| dc.description.abstract | Copper fungicides are intensively applied on Coffea
arabica L. in Kenya to control coffee berry disease (Colletotrichum
coffeanum Noack) and leaf rust (Hemileia vastatrix
Berk. & Br.) and to induce vigorous growth (tonic effect). It
is thought that this continual use of Cu could increase Cu
levels in the soil to an extent where the nutrition and growth
of coffee would be affected. To study this possibility,
experiments were carried out in the field in coffee plantations,
some of which had been sprayed with Cu fungicides for over 5
years, whereas others had never been sprayed. Experiments were
also conducted on young coffee seedlings in greenhouse to
study both the effects of increasing Cu'concentrations on plant
growth and also the extent to which such factors as pH and P
fertilization could influence the uptake of Cu by the coffee
plants.
The field studies .howed soil Cu concentrations greater
than 10 ppm in the regularly Cu-sprayed coffee plantations,
whereas soil Cu values in the uns rayed plantations were lower
than 3 ppm Cu. These levels of soil Cu, however, did not
produce severe nutritional disorders in the coffee plants,
although scattered signs of·interveinal chlorosis and yellowing
were observed in the leaves of the Cu sprayed ptants; High m leaf-and-bean- Cu were also associated with increased Cu spray
and in soil available Cu. The absence of pronounced Cu toxicity
symptoms in the field at this stage, is thought to be due to
the high level of soil-organic matter, and heavy fertilization
with phosphate both of which contribute to Cu fixation in the
soil. Also the strong accumulation of Cu in the top-soil may
have contributed to this by rendering Cu unavailable for
absorption by the deeper roots of mature coffee plants.
Experiments in soil, in sand and in water culture with
young coffee plants (in the greenhouse) showed that Cu treatments
greater than 1.064 ppm in the water and sand cultures, and
greater than 5 ppm in the soil culture, resulted in stunted
plant growth, severe necrosis of roots and leaves and hindrance
of nutrient translocation. Effects of high Cu in the medium
were most marked in acid soils (pH 4.5-5.0), and less pronounced
in moderately acid (pH 5.5-6.0) and neutral (pH 7.0-7.5) soils.
Phosphorus treatments, from 140 to 240 ppm P, and Cu
treatments at 1.064 ppm Cu in sand culture, separately promoted
plant, growth compared to the control treatment. The increase
in growth, at 1.064 ppm Cu and at 140 ppm P, over the control
plants, grown in the complete nutrient solution, showed that
the original levels of Cu (0.064 ppm) and P (40 ppm) in the
solutions were inadequate. Nutrient-P levels of 140 - 240 ppm
in combination with high Cu levels, (10.064 - 100.064 ppm Cu),
caused severe reduction in plant growth. At high P levels
(440 - 840 ppm P) in the presence of low Cu levels (less than
1.064 ppm tu), a decrease in leaf-Ca and-Mg, an' increase in leaf-K
and severe chlorotic symptoms in the leaves were observed. The
increase in 1eaf-K was undoubtedly due to the additonal K
supplied (to the nutrient solution) by the P-carrier (KH2P04).
At medium toxicity levels of Cu, increased P levels tended to
reduce the Cu toxicity effects on the plants, but at severely
toxic levels of Cu, the addition of heavy doses of P was
ineffective. Significant Cu x P interactions occurred for the major nutrients in the leaves whereas there was a high
accumulation of most of the trace elements and P in the roots
at high Cu and P treatments. Anatomical observation on the
leaves and roots of plants affected by high Cu absorption
revealed severe cell destruction and abnormalities in the
cellular structures. -Increasing the pH of acid soils to near
neutrality and the application of P-fertilizers reduced the
high Cu effects. | en |
