremely unlikely scenario in the agricultural world. Therefore, limestone powder used for agricultural liming poses no significant threat to soils since the copper and arsenic are not likely to become bioavailable.   
 
Michael Kersten, the author of the study, stated, “Current legislative codes based solely on threshold values are of little help in case of dendrite-rich limestone.  This research indicates that pollutant to iron or manganese ratios but not total pollutant amounts may be more useful in regulating the relatively harmless fertilizer impacts.”
 
Kersten’s research is ongoing to investigate more binding forms of pollutants. Other geographical and climatic regions need to be assessed with other types of toxic metal pollutants and fertilizers.
 
Results from the study are published in the March-April 2011 issue of the Soil Science Society of America Journal.

Soil Science Society of America Journal is the flagship journal of the SSSA. It publishes basic and applied soil research in soil chemistry, soil physics, soil pedology, and hydrology in agricultural, forest, wetlands, and urban settings. SSSAJ supports a comprehensive venue for interdisciplinary soil scientists, biogeochemists, and agronomists.

The Soil Science Society of America is an international scientific and professional society with its headquarters in Madison, WI. Our members are dedicated to advancing the field of soil science in relation to food production, environmental quality, sustainability, waste management and wise land use. We work at universities, government research facilities and private businesses across the United States and the world.