Accumulation of lead and nutrients in soybean and sorghum cultivated in lead-affected tropical soils

Abstract

Lead is a potentially toxic chemical element, being responsible for many deleterious effects in living organisms. Therefore, understanding its dynamics and influence on plant growth is relevant for food security. The influence of Pb doses on nutrient accumulation in sorghum and soybean in two tropical soils with different buffering capacities was tested in a greenhouse study with four independent experiments (one per species/soil combination). The hypothesis was that the presence of Pb in soil decreases the accumulation of nutrients in soybean and sorghum plants. Soybean cultivated in a Typic Hapludox (TH) and sorghum, cultivated in both a Rhodic Acrudox (RA) and a TH, received 0, 200, 400, 800, 1200, 1600, 2200, and 2800 mg/kg of Pb, while soybean cultivated in RA received 0, 200, 400, 800, and 1600 mg/kg of Pb. Seeds were sown 24 h after application of Pb. Plants were harvested 21 days after the emergence of at least 50% of plants from the control treatment (approximately 30 days in total). Lead, macro, and micronutrient contents were determined in the shoot dry matter (SDM), and bioavailable Pb in soil was assessed by Mehlich-1. In general, TH allowed greater Pb uptake by plants, due to its lower buffering capacity. Soybean was the most affected crop with decreasing concentrations of N, K, Mg, and Ca, the latter was especially affected, with deficiency symptoms being observed. Effects on a longer time-scale are unknown, since significant decreases in nutrient contents were observed.