Copper levels in soils collected from cofffee farms along Ruiru river in Kiambu district and Rutui river in Kirinyaga district

Abstract

The total copper content was determined in river water, sediments, soil, potato shoots and tubers, weeds, coach grass, coffee leaves and coffee berries using atomic absorption spectrophotometry (AAS). Plant available copper in the soil was also determined using AAS and the values obtained compared with the copper content in coach grass. coffee leaves and coffee berries. Also compared was the total copper and the EDTA extractable copper (plantavailable Cu) content in the soil. The variation oftotal copper content in the soil with time. depth and rainfall was studied. This study was done in a garden where a known quantity of a copper based fungicide had been sprayed on the soil surface. The values obtained in river water showed no significant poLlut.Lon and the same was true of the potatoes analysed. AAS was chosen for all analysis due to its convenience both "timewiseand economically. Analysis of certified samples proved the AAS technique to be accurate. Soils from Kirinyaga District had ahigher copper content than those from Kiambu District. Soils from Kirinyaga had copper levels ranging between 25 ppm and 527 ppm while those from Kiambu had levels ranging between 9ppm and 140 ppm. Plant available copper content was found to be proportional to the total copper content in the soil. River water from the two regions had a low copper content ranging between 4 parts per billion and 20 parts per billion. For potatoes. the peels had a higher copper content than any other tissue. Inthe case of coffee leaves and beans, leaves had a higher copper level than the beans. Generally for plants, the copper content ranged-between 2 parts per million and 200 parts per million.