Evaluation of Inorganic and Organic Fertilizers on Productivity and Quality of Bixa Orellana in Kwale County, Kenya
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Date
2024-05
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Kenyatta University
Abstract
Bixa (Bixa orellana) is a small evergreen shrub that grows to a maximum height of 20–33
feet (6–10 m). It can grow in a wide variety of tropical to subtropical climates with very
little care and low rainfall levels. However, it is faced with a number of challenges:
competition with cheap synthetic food colours; low production and productivity; low
quality of bixa in terms of bixin levels (less than 2.5% as opposed to 3.5-4.0%). This study
was aimed at evaluating the effect of inorganic and organic fertilizers on productivity and
quality of bixa orellana in Kwale County of coastal Kenya. A baseline survey was
conducted in the major bixa producing areas of Kwale County to determine the status of
bixa farming where a structured questionnaire was administered to 300 respondents. Bixa
seeds and soils were sampled from farms in each of the sub-counties and subjected to seed
quality tests and soil nutrient level analysis respectively. Evaluation trials on the effect of
inorganic and organic fertilizers on productivity and quality of Bixa were also conducted
through a field trial that was established in an existing bixa plantation at the Kenya Bixa
Company Nucleus Farm in Shimoni area of Kwale County. Bixa plants of the red pointed
variety, pink rounded and green pointed variety with the same age (5 years old) were
subjected to treatments of different levels of organic and inorganic fertilizers in a factorial
experimental unit arranged in a randomized complete block design (RCBD) replicated
three times. The treatments comprised of two levels of NPK fertilizer (100kgs/ha,
150kgs/ha) and 2 levels of poultry manure (5 tons/ha, 10 tons/ha) as well as a combination
of the two at half rates (2.5 tons/ha manure +50 kgs/ha NPK and 5 tons/ha manure +75
kgs/ha NPK) together with a control. Post-harvest handling studies on bixa were also
conducted. Data from the experiments was analyzed using R software. A p-value of less
than 0.05 was considered significantly different. The results indicated that Bixa farming is
a major income generating enterprise for the smallholder farmers in Kwale County. The
prices for bixa at the farm gate have been increasing on annual basis as a result of the
increased demand for natural food colours in the world markets. The treatments of NPK
fertilizers at the rates of 100 kg/ha and 150kg/ha respectively as well as that of manure at
the rate of 10t/ha recorded the highest yields and bixin levels in all the three blocks. The
drying method that produced the best results in terms of the bixin quality was that of
drying at 50% shade conditions. The optimum nutrient levels were realized in the
treatment manure at rate of 10t/ha and that of NPK applied at the rates of 100kg/ha and
150kg/ha respectively. On distribution of nutrients in the bixa plant, a majority of the
nutrients were found in the leaves followed by roots and then stems respectively. Both the
Rhizosphere soil pH and electrical conductivity (EC), improved with the application of
organic fertilizer soil amendments, while the EC significantly reduced with increased use
of organic fertilizer amendments. In conclusion, the study revealed that the use of organic
and inorganic fertilizers can increase yields and bixin levels in bixa. This was also true for
the levels of nutrients in the soil as well as the rhizosphere soil pH and soil EC. The study
recommends that farmers be sensitized on the importance of soil testing and use of
manures to improve soil fertility and yields of quality bixa for increased household
incomes. They also need sensitization on proper post-harvest handling procedures for bixa
from the time of harvesting to drying and storage. The Kenya Bixa Company should
consider motivating farmers by paying them for their produce in terms of the bixin content.
Description
A Thesis Submitted in Fulfillment of the Requirements for the Award of the Doctor of Philosophy in Agronomy in the School of Agriculture and Environmental Sciences of Kenyatta University, May 2024.
Supervisors
1. Joseph Onyango Gweyi
2. Jane Ambuko
3. Lusike A. Wasilwa