Determination of Soil Fertility Index Parameters and Speciation of Potassium and Molybdenum in Soils from Selected Farms in Kakamega County, Kenya
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Date
2021
Authors
Lumula, Godfrey Alielo
Journal Title
Journal ISSN
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Publisher
Kenyatta University
Abstract
Kakamega-County is a maize growing region with a high potential of being one of
Kenya‟s maize baskets even though most farmers practice subsistence maize farming.
However, available data show that yields have been dropping with each passing year in
spite of continued application of nitrogenous fertilizers such as calcium ammonium
nitrate (C.A.N) and diammonium phosphate (D.A.P). To get some insight into the
possible causes of decline in maize yields in the region, it was important to conduct a
systematic study to determine the fertility index parameters of the soils in the farms and
speciation of some of the important elements required for plant growth and utilization
of applied nitrogenous fertilizers by plants. The objective of this study was to determine
the soil fertility index parameters (i.e. organic carbon, soil pH, phosphorus, total and
available nitrogen) as well as the speciation of potassium and molybdenum in soils from
five selected farms in Kakamega County. The study was conducted in five different
maize growing farms selected randomly from five sub-counties. On each farm, soil
samples were scooped from five different sampling locations in a zigzag pattern using
an auger at a depth of 0 to 20 cm and mixed thoroughly to form the composite sample.
Accurately weighed portions of each of the composite samples (usually ½ kg) were
packed in clean polythene bags, labeled and transported to Kenyatta University for
laboratory analysis. Modified Community Bureau for Reference (BCR) sequential
extraction was used to obtain extractions of potassium and molybdenum in various soil
fractions. The concentrations of the metals in the fractions were determined using AAS.
All measurements were done in triplicate and results presented as means with standard
deviations. The results revealed that the soils had a low pH ranging between 4.72±0.01
and 5.53±0.01. Soil Organic Matter ranged between 2.21±0.01 and 3.10±0.00% (critical
level is 3.44%), nitrogen ranged between 0.12±0.00 and 0.17±0.01percentage (critical
level is 0.2%), exchangeable potassium ranged between 0.50±0.01 and 1.50±0.01
mg/kg (critical level is 6.0 to 8.0mg/kg). Available potassium ranged between
0.30±0.01 and 1.10±0.01 mg/kg (critical level is 2.4 mg/kg). Molybdenum was below
detectable levels in the bulk soil of four out of five farms. BCR results still showed
molybdenum below detectable levels in all the four soil fractions of farms I, II, III and
IV, (critical level is 0.043 mg/kg). The level of potassium was found to be between
5.09±0.88 and 6.85±2.00 mg/kg in the residual form. Four of the farms were found to
have a low pH value of below 5.0 (critical level is 5.5). Potassium and molybdenum
were not in bioavailable forms. Other nutrients found to be below critical levels were
zinc, phosphorus and magnesium. It is recommended that farmers in the county lime the
soils appropriately to correct pH and use fertilizers rich in micronutrients such as zinc
and magnesium. They are also advised to practice organic farming, use potash as well
as apply dolomite lime.
Description
A Thesis Submitted in Partial Fulfillment of the Requirements for the Award of the Degree of Master of Science (Chemistry) in the School of Pure and Applied Sciences of Kenyatta University, June, 2021
Keywords
Determination, Soil Fertility Index Parameters, Speciation of Potassium, Molybdenum, Soils, Selected Farms, Kakamega County, Kenya