Variation of Mineral Micronutrient Elements in Robusta Coffee (Coffea canephora Pierre ex A. Froehner) As Measured by Energy Dispersive X -Ray Fluorescence | Chapter 12 | Recent Advances in Biological Research Vol. 4
Introduction:
In many parts of the world, Coffea grows between latitude 25°N and 25°S and
requires specific climatic conditions to produce high bean yield and quality.
In Uganda, Robusta coffee is grown in a diversity of soils that range from red
sandy clay or gravelly loam to soft laterite. Macro-elements such as K, Ca and
Na though detectable through EDXRF are not as heavy as trace elements such as
Fe, Zn, Cu, Mn, a factor that makes the micro-elements more amenable to EDXRF
measurement. The EDXRF spectrometer instrument has a semi-conductor detector
that measures the entire energy spectrum when placed closer to the sample to
minimize loss of energy by the fluorescent X-ray.
Aim:
Robusta coffee growing countries of the world such as Uganda, have experienced
a decline in market prices since 2002 due to changed consumer preferences for
other beverages. In Uganda, where Robusta coffee is the major income earner,
one practical way of ensuring that coffee prices remain competitive is to
enhance quality. The aim of this study was to analyze the extent of macro and
microelement densities in the soils of Robusta coffee growing Ugandan farms,
their relationships with density levels in the leaf and in the green bean and
their ultimate contribution in the determination of cupping and marketing
qualities. This information would enable coffee producers in Uganda to make
decisions on which organic and inorganic fertilizer applications are needed to
alleviate coffee quality which in turn is the key determinant of world prices.
Study
Design: Soil, leaf and ripe cherry samples
were derived from sixty seven tagged trees in twenty three on farm locations at
Kawanda and Entebbe in fields that had no fertilizer application history.
Place
and Duration of the Study: This work was conducted at the
National Agricultural Coffee Research Institute (NaCORRI), Uganda and the
Institute of Nuclear Science and Technology, University of Nairobi, Kenya,
between January 2010 and December 2013.
Methodology:
Nutrient densities of potassium (K), calcium (Ca), iron (Fe), titanium (Ti),
zinc (Zn), copper (Cu), boron (B), lead (Pb) and manganese (Mn) of sixty seven
soil, leaf and green bean samples collected from 23 districts were measured
with Energy dispersive x-ray fluorescence (EDXRF). All the samples were
oven-dried at 800C for 18-20 hours and ground to about 50 mm sieve-size. Three
pellets of 2.5 cm in diameter were made and irradiated with a Cd-109
radioactive source. The X-rays emitted by the elements were detected by liquid
nitrogen cooled Si (Li) detector and data analyzed with the Quantitative X-ray
Analysis System (XQAS/AXIL) software.
Results:
The results showed that the mean concentrations of Ca, Mn, Fe and Zn were
highest in the soil but lowest in green beans. K concentrations were higher in
green beans than in the leaf and were lowest in the soil. In most cases, the
concentrations of microelements found in the soil determined the levels in the
leaf and in the green bean. Microelement availability and concentrations were
influenced by the interaction between the various elements, tree age,
elevation, soil texture and location.
Conclusions:
Mineral element K and microelement Cu were found in their highest concentration
in the green bean. Mn, Zn and B were important elements in the determination of
organoleptic cup attributes whereas soil, leaf and green bean nutrient
concentrations were important in determining the medium size of the bean. EDXRF
is an effective tool in the measurement of micronutrient concentrations of
Robusta coffee growing soils, leaves and green beans. Cu was an essential
microelement of physiological and metabolic processes in both leaves and in the
green bean whereas Mn, Zn and Fe are critical microelements during
photosynthesis. While all the trace elements measured, namely, Mn, Cu, Fe and
Zn were crucial determining factors in bean and cup qualities of Robusta
coffee, Zn and Mn were the more important microelements during fruit development.
Soil Mn positively influenced flavor and aroma cup attributes whereas green
bean amounts of B and Zn positively influenced trigonelline and caffeine
concentrations.
Author(s) Details
Prof. Kahiu Ngugi
Department of Plant Science
and Crop Protection, Faculty of Agriculture, College of Agriculture and
Veterinary Sciences, University of Nairobi, P.O.BOX 29053-00625, Kangemi,
Nairobi, Kenya.
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