Heavy metal contents of some soils of tomato growing fields in Hai district, Tanzania, as influenced by duration of use of metal-containing fungicides

Abstract

Hai district is one of the major vegetable producing areas of Tanzania. Copper fungicides have been used for a long time in the district, but no studies have been conducted to evaluate accumulation of Cu in the soils in that district. This study was, therefore, initiated-to survey and-to document the status of  fungicide use in some tomato fields. Generally, the total or DTPA extractable Cu contents were significantly (P < 0.05) higher in fungicide-treated, soils than in control soil, the levels reaching 7305 mg total Cu/kg soil where fungicides have been used for 15 to 30 years (long-term use).  The total and extractable  Cu contens of the  soils increased with increasing duration of Cu fungicide use. This resulted in lower microbial populations with increasing duration of fungicide use, the populations decreasing from log₁₀ = 6.4 in control soils to log₁₀ = 5.1 in long-term use soils, Zinc and manganese did not show clear trends. There was no significant relationship between total or DTPA-extractable Cu, Zn or Mn and soil pH. Total Cu was significantly and positively correlated with organic carbon, while total Mn was significantly but negatively correlated with organic carbon. It is conclud that long-term use of Cu fungicides in Hai district has resulted in a build-up of Cu residues in the soils, and this may impair microbial processes in those soils.

Keywords: heavy metals, pollution, heavy metal-containing fungicides, tomato microbial populations

Tanzania . J. Agric. Sc.(200l) Vol. 5 No. 1, 1-8