Atmospheric Deposition and Heavy Metal Contamination in an Organic Farming System in a Seasonally Dry Tropical Region of India

Increased consciousness about agricultural sustainability and health risks associated with agrochemicals has lead organic farming to be a globally emerging alternative farm practice. We report the effect of atmospheric deposition on soil quality and heavy metal contamination of agricultural produce under an organic farming system using wheat and corn as test crops. Data obtained in the open field (OFO) were compared with a plastic-covered glass-house-grown system (OFG). The results showed that depositions of Cd, Cu, Ni, Pb, and Zn increased with time. Soil porosity, water holding capacity, microbial biomass carbon (Cmic), substrate-induced respiration (SIR), alkaline phosphatase, and FDAase activity decreased, whereas the bulk density and contents of Cd, Cu, Ni, Pb, and Zn increased over time in open plots receiving atmospheric deposition. Concentrations of metals in grains in OFO crops exceeded the safe limits of Indian standards and were three to sixfold higher than those recorded in OFG plots. These results indicate that atmospheric deposition of heavy metals can have a destabilizing effect on soil fertility in organic farming and can greatly increase the dietary intake of toxic metals. This may have long-term implications for human health as well as for agricultural sustainability. The data presented here have particular concern for developing countries, where unprecedented urban-industrial growth and consequently increased input fluxes of heavy metals will continue for decades to come.