Plant-soil interactions of sludge-borne heavy metals and the effect on maize (<i>Zea mays</i> L.) seedling growth

Abstract

The use of sewage sludge as an organic fertiliser under South African conditions is an alternative disposal route to sacrificial land disposal. However, the lack of research done under South African conditions and the conservative nature of the heavy metal guidelines, when interpreted as total metal content is limiting the agricultural use of sludge. A glasshouse experiment, which forms part of a greater project, was conducted to characterise soil-plant interactions of the main sludge-borne heavy metals (Pb, Cd, Zn and Cu) in two sludges (low metal and high metal) to different soil types (clayey, loamy and sandy) on maize seedlings. Growth differences, heavy metal accumulation in plant parts and soil-metal concentrations (total and potentially available) were determined. The low metal sludge treatment showed the highest yield for maize seedlings when compared to controls (soil unamended and inorganic fertiliser added). The amendment of sludge to the soil did indicate higher heavy metal content, although the increase was not as predicted, owing to the difficulty of obtaining a representative sample in the soil. Except for Cd, heavy metal values in the soils (at the beginning and end of experiment) exceeded guidelines due to very high background values in the soil. No negative effects of heavy metal contamination in plant parts of the crops could be proven. Results showed that application of sludge to different soils could be useful in order to increase crop growth over a 28 d period in the glasshouse. Soil, plant and water quality monitoring, together with the prevention of metals entering the plant, is a prerequisite in order to prevent potential health hazards of sludge application to agricultural land.

Effects of treated sewage sludge levels on temporal variations of some soil properties of a Typic Xerofluvent soil in Menemen Plain, Western Anatolia, Turkey

“…pH and CaCO 3 values were determined between 7.6-7.85 and 2.52-2.58%, respectively. It is recommended that soil pH should be maintained above 6.5 for sludge-amended soils (Henning et al 2001). Smith (1994) noted that optimal pH value for growth of the majority of plants was between 6.5 and 7.0.…”

Long-term impacts of pasture irrigation with treated sewage effluent on nutrient status of a sandy soil in Zimbabwe

“…Mobility could also have been enhanced by high hydraulic loading of approximately 4500 mm ha -1 yr -1 . A study conducted by Henning et al (2001) on a sludge-amended sandy soil showed higher Cd concentrations in control than sludge-mended soils due to Cd mobility. Kabata-Pendias and Andriano (1995) also reported trace metal mobility on acid sandy soils of low organic matter.…”

“…Bray-1 P was extracted by Bray-1 method and determined as for total P. Exchangeable cations were extracted by acidified ammonium acetate followed by atomic absorption spectrophotometric determination for Ca and Mg, and flame emission for K and Na. Zn, Cu, Cr and Cd were extracted using the USEPA double acid digestion method which recovers almost 100% of the metals from the sample (Henning et al 2001). Samples were weighed, ashed and taken up in HClO 4 -HNO 3 solution and made up to a known volume.…”

Identification of Cu and Ni indicator plants from mineralised locations in Botswana

“…In order to evaluate metal translocation from the soil to the shoots, i.e., find out how much of the total metal concentration in the soil the plant actually took up and transferred to the shoots, an operationally defined transfer coefficient (TC), also known as transfer function (Adriano, 2001;Henning et al, 2001), was calculated. It is defined as the ratio of the metal concentration in the plant [M] plant to the total metal concentration in the soil [M] soil (Adriano, 2001;Henning et al, 2001).…”