Development and biomass yield of Soybean (Glycine max) and Pearl Millet (Pennisetum glaucum) in Lead contaminated soils

Abstract

Contamination of soil by heavy metals is of wide spread occurrence as a result of human activities such as mining and agriculture. Among the heavy metals, lead is a potential soil contaminant that readily accumulates in the soil. Due to increased demand for food security, lead contamination of soil has become a global issue and has gained considerable importance as a potent contaminant of agricultural soils. This study investigated the development and biomass yield of soybean and pearl millet grown in lead contaminated soils. Lead contaminated soils were collected from Kabwe's old Lead mine which had been in operation from 1902-1994 and diluted with uncontaminated soil from the field station. University of Zambia, School of Agriculture Sciences. The treatment concentrations were 0, 500, 1,000, 2,500 and 5,000 ppm extractable lead. Before planting, soils were characterized for pH, organic matter, texture, exchangeable bases, cation exchange capacity, total nitrogen, available phosphorus, total and extractable lead and microbial activity using standard laboratory procedures. Soybean (Magoye) and pearl millet (Lubasi) seeds were sown in a total of 5 kg of soil in pots. Plants were allowed to develop under greenhouse conditions. Growth was monitored and after 9 weeks of growth, nodule number (soybean), shoots and root length, and above and below ground biomass were determined. Shoot to root, shoot to total and root to total biomass were also calculated. Results indicated that lead contamination severely affected nodulation in soybean at all treatment levels except the control. The reduction in total plant biomass for 500, 1000, 2500 and 5000 compared to the control were 38.2, 58, 79.5 and 86.3% for soybean and 84.8, 86.1, 90.2 and 93.1% for pearl millet respectively, indicating that pearl millet growth was more adversely inhibited. Soybean root length reduced byl8.1, 27, 52 and 71% while pearl millet reduced by 35, 44, 27 and 42.5% respectively. A similar reduction trend was observed in shoot heights for both soybean and pearl millet. The result reflects that Lead is toxic to plant growth and development.

Key words: Heavy metal, lead contamination, biomass yield