Effects of fungicide use on coffee and vegetables on the status of copper and other heavy metals in soils of Lushoto Dstrict, Tanzania
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Date
1997
Authors
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Journal ISSN
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Publisher
Sokoine University of Agriculture
Abstract
This study was conducted with the general objective of quantifying the
accumulation of Cu and other heavy metals in coffee and vegetable growing
soils of Lushoto district, Tanzania, as a result of continual use of fungicides
for the control of coffee and vegetable diseases. The study involved analysis
of soil samples taken from coffee and vegetable fields sprayed with fungicides
for different durations of time and from control soils where spraying did not
take place. Copper, Zn and Mn were extracted using 0.005M DTPA while
total quantities of the heavy metals were extracted using aqua regia.
The results indicated that in vegetable fields DTPA-extractable Cu and Zn in
the top (0-5 cm) soil increased from an average of 4.3 and 9.8 mg/kg,
respectively, in farms that had never been sprayed with fungicides to 52 and
12 mg/kg in famis which have received fungicides for more than 20 years.
Total Cu and Zn increased from an average 44 and 63 mg/kg in famis which
had never been sprayed with fungicides to an average of 175 and 83 mg/kg,
respectively, in fields wliich had received fungicides for more than 20 years.
In coffee fields DTPA-extractable Cu and Zn increased from an average of 3.2
and 5.2 mg/kg in control soils to an average of 81 and 41 mg/kg in fields
received fungicides. Total Cu and Zn increased from an average of 51 and 50iii
mg/kg, resjxjctively, in control soils to an average of 255 and 205 mg/kg in
fields sprayed for a more than 30 years.
Comparison of metal contents in coffee and vegetable fields revealed that in
both coffee and vegetable fields Cu and Zn contents differed from one site to
another and that fields sprayed for prolonged period of time contained elevated
amounts of these elements.
Effect of the duration of use was found to be significantly (P=0.05) different
between different categories especially Cu and Zn while, Mn was found not
to be related to the duration of fungicides use.
Heavy metal contents were found to significantly (P=0.05) correlate with some
selected soil properties, especially organic carbon.
It was concluded that spraying coffee or vegetables with copper fungicides
increased the amount of Cu and Zn in the soil. Fungicide use did not result in
increased amounts of soil Mn.
Distribution pattern within the plowlayer and metal contents within the
individual farms were found to be closely related to duration of application,iv
ly]3e of fungicides used, degree of management within the individual farms,
and nature of the topography especially in coffee farms.
It was also concluded that organic matter contents played a major role in
controlling the concentration of heavy metals in both coffee and vegetable
fields.
Description
Dissertation
Keywords
Vegetable growing soils, Vegetable diseases, Lushoto district