PHD-Department of Agricultural Sciences and Technology

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Assessing Nitrogen Flows and Greenhouse Gas Emissions in Low Input Cropping Systems of Lake Victoria Basin
(Kenyatta University, 2022) Ntinyari, Winnie; Joseph Onyango Gweyi; Cargele Masso; Benson Mochoge
Too little nitrogen (N) is a threat to cropping systems and soil fertility in sub-Saharan Africa (SSA). Nitrogen budgets (NB) and nitrogen use efficiency (NUE) are critical tools for assessing N dynamics in agriculture and have received little or no attention in the region. The study aimed to assess key N performance indicators at field and farm level based on N use scenarios and helps to inform policy on formulating relevant decision and practices to enhance N management for improved crop productivity and environmental sustainability. To achieve this, data were collected from farmers’ fields and clustered into two categories, farmers applying and farmers not applying N fertilizers. Collected data on yield and N fertilizer were used to make projections on the changes of NUE based on scientific and policy recommendations for Sub-Saharan Africa for 2020 (base year), 2025, 2030, and 2050. Scenarios of N use were simulated under field conditions for maize crop in two catchments of the Lake Victoria basin. The scenarios included Business as Usual (BAU, 0 kg N ha-1), 25 % of the Abuja declaration (ADS 12.5 kg N ha-1), 50% of the Abuja declaration (ADS 25 kg N ha-1), and Abuja declaration-Abuja scenario (ADS, 50 kg N ha-1). A laboratory incubation experiment to assess the effects of two N use scenarios (12.5 and 50 kg N ha-1) and liming practices (CaCO3) on three acidic soils types from Lake Victoria basin on greenhouses gases was conducted. Data were analyzed using R programming language version 4.1.0. The results revealed negative N balances in different fields and farms. Similarly, at the farm gate, a deficit of -78.37 kg N ha -1 was observed; an indicator of soil N mining. Significant differences in maize grain yield for both fertilized and unfertilized farms were realized with very low yields of 2.4 t ha-1 (fertilized) and 1.4 tha-1 (unfertilized). The graphical representation of NUE of both maize and rice showed that most farmers were in the zone of soil N mining. Projected results showed that most maize farmers within Lake Victoria region will continue to experience NUE values >90%, low N inputs <50 kg N ha-1) and less than 5 t ha-1 maize crop yield over the years. For rice farmers, Nyando and Nzoia catchments had surpassed the set target of both yield (6 t ha-1) and N input (50 kg N ha-1). The results revealed that increasing N input levels significantly influenced the growth and yield of maize crops. N deficits were observed in all the N use scenarios with a range of -66.6 to -125.7 kg N ha-1 in Nyando and -62.5 to -105.4 kg N ha-1 in Rangwe catchments with 50 % ADS scenario having the highest deficits. The partial N balance observed at Nyando (1.56 - 3.11) and Rangwe (1.10- 4.64) were higher than the optimal values, a sign of insufficient N inputs and possible risk of soil N depletion in all the scenarios. The values of δ13C of CO2 showed that the source of CO2 from soils was negligible and the largest contributor was from application of CaCO3 followed by N fertilization in Ferralsol 1 and 2 while no visible differences observed in the Vertisol. N2O-N fluxes were highly influenced by N fertilization and CaCO3 in Ferralsol 1 and 2 which was 13 (81.73 mg m-2) and 4 (38.80 mg m-2) times higher when compared to unfertilized and unlimed control. The study concludes that Lake Victoria basin faces an extreme depletion of available N resources, the recommended nutrient level; at 50 kg N ha-1 is not sufficient to correct the negative balances, while managing acidity and soil fertility will lead to higher GHG fluxes but increase N availability.
Assessing nitrogen flows and greenhouse gas emissions in low input cropping systems of lake Victoria basin
(Kenyatta university, 2022-12) Ntinyari, Winnie; Joseph Onyango Gweyi; Cargele Masso; Benson Mochoge
Too little nitrogen (N) is a threat to cropping systems and soil fertility in sub-Saharan Africa (SSA). Nitrogen budgets (NB) and nitrogen use efficiency (NUE) are critical tools for assessing N dynamics in agriculture and have received little or no attention in the region. The study aimed to assess key N performance indicators at field and farm level based on N use scenarios and helps to inform policy on formulating relevant decision and practices to enhance N management for improved crop productivity and environmental sustainability. To achieve this, data were collected from farmers’ fields and clustered into two categories, farmers applying and farmers not applying N fertilizers. Collected data on yield and N fertilizer were used to make projections on the changes of NUE based on scientific and policy recommendations for Sub-Saharan Africa for 2020 (base year), 2025, 2030, and 2050. Scenarios of N use were simulated under field conditions for maize crop in two catchments of the Lake Victoria basin. The scenarios included Business as Usual (BAU, 0 kg N ha-1), 25 % of the Abuja declaration (ADS 12.5 kg N ha-1), 50% of the Abuja declaration (ADS 25 kg N ha-1), and Abuja declaration-Abuja scenario (ADS, 50 kg N ha-1). A laboratory incubation experiment to assess the effects of two N use scenarios (12.5 and 50 kg N ha-1) and liming practices (CaCO3) on three acidic soils types from Lake Victoria basin on greenhouses gases was conducted. Data were analyzed using R programming language version 4.1.0. The results revealed negative N balances in different fields and farms. Similarly, at the farm gate, a deficit of -78.37 kg N ha -1 was observed; an indicator of soil N mining. Significant differences in maize grain yield for both fertilized and unfertilized farms were realized with very low yields of 2.4 t ha-1 (fertilized) and 1.4 tha-1 (unfertilized). The graphical representation of NUE of both maize and rice showed that most farmers were in the zone of soil N mining. Projected results showed that most maize farmers within Lake Victoria region will continue to experience NUE values >90%, low N inputs <50 kg N ha-1) and less than 5 t ha-1 maize crop yield over the years. For rice farmers, Nyando and Nzoia catchments had surpassed the set target of both yield (6 t ha-1) and N input (50 kg N ha-1). The results revealed that increasing N input levels significantly influenced the growth and yield of maize crops. N deficits were observed in all the N use scenarios with a range of -66.6 to -125.7 kg N ha-1 in Nyando and -62.5 to -105.4 kg N ha-1 in Rangwe catchments with 50 % ADS scenario having the highest deficits. The partial N balance observed at Nyando (1.56 - 3.11) and Rangwe (1.10- 4.64) were higher than the optimal values, a sign of insufficient N inputs and possible risk of soil N depletion in all the scenarios. The values of δ13C of CO2 showed that the source of CO2 from soils was negligible and the largest contributor was from application of CaCO3 followed by N fertilization in Ferralsol 1 and 2 while no visible differences observed in the Vertisol. N2O-N fluxes were highly influenced by N fertilization and CaCO3 in Ferralsol 1 and 2 which was 13 (81.73 mg m-2) and 4 (38.80 mg m-2) times higher when compared to unfertilized and unlimed control. The study concludes that Lake Victoria basin faces an extreme depletion of available N resources, the recommended nutrient level; at 50 kg N ha-1 is not sufficient to correct the negative balances, while managing acidity and soil fertility will lead to higher GHG fluxes but increase N availability.
Characterization, Water Stress and Nutrient Management of Yellow Passion Fruits (Passiflora Edulis, Var F. Flavicarpa. Deg) in Kiambu and Embu Counties, Kenya
(Kenyatta University, 2019-06) Mwirigi, Peter
Passion fruit has gained significant importance as a horticultural crop of choice among farmers in Kenya. The yellow passion has been recently commercialized in Embu County due to its adaptation to the hot arid conditions and potential for high yields. Currently, the production levels of the fruit are low due to poor agronomic practices, declining soil fertility levels and changing climate leading to reduced rainfall. To further understand these challenges, there is need for careful investigation of plant-soil-water relations which requires careful in-depth analysis of the soil’s nutrients of any area. This is because each nutrient has a specific role to play in the development of the plant and deficiency symptoms will manifest specific to each nutrient. Further, to establish and manage nutritional and water stress related disorders, their causes requires knowledge of the symptoms. The primary objective of this study was to carry out socioeconomic survey of passion fruit farmers and determine the correct water and nutrient management of yellow passion fruit in Embu County. The study also carried out morphological characterization of the cultivated populations to identify hybrids with favorable characteristics such as drought tolerance. The study involved a mixture of field survey, on-farm experiments with selected farmers and controlled experiments at Kenyatta University research farm. Results of the survey established that majority of the farmers grow passion on small acreages of less than 2 acres and have a common source of planting materials. Further, major agronomic practices including fertilizer and water application were also not correctly followed. The results on morphological characterization indicate the presence of two main groups of cultivars. Further, for fertilizer application, the study established that the treatments 100g DAP+20kg Manure+50g CAN and 20kgManure+50gNitrabor had the best impact on flowering (p≤0.05) and fruit development while results on determination of water uptake established the treatment of 10 liters of water per day giving the longest primary vine and highest number of secondary vines (p≤0.05). In conclusion, field survey and on-farm experimental results indicate the need for increased availing of new knowledge to farmers in the management of the crop while results from controlled experiments at the university farm indicate a need for correct application of fertilizers and efficient monitoring of irrigation regimes. All these factors will lead to improved quality and quantity in yield of yellow passion fruit. The study recommends provision of updated agronomic management practices to yellow passion farmers in Embu County, the use of either 100gDAP+10kgManure+50gNitrabor, 100gDAP+20kgManure+50gNitrabor or 50gDAP+10kgManure+50gNitrabor and the application of 10 liters of water per day per plant for optimum yield of passion fruits. Future studies on nutrient partitioning and water use efficiency can also be conducted to have a clear understanding of the nutrient and water relations in yellow passion fruit.
Combined Effects of Tillage, Mulching and Nitrogen Fertilizer Application on Maize Yields and Soil Properties in Tharaka-Nithi County, Kenya
(Kenyatta University, 2018-09) Abdi, Zeila Dubow
High dependence on rain-fed agriculture, low and erratic rainfall, inadequate water and soil conservation techniques and declining soil fertility expose resource-poor farmers to low agricultural productivity in tropical regions. A study was conducted in 2012 at Kirege Primary School in Tharaka Nithi County to evaluate the effects of soil tillage, soil surface management and nitrogen fertilisation on rain-fed maize yields and properties of Humic Nitisols. Eight treatment combinations (T1M0N1, T1M0N0, T1M1N1, T1M1N0, T0M0N1, T0M0N0, T0M1N1 and T0M1N0) were laid out in randomised complete block design and replicated thrice. Data on grain and stover yields, mineral N, soil water content and soil organic carbon content were collected over six cropping seasons. Physical fractions of soil organic matter were evaluated down to 0-80 cm depths. T1M1N1 and T1M0N1 treatment combinations significantly had the highest maize yields in three out of six seasons (SR2013, LR2014 and SR2014), ranging from a low of 1.9 Mg ha-1 in SR2013 to a high of 4.9 Mg ha-1 in LR2015. T1M1N1 combination was superior for stover yields in four out of six seasons, ranging from a low of 2.7 Mg ha-1 in SR2013 to a high of 7.9 Mg ha-1 in LR2015. T0M0N1 combination had highest water use efficiency for biomass production (WUEB), with the highest water use efficiencies noted in LR2014 at 13.3 kg ha-1 mm-1 and short rains 2014 at 9.6 kg ha-1 mm-1 .Significantly higher WUEGY of 9.6 kg ha-1 mm-1 were recorded in T0M0N1 in short rains 2014 and 3.4 kg ha-1 mm-1 in T1M0N1 in long rains 2015. Generally, the NO3-N concentrations in all treatments decreased with increase in soil depth from 0-20 and 20-40, after which the concentrations increased from 40-60 and 60- 80 cm depths. There were significant differences in the amount and distribution of soil nitrate-N at the depths of 60-80 cm at 10 WAP, with higher net N mineralisation in minimum tillage treatments than in conventional tillage treatments. The highest soil water content in the study conserved in the minimum tillage with mulch retained at 0 kg of N fertiliser while minimum tillage treatments had higher crop evapotranspiration. Overall, soil carbon content decreased with increase in soil depth. In all the three class size aggregates, the highest increases in soil carbon were noted in the 0-20 cm depths, with the highest overall increases in both soil meso-aggregates and macro-aggregates between 2012 and 2015 observed in T1M1N1 combination. There was enhanced soil carbon in the 0-20 cm depth in all the three aggregate fractions in treatments with conventional tillage combinations, with increases of 3.5 t C ha-1 in micro-aggregates, 2.2 t C ha-1 in meso-aggregates and 3.7 t C ha-1 in macro-aggregates. While more rains fall during the SR seasons, the LR seasons were found to be more important, with higher grain and stover yields in SR than LR. Retention of mulch on-farm was found to be crucial for soil water conservation at soil depths below 50 cm and enhancing mineralisation of nitrogen, showing a clear potential for seasonal water buffering. This underscores the possibility of adapting to erratic climate regimes. This research has confirmed the importance of conventional tillage practices in ensuring better maize yields for farmers and promoting soil C content in smallholder maize-based farming systems conducted in Humic Nitisols and that in the long-term the formation of stable micro-aggregates in smallholder farms can be useful carbon sinks.
Efficiency and Competitiveness of Chicken Production in Machakos, Kiambu and Uasin Gishu Counties, Kenya
(Kenyatta University, 2023) Samba, Scolastica Mwikali; Ibrahim Macharia; Gabriel Mwenjeri
A company's or industry's competitiveness is its capacity to successfully compete in order to achieve sustainable growth and earn at least the opportunity cost of the resources used. The poultry sector is very important to the economy of Kenya and plays a key role in food and income security of majority of the producers who are mostly in rural areas. There has been high imports of poultry products from Uganda and China to the country in the past five years causing an uproar by local producers who complain of cheap products flooding the market and affecting their profits. In 2020, Kenya imported 1,000 MT of eggs with zero exports despite having a surplus in egg production. This study was therefore to assess the competitiveness and efficiency of chicken production in Kenya to determine the level of efficiency and ability to produce quality products at relatively lower costs. The specific objectives were; determine the technical, cost and allocative efficiency levels, assess the factors influencing these levels and investigate the competitiveness of improved indigenous chicken farmers in Kenya. Data were collected from 384 small-scale chicken producers across three counties of Kenya (Uasin Gishu, Machakos and Kiambu). A semi-structured questionnaire which had been uploaded on android phones was used to obtain data .A stochastic frontier analysis was carried out to determine the technical and cost efficiency of improved chicken producers in the three counties and factors influencing the efficiencies and a policy analysis matrix approach (PAM) was used to measure the competitiveness of the producers. Results indicated that majority of the farmers were middle aged women who had formal education. The major constraint of chicken production was cost of feeds which had driven some producers of the chicken enterprise. Results indicated that the producers attained an average technical efficiency of 58%,cost efficiency of 39% and allocative was 67%, which were low compared to efficiency scores recorded elsewhere. Some of the socio and institutional factors affecting the efficiencies included; household size, education level of household head, access to extension services, distance to input and output markets and distance to a tarmacked road. Results from the PAM indicated that they were competitive at social values but uncompetitive at private values. The study recommends that research institutions develop cheaper alternative sources of starch and proteins to cut down cost of feeds. It is also recommended that extension services are enhanced to improve farmers’ knowhow on feed formulation, housing and disease management.
Evaluation of Inorganic and Organic Fertilizers on Productivity and Quality of Bixa Orellana in Kwale County, Kenya
(Kenyatta University, 2024-05) Finyange, Pole
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.
Fingerprinting and Relating Juvenile Characters of Rice to Yield and Yield Components in Kiambu and Kirinyaga Counties
(Kenyatta University, 2019-02) Henga, Sylvia A.
Rice is increasing as an important food and cash crop in Kenya and is third to maize and wheat in terms of consumption. Consumption has continually outstripped production resulting in massive importation. The main problem affecting productivity involves lack of proper information on best storage time, use of poor quality seed, varietal admixtures which has contributed to low yields. There is need to characterize genotypes. Microsatellit are useful in various plant genetic studies and plant characrerization. Accelerated aging is considered an excellent option as a vigor test due to shortest time of acquisition and efficient results. In the proposed study, seed quality experiments including germination, dormancy, purity, were carried out in the laboratory using eight rice varieties in a Completely Randomized Design. Accelerated ageing tests at 0,24,48 and 72hrs(45oC and 98%RH) were carried out JKUAT post-harvest laboratory using eight rice varieties‟ in four replications of100 seeds each. Data was collected on dates to plumule and radical emergence and height. Five varieties were used to produce seeds which were stored for 1,2,3,4,5 and 6 months respectively. The seedlings were transplanted into fields in a Randomized Complete Block Design using 5*6 factorial arrangement. The study also determined the relationship between juvenile characters and adult characters of rice in Kiambu and Kirinyaga counties. All the data were analyzed using GENSTAT statistical package. ANOVA and LSD at 5% significant level. Seed quality results showed that There was significant variation in both coleorrhiza and coleoptile formation among rice varieties (p<0.001), treatments (p<0.001) and interaction between rice varieties and treatment ((p<0.001). The difference between all treatments was significant with 72 hours treatment having the highest number of days to coleorhiza and coleoptile formation. Results showed that the effect of genotype on coleorhiza and colleoptille formation was significant (p<0.001). Genotype B317 had the earliest colleoptile formation 8.75days, coleorhiza formation (9.81), B317 also had the highest germination percentages at 7(33.69), 14 (52.44) and at 21 days after sowing (56.62). Mzungu had the latest number of days to coleorhizae (12.44), coleoptiles (11.18) and lowest germination percentages at 14(27.52) and 21days (31.31). The genotype had significant effect on germination index, seed length and seedling vigor index. In Mwea, there was a significant effect of storage time on germination, with 4 months giving the highest seedling vigor index (673.6), height at 1 month after transplanting (73.3cm), height at maturity (72.3cm) and 3 months giving the highest days to flowering(58.87) .The interaction between storage time and genotype on was significant, with genotype B217 stored for 3 months leading in height at one month after transplanting (87.7), height at maturity(91.8cm) .in Kiambu.The interaction between storage time and genotype was significant with 5months of storage having the highest seedling vigor index (759.5), 1000grain weight (69) and yield (15.5kg/ha). Analysis of molecular variance results indicated that the five polymorphic markers used in this study showed a total of 11 alleles across the loci of the 18 rice genotypes studied. Juvenile characters such as seedling vigor and height at transplanting had a positive and significant correlation to 1000grain weight.Genotypes TXD and B217 were identified by the 5 markers. TXD (Saro 5) was the best fit for fingerprinting as it was identified by only 1 marker. These results could be used in preparing rice seed certification procedures, in gene bank management and other seed storage ventures
Identification and characterization of Sorghum (sorghum bicolor (l.) Moench) landraces and improvement of on-farm seed production in Eastern Kenya
(2014-08-19) Muui, Catherine W.
Sorghum (Sorghum bicolor (L.) Moench) is an under-utilized crop that is tolerant to drought, flooding, saline-alkaline, infertile soils and high temperature. Farmers maintain landraces through preference selection and obtain seed from different sources. Local germplasm provides greater genetic variability and may provide useful traits to broaden the genetic base. Decline in use may erode the genetic base, preventing use of distinctive traits in crop adaptation and improvement which may result in their disappearance. There is also lack of information on on-farm seed production strategies leading to lack of quality seeds, information on use and improved cultural management. The objectives of this research were to identify and determine the key sorghum landraces grown in lower eastern Kenya, establish their diversity, quality levels for seed used by farmers, come up with pre and post harvest handling methods that could be used by farmers to improve on-farm seed quality. A baseline survey was conducted and landraces collected in various agro-ecological zones of lower eastern Kenya. Morphological and molecular characterization, varietal assessment in different ecozones and seed quality tests were done. Two varieties were used to test the effect of location of seed on different panicle sections, storage containers, and seed drying at different times of the day for different duration on seed quality. Results showed that farmers maintain a diversity of landraces unique in adaptation, food quality, grain yield, quality of harvested products and biotic stress resistance. They obtain seed for planting from informal systems of which 36% recorded low viability and 38% low vigor with 85% of seed samples contaminated with either Fusarium sp., Penicillium sp., Rhizorpus sp., Aspergillus niger and Aspergillus flavurs. The landraces recorded low heterozygosity indicating high level of stability in the population. Landraces clustering based on geographical locations was distinct with some overlaps across the locations. Variations were observed for leaf and mid rib colour, panicle compactness, awns and seed colour. A wide range of quantitative characters was observed between the accessions. The lower third part of the panicle recorded the highest seed viability and vigor indicating deterioration had not occurred compared to other panicle parts. The highest seed viability and vigor was realized in seed stored in the gourds and the seed stored for four weeks. Significant differences (P=0.05) were observed in leaf area, leaf, shoot and root length, and in dry matter accumulation among the seeds sampled after one month, two months and three months after storage. The seed viability and vigor decreased with increase in time the seed was sun dried but had no negative effect on seed dried in the seed drier. Farmers maintain a diversity of landraces, and since the region has a high agricultural potential, productivity for better food security could be improved by use of locally available germplasm adapted to this particular environment. Sorghum production may be effectively increased by use of improved production technologies and teaching farmers the importance of the crop to increase the production area. Seeds used by farmers to plant their crop are of poor quality in relation to germination, vigor and pathogen infestations
Identification of Stem End Rot Fungal Pathogens on Avocado Fruits and Efficiency of Fungicides and Trichoderma spp. in Murang’a County, kenya
(Kenyatta University, 2021) Wanjiku, Mwaura Elizabeth; Waceke Wanjohi; Jeska Mbaka
Avocado (Persea americana Mill.) is a commercially important fruit cultivated in tropical and sub-tropical climates. In Kenya the fruit is cultivated for both local and export market, significantly contributing to the country’s GDP. The production of avocado fruits in Kenya is limited by fruit diseases among others. Stem end rot (SER) is an economically important post-harvest disease of avocado fruits contributing to losses of the fruits at the farm level, during storage and on the shelves. The causal agents of the disease in Kenya are not clear, but Botryosphaeriaceae spp. are most important causal agents of avocado SER in other parts of the world where the fruit is grown. This study was conducted to evaluate avocado production and SER disease management; determine the incidence of SER on avocado fruits in Murang’a County; identify the SER fungal pathogens, determine the efficacy of selected fungicides and the inhibitory effect of selected Trichoderma species against the SER fungal pathogens of avocado fruits. A structured questionnaire was administered by face-to-face interview with farmers while colony growth and conidia characteristics were used in morphological identification of the pathogens. Two fungicides, (Green Cop 500WP (Copper oxychloride 500g/Kg) and Milraz 76 WP (Propineb 70% + Cymoxanil 6%) were used in the in vitro inhibitory study while four Trichoderma spp. (T. asperellum, T. harzianum, T. atroviride and T. virens) were tested against the most isolated SER pathogens on post-harvest ‘Hass’ avocado fruits. The survey revealed that 84% of the farmers preferred ‘Hass’ avocado fruits, 85% intercropped the avocado fruits with food crops, while 88% of the farmers used organic manure only to replenish the soils. Majority of the farmers (62%) used grafted seedlings while 27% of the farmers top worked the old trees. Most farmers (84.6%) did not adopt the recommended field management practices, and none of the farmers used fungicide in the management of SER. Avocado fruits from the market and orchard had SER disease incidence of 52.08 % and 45.70 % respectively. Lasiodiplodia theobromae, Neofusicoccum parvum, Nectria pseudotrichia, Fusarium solani, Fusarium oxysporum, Fusarium equiseti and Geotrichum candidum were identified as the causal agents of SER on avocado fruits. Lasiodiplodia theobromae was the most frequently isolated pathogen followed by, N. parvum, N. pseudotrichia and F. solani respectively. All the fungicides significantly (P≤0.05) inhibited mycelial growth of the four pathogens. In both in vitro study and on post-harvest avocado fruits T. atroviride had highest efficacy against N. parvum, N. pseudotrichia and F. solani while T. harzianum had the highest efficacy against L. theobromae. This study has identified the causal agents of stem end rot disease of avocado fruits in Kenya. Trichoderma atroviride and T. harzianum present a potential alternative to synthetic fungicides against SER diseases of avocado fruits, and the possibility of using them at a commercial level should be explored.
Improving Soil Properties and Growth of Casuarina Equisetifolia through Use of Biochar, Manure and Inorganic Fertilizer in Kilifi County, Kenya
(Kenyatta University, 2023) Mwadalu, Riziki Umazi; Benson E. Mochoge; Benjamin O. Odanga
Soil fertility challenges coupled with frequent droughts in arid and semi-arid lands (ASALs) have led to massive crop failures thereby increasing the problem of food insecurity. As climate change unfolds, there is a need for technologies that boost soil moisture while enhancing soil fertility. Biochar has been reported to be an effective soil amendment with the capability of enhancing soil productivity. However, the impact of biochar on tree growth is still outstanding. Therefore, the present study aimed at evaluating the potential of biochar, manure, and NPK to enhance Casuarina equisetifolia (Casuarina) growth at different growth stages through nursery and field experiments using randomized complete block experimental design. The nursery experiment evaluated the effects of 0% biochar (control), 10% biochar, 20% biochar, 10% manure, 10% biochar + 10% manure, and 20% biochar + 10% manure on Casuarina growth at the seedling stage. The field experiment evaluated the effects of four biochar rates (0, 2.5, 5.0, and 7.5 t ha-1), 5 t ha-1manure, 50 kg ha-1 of NPK, and a combination of the different biochar rates with manure and NPK on Casuarina growth and soil physical-biochemical properties. All treatments were replicated thrice. At the seedling stage, seedlings treated with 10% manure significantly enhanced Casuarina height by up to 46.8% and collar diameter by up to 30.7% compared to the control (p<0.05). For the field experiment, 7.5 t ha-1 biochar treatment yielded a higher Casuarina height of < 23.4% than the unamended treatment. The lowest biochar rate of 2.5 t ha-1 yielded a higher collar diameter of < 30.2% in comparison with the unamended treatment. Largely, soil bulk density decreased with biochar application by <23.2% compared to the unamended treatment after utilization of the highest biochar rate. The use of 7.5 t ha-1 biochar yielded the highest soil moisture content, which increased by up to 108% compared to the untreated control across the assessment periods. In terms of biochar’s impact on soil chemical properties, there was substantial soil pH improvement of up to 21.3% after biochar application of 7.5 t ha-1; there was an increase of up to 1.3 pH units. Total nitrogen increased by 32.4% after biochar addition while total carbon increased by four-fold. Available phosphorus and Cation exchange capacity (CEC) increased by up to 263.7% and up to 95.2%, respectively, following biochar application. Soil bacteria increase by up to 32.6% and fungi by up to 47.6% after biochar utilization in comparison with the unamended treatment. Ameliorating soil with 7.5 t ha-1 biochar yielded higher Casuarina height than the sole application of NPK. These results strongly suggest optimal growth of Casuarina seedlings requires the application of manure with high nutrient contents at the seedling stage while the application of biochar at field establishment has the potential to enhance the growth of Casuarina and improve soil physical-biochemical properties.
Integration of Thymol, Soil Improvers and Biostimulants for Management of Tomato Pests, Diseases, Nematodes and Rhizosphere Microbial Dynamics Kirinyaga County, Kenya
(Kenyatta University, 2022) Wafula, Geoffrey Ongoya; Waceke Wanjohi; Joseph Gweyi; Joseph Gweyi
Soil-borne pathogens, root knot nematodes and insect pests remain a major constraint to tomato Solanum lycopersicum L. (Solanales; Solanaceae) production in Kenya. The study was carried out with an aim of evaluating the effect of integrating selected plant essential oils, soil improvers and bio-stimulants on rhizosphere microbial, soil-borne pathogens, nematodes and insect pests of tomato. The plant essential oil used (treatments) in this study were thyme oil, bio-stimulants (Trichoderma harzianum), sea weed (Ascophyllum nodosum and Fucus vesiculosus), a sea weed with humic acids, a sea weed with amino acids, peptides and an amino acid; while the soil improver was based on pellets of plant-based raw materials and seaweeds containing 7.5% N in pure vegetable form, soft ground potassium sulphate with magnesium (4% K2O) and soft ground rock phosphate (2% P2O5). The study was conducted in farmer fields in Kimbimbi and Kagio in Kirinyaga County from September 2016 to July 2017 and in the greenhouse at Kenyatta University from February to October 2018. Data collection was carried out on soil-borne diseases, insect pest population and diversity, plant growth and yield parameters. It was subjected to ANOVA using Genstat statistical packages and means were separated using Fisher’s Least Significant Difference (LSD) at P≤0.05. The results indicated that thyme oil was effective in suppressing the fusarium wilt and early blight by between 49.2% to 65.9% and 58.9% to 84.8%, respectively. Plant essential oils were effective in the management of thrips (mainly Frankliniella occidentalis) and whitefly (Mainly Bemisia tabaci and Trialeurodes vaporariorum) infestations causing a reduction in infestation of between 47% to 68.6 % and 41.3% to 66.2%, respectively. The application of the soil improver had a positive effect on the microbial population of fungi resulting in an increase of active fungi at the soil rhizosphere of tomato plants of up to 292%. Application of T. harzianum was effective in the management of Fusarium wilt (39.6% to 48.6% reduction) and root knot nematodes (48.8% to 60.9% reduction). The integration of thyme oil, soil improver, T. harzianum and bio-stimulants was effective in the management of a reduction of up to 66.9% for Fusarium Wilt, 83.4% for early blight, 60% for root knot nematodes, 66% for thrips and 47.3% for whitefly as well as increasing yield of tomato by up to 125.6%. Based on these results, the integration of thyme oils, Trichoderma harzianum and bio-stimulants can be recommended for management of, fusarium wilt, early blight, root knot nematodes, thrips and whitefly in tomato production.
Molecular characterization and non-chemical management of root-knot nematodes (meloidogyne spp.) on African nightshades in selected parts of Kenya
(Kenyatta University, 2016-04) Nchore, Shem Bonuke
Root-knot nematodes (RKN) (Meloidogyne spp.) cause up to 80 % yield losses in infected vegetables. A study was carried out to; assess the influence of farmers’ knowledge and awareness on RKN damage on African nightshades (AFNS); assess the incidence and severity of RKN on AFNS; characterize the RKN species infecting AFNS; screen the AFNS for response to RKN and determine the efficacy of solarizing soils amended with selected organic materials against RKN. A root-knot nematode survey was carried out in selected farms in Lower midlands 1 (LM1), Upper midlands 1 (UM1), UM2, UM3 and UM4 located in Nandi, Bungoma, Kakamega and Uasin Gishu Counties during the April to July 2014 growing season. The survey revealed that 53.6 % of the AFNS farmers were not aware of RKN. Majority (66.7 %) of the farmers planted AFNS using organic manure while 33.3 % used inorganic fertilizers. Farmers controlled RKN through the use of pesticides, crop rotation, woodash and uprooting diseased crops. Two hundred and fifty soil and root samples were taken from depths of 20 cm from ten different points per farm to determine the disease incidence and severity. Incidence and severity of 94.13 % and 2.63 respectively was reported. Galling index ranging from 1.3 to 4.43 was reported. Molecular characterization identified M. incognita, M. arenaria, M. hapla, M. javanica and M. lopezi from the surveyed areas. The response of AFNS to RKN varied from resistant to susceptible. Solanum eldoretiunum and S. scabrum were resistant, while S. sarrarachoides was tolerant in the greenhouse and field conditions. Solanum americanum and S. nigrum line IP03 were resistant in the greenhouse, but were tolerant to RKN in both field experiments, while S. nigrum landrace from Kakamega and S. opacum were resistant in the greenhouse and field test at Kenyatta University but were tolerant to RKN at Chepterwai. Both S. nigrum from Simlaw Seed Company and S. villosum line BG03 were susceptible in the field test at Chepterwai though they were tolerant in the field test at Kenyatta University. In addition, resistant and tolerant AFNS had lower RKN damage and reproduction compared to susceptible AFNS. Solarized soils amended with Cattle manure (Cm), Tithonia diversifolia (Td) and pymarc (Pm) reduced RKN population and damage significantly compared with non-solarized and non-amended controls. Solarization improved efficacy of Cm, Td and Pm against RKN reproduction and damage on S. villosum. Reproduction was lower on Cm, Pm and Td amended soils while galling index ranged from 0.7 to 2.2 in solarized soils compared to 1.4 – 5.0 in non-solarized soils. Sensitization of farmers on RKN damage and application of organic amendments to reduce disease incidence and severity is proposed. The dominant RKN identified threatens AFNS production in the surveyed regions. Farmers should grow tolerant AFNS on heavily infested soils to reduce RKN population and reproduction. The tolerant AFNS could also be used in breeding programs for the management of RKN. Solarizing soils amended with organic materials is an ideal integrated pest management strategy for combating RKN infecting AFNS.
Performance of Amaranth Accessions against Moisture Stress and Key Insect Pests and Their Indigenous Parasitoids in Arusha, Tanzania
(Kenyatta University, 2019) Othim, Stephen Tarmogin Omburo
Amaranths are African indigenous vegetables (AIVs) that have recently gained importance as a food source in Africa owing to the high nutritional value of their leaves and grains. Production of this crop is, however, limited by arthropod pests especially the lepidopteran leaf-webbers, leaf-worms and stem weevils. The use of insecticides for their management is uneconomical and also present health and environmental concerns. Host plant resistance (HPR) to insects is an effective, economical and environmentally friendly alternative that is poorly understood and unexploited among AIVs. The aim of this study was to assess Amaranthus accessions for resistance to leaf-webbers and stem weevils, their tolerance to water stress conditions and the performance of indigenous parasitoids on selected accessions. Field and laboratory experiments were conducted at the World Vegetable Centre (WorldVeg) in Arusha Tanzania with 36 accessions and lines of amaranth. Accessions VI036227, RVI00027, VI054569, VI033487, VI044432, VI048076, VI049639, VI049530 and VI049698 had high levels of pest resistance with significantly lower infestations (≤ 11.11±2.14%) and damage (≤ 68.06±3.90%) by leaf-webbers and leaf-worms. The accession VI036227 was found to be highly resistant against Spoladea recurvalis, exhibiting exemplary antibiosis by causing 100% larval mortality despite not being deterrent for oviposition. The accessions VI048076, VI056563 and VI047555-B demonstrated moderate resistance against the pest for specific parameters including low oviposition, moderate early stage larval mortality and reduced adult longevity. The relative growth rate (RGR) of accessions VI033479, VI049698 and VI056563 were not significantly affected by the three soil water levels (40%, 60% and 90% water holding capacity (WHC)). Apanteles hemara performed well on all the other moderately resistant accessions except VI056563 that recorded lower parasitism rates compared to the susceptible accession. The longevity of the parasitoid was significantly extended on the resistant accessions compared to the susceptible one. The functional response curve exhibited by A. hemara corresponded to type II functional response with an asymptote at the density of 30 larvae. Apanteles hemara parasitism was significantly higher in 1-2-day-old compared to 3-4-day-old larvae (P=0.04). Thus, accessions VI036227 and VI049698 were identified to be highly resistant to leaf-webbers in addition to 24 moderately resistant ones while VI047517-B, VI036227 and VI056563 had low levels of resistance against stem weevils. Accessions VI033479, VI049698 and VI056563 were also tolerant to moisture stress. The identified pest resistant and water stress-tolerant amaranth accessions from this study are recommended for multiplication and release to farmers to alleviate the effects of pests and drought. These can also be used in breeding programs to improve locally cultivated varieties. The identified parasitoids can also be reared and released into farmer fields to synergize host plant resistance.
Phenotypic Characterization and Evaluating the Response of Sweet potato Genotypes for Drought Tolerance as an Adaptation to Climate Change in Ethiopia
(Kenyatta University, 2023) Gitore, Selamawit Abebe; Benjamin O. Odanga; Sylvia Henga; Fekadu Gurmu
Foremost, I attribute my success to Almighty God, who has granted me the opportunity and equipped me with the necessary knowledge, abilities, and patience. I am also grateful for the support and advice provided by various institutions and individuals that have enabled me to present this thesis in its current form. I extend my heartfelt gratitude to everyone who has stood by me throughout this journey. I express my sincere appreciation to my supervisors, Dr. Benjamin Danga, Dr. Sylvia Henga, and Dr.Fekadu Gurmu, for their guidance and support throughout the research process. Dr.Danga has been with me from the beginning, helping me choose a suitable topic and providing me with office space to write my paper. Dr.Henga has also been instrumental in guiding me with her constructive feedback and preparing me for presentations. Dr.Gurmu has been very helpful, providing me with planting material and monitoring my progress by visiting my work site. I am grateful to my friend, Assistant Professor of Biostatistics at Bahrdar University, Asst. Prof. Kindie Fentahun, for assisting me during the data analysis phase. I would like to acknowledge the European Commission (EU) and the African Union (AU) for funding this research project through the Framework Programme "Intra-Africa Mobility Academic Mobility Scheme," project No 2017-3052/001-001. I am also thankful to the Hawassa Agricultural Research Center for providing me with planting material for this study. Last but not least, I extend my deepest appreciation to my parents for their unwavering support and encouragement throughout my academic journey. Without them, this thesis would not have been possible. I also thank my friends for their daily motivation and encouragement. I hold each and every one of you in high regard.
Population dynamics and management of vectors of viruses causing maize lethal necrosis disease in Bomet County Kenya
(Kenyatta University, 2018-04) Namikoye, Everlyne Samita
Maize production in Kenya is under threat due to infection by maize lethal necrosis disease (MLND). The disease is known to cause intensive complete yield loss. It is caused by a synergistic infection of maize by maize chlorotic mottle virus and sugarcane mosaic virus which are mainly vectored by corn thrips (Frankliniella williamsi, Hood) and corn leaf aphids (Rhopalosiphum maidis, Fitch) respectively. This study was carried out with the aim of investigating the following aspects; farmer‘s knowledge and practices on vectors of MLND causing viruses, movement and dispersal of the two vectors in a maize farm and various management strategies through sticky roll trapping, varietal tolerance, action threshold levels, polycropping systems and biocontrol strategies towards the control of the disease and vectors. Field trials were carried out in Bomet County for two seasons from November 2014 to September 2016 using a randomized complete block design. Data was collected by counting vectors, scoring for MLND severity and disease incidence. Presence of MCMV, SCMV virus was also carried out using ELISA tests. Data was analyzed using Genstat version 17 to get mean and significant means were there after separated using LSD. Survey results indicated majority of respondents in Bomet as being youths aged between 21 to 30 years while 58% of the farmers had attained education up to upper primary level. Only 23% were high school graduates. Majority of the farmers were aware of MLND but only 3% knew about the vectors of MLND.The use of vertically positioned blue sticky traps were more attractive to corn thrips compared to the yellow ones (P = 0.023). Similarly, blue sticky rolls trapped more corn thrips and prevented maize from MCMV infection (P<0.001) while the yellow sticky rolls trapped more corn leaf aphids and prevented maize from SCMV infection (P<0.001). Sampling of maize along the rows gave the best prediction for the vector infestations (P<0.001) while the upper plant region proved most effective for vector sampling.The most appropriate time for vector sampling was from 8.30 am to 10. 30 am as well as from 3.30 pm to 5.30 pm. The monthly spray regime had the highest net returns as compared to all the other spray regimes. More over, maize from the entire thunder sprayed plots tested MLND negative compared to the control that received no spray (P<.001). Results showed variety Pannar as the most resistant to MLND (P<.001) as well as landraces MLR1 and MLR 15 (P = 0.002). The companion crops used in the polycropping system showed coriander harboring significantly more corn leaf aphids compared with other companions (P = 0.04). Furthermore, maize planted with coriander tested negative for SCMV and hence MLND negative. Findings from this study provide scouting and monitoring strategies for both vectors as well as various successful management and control methods for the disease and its vectors. Adoption of techniques such as sampling patterns, sampling time, scouting methods, use of sticky cards and sticky rolls will give an indication of the vector status in the field as well as offer control mitigation measures. Varietal resistance coupled with action thresholds of the vectors and the use of companion crops was able to result into minimal disease spread and reduced chances of MLND occurance. This information can be used to formulate a management strategy for the vectors of MLND causing viruses as well as develop a national vector and disease monitoring plan for both the vectors and the disease. This will culminate into improved maize production and food security.
Production of Organic Fertilizer from Black Soldier Fly Frass for Improved Soil Health and Maize Productivity in Nairobi City County, Kenya
(Kenyatta University, 2021) Dennis, Beesiga Mukama; Benson Mochoge; Nicholas K. Korir
Use of organic wastes for Black soldier fly (BSF) farming presents an avenue that could contribute to improved crop yield and sustainable soil health. A major waste from BSF farming is frass which, however, generates organic fertilizer with low nutrient levels. In addition, and the agronomic performance of BSF frass fertilizer (BSFFF) is not known. This study aimed at producing high quality and cost-effective organic fertilizer from BSF frass for improved soil health and crop productivity. The study evaluated the effects of C:N ratio adjustment (C/N ratios of 11, 15, 20, 25 and 30) and substrate amendment with biochar (0, 5, 10, 15 and 20%) and gypsum (0, 5, 10 and 15%) on nutrient conservation in organic fertilizer. Comparative performance of BSFFF and commercial organic (SAFI) and mineral (urea) fertilizers on maize production was carried out under field conditions. The first experiment involved application of BSFFF and SAFI at sole rates of 0, 2.5, 5 and 7.5 t ha-1., while in the second experiment, BSFFF, SAFI and urea were applied at rates equivalent to 0, 30, 60 and 100 kg nitrogen (N) ha-1. Furthermore, field incubation studies involving BSFFF, and SAFI applied at 5 t ha-1 were also undertaken to determine synchrony of N mineralization for maize production. Finally, data obtained from BSF rearing, frass composting, and agronomic experiments were used to perform economic evaluation. The data obtained were analyzed using R software version 3.6.0. Results indicated that an amended substrate with C:N of 15 increased N and phosphorus (P) retention in frass compost by 21% and 15%, respectively compared to the unamended substrate, and did not cause significant decrease in larval yields. The highest frass compost yield and potassium (K) retention were achieved in amended substrate with a C:N ratio of 20. Amended substrate with biochar and gypsum enhanced N conservation in frass compost, but gypsum was more efficient than biochar. Amendment with 20% biochar significantly increased BSF larval yields (88%) relative to the control substrate while amendment with > 5% gypsum decreased larval yields. The inclusion of 20% biochar generated the highest frass compost yield, gave a 21% increase in N retention and significantly higher K content in frass fertilizer compared to the unamended substrate. Initial composting of organic wastes using BSF larvae significantly shortened compost maturity time to 5 weeks, compared to 8 – 24 weeks in conventional composting methods. Field experiments revealed that plots treated with 7.5 t ha-1 of BSFFF achieved 14% higher maize grain yields than plots treated with a similar rate of SAFI. There was a 27% and 7% increase in grain yields in plots treated with 100 kg N ha-1 of BSFFF compared to those treated with equivalent rates of SAFI and urea, respectively. The agronomic N use efficiency of maize grown using 30 kg N ha-1 of BSFFF was 27% and 116% higher than the values attained using equivalent rates of SAFI and urea, respectively. The BSFFF achieved higher nitrogen fertilizer equivalence values (105 – 229%) than SAFI. Application rates of 2.5 t ha-1 and 30 kg N ha-1 of BSFFF were found to be effective in improving maize yield, while double rates of SAFI would be required. Economic assessment revealed that generating organic fertilizer from BSF frass increased the net income from BSF farming by 5 – 15 times compared to sole larvae production. At equivalent rates, the benefit-cost ratios from maize grown using BSFFF was higher than those of SAFI. Also, the gross margins of maize grown using BSFFF (75 – 78%) were comparable to those of urea (76 – 78%). The findings of this study are crucial in reducing heavy reliance on the costly xvii mineral fertilizers, by adopting high quality organic fertilizers such as BSFFF for improved soil health and productivity.
Pyramiding of Genes Conferring Resistance to Coffee Berry Disease Using Marker Assisted Selection
(Kenyatta University, 2021) Gimase, James Mwita; Wilson M. Thagana; Chrispine O. Omondi
The epidemics of Coffee Berry Disease (CBD), caused by Colletotrichum kahawae, destroy up to 80% of the crop on susceptible varieties if not controlled. CBD control using fungicides increases production cost and environmental pollution, hence the need for resistant varieties. The conventional development of varieties takes 25-30 years, a period that can be reduced using DNA markers. Resistance to CBD is conferred by three genes; R, T and k from varieties Rume Sudan (RS), Hibrido de Timor (HDT) and K7 respectively. The T gene was mapped and adopted in marker-assisted selection (MAS) and there is a need for mapping of the other genes for selection efficiency. The objectives of this study were: to evaluate the suitability of the RSxSL28 F2 genotypes for mapping of a dominant gene, to identify the DNA marker for R gene in RS, to identify genotypes within R11 and Batian with T and R genes using MAS and to pyramid the three genes for CBD resistance in one population. Resistance to CBD of the F2 genotypes from RSxSL28 was evaluated by hypocotyl inoculation test. Genomic DNA was extracted using standard protocols. DNA analysis was carried out using Genotyping by sequencing (GBS) and the filtered sequence reads aligned to the C. canephora reference genome where 1170 Single Nucleotide Polymorphism (SNP) markers were obtained within the 11 coffee chromosomes (Chr). The population structure was determined by Principal Component Analysis (PCA) and marker-based kinship. Genome-Wide Association Study (GWAS) was carried out using the Compressed Mixed Linear Model (CMLM) while QTL analysis was carried out at LOD ≥ 2.5. The DNA markers for R and T genes were used to identify crosses within varieties R11 and Batian with multiple resistance to CBD, which were further utilized to develop a population with the three CBD resistant genes by crossing them to K7. The analysis of variance revealed significant variations among the F2 genotypes and their parents. The PCA and kinship coefficient matrix revealed that 84 F2 genotypes, whose Chi-Square (χ²) test fitted the 3:1 (χ² = 0 and, P≤0.05) Mendelian ratio of segregation for a dominant gene, were ideal for GWAS and QTL mapping. Two SNP markers, 100025973|F|0-59:T>C-59:T>C and 100034991|F|0-44:C>T-44:C>T, were significantly associated with CBD resistance in Chr 1 and 2 respectively, at threshold -log10(P) value > 2.0 on GWAS. The markers were confirmed by QTL mapping, where the first marker was at a distance of 3 centi Morgans (cM) while the second was 12.5 cM from the right and left genes respectively, accounting for 12.5% and 11% of the total phenotypic variation. The marker sequences were associated with proteins for plant defense mechanisms to disease pathogens. Eleven coffee genotypes were confirmed with multiple resistance conferred by T and R-genes. Three out of the eight genotypes were used to develop a pyramiding population with T, R and k genes. In this study, the 84 F2 genotypes are suitable for genetic mapping and are recommended for mapping genes for other diseases, segregating between the two parents. The Two SNP markers associated with CBD resistance in RS are recommended for use in MAS. The 11 crosses confirmed with multiple resistance to CBD are recommended for further distribution to growers since their resistance is broad-based and thus durable while the pyramiding population developed with T, R and k genes is recommended for subsequent selfing to fix the k gene and release as varieties with durable resistance. The study also recommends the mapping of the k gene in K7 for efficiency in selection for multiple resistance to CBD.
Quantifying Greenhouse Gas Emissions and Carbon Stocks in Maize-Soybean Cropping Systems in Siaya County, Kenya
(Kenyatta University, 2020-11) Karanja, Anne Njeri
As climate change continues to threaten ecosystems’ functions, agriculture remains one of the major source of greenhouse gas (GHG) emissions that are responsible for global warming. The major GHG in agriculture are; carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4). Unfortunately, agriculture is also one of the most affected sectors by climate change. There is therefore need to reduce emissions by adopting agricultural practices with mitigation potential. This is by enhancing soil carbon sequestration to offset emissions, or reducing emissions while safeguarding crop yields. However, little is still known about GHG quantities and intensities that major cropping systems in Kenya emmit. Site specific studies on GHG emissions to establish interventions for mitigation of climate change and enhanced crop production is therefore of essence. The objective of this study was to examine the effect of reduced tillage, crop residue retention and use of controlled release urea (CRU) in maize-soybean cropping systems on GHG emissions, soil N mineralization, organic carbon stocks and yields. Field measurements were carried out in a 13 year old researcher-managed trial in Siaya county, Kenya between March 2016 and January 2017. Four treatment combinations: ZT M-S NU (reduced tilage+maize soybean rotation+normal urea), ZT M-S CRU (reduced tillage+maize soybean rotation+controlled release urea), ZT M/S (reduced tillage+maize soybean intercrop without urea), CT M-S NU (Conventional tillage+maize soybean rotation+normal urea) were tested. The treatments were laid out in a randomized complete block design. DAYCENT model was used to simulate soil carbon, N2O emissions and maize yields. Results showed that daily fluxes of N2O ranged between -0.5-26 g ha-1 d-1 and -2-10 g ha-1 d-1 in the long and short rainy seasons respectively. Cumulatively, N2O emissions were between 0.2 - 0.7 kg ha-1 and 0.2 - 0.4 kg ha-1 in the long and short rainy seasons respectively. In the long rainy season, ZT M-S CRU had significantly higher N2O fluxes than the other treatments (P=0.05). In the short rainy season there were no significant effects of treatment on N2O emissions. In the long rainy season, CO2 daily fluxes were between 9 to 42 kg ha-1 while the cumulative emissions ranged between 2.5 to 2.8 t ha -1. In the short rainy season daily CO2 fluxes ranged between 6 to 30 kg ha-1 while cumulative emissions were 1.8- 2.5 t ha -1. There was no significant effect of treatment on CO2 emissions. Methane emissions were largely negative, and did not differ significantly among treatments. Yield was significantly low for ZT M/S but N2O emission intensities were not significantly different among treatments. DAYCENT simulated soil carbon and maize yield within the same ranges observed by measurement. N2O emissions by DAYCENT were higher during the peak of the seasons, but were comparable with observed measurements later in the seasons. Even though the long rainy season had higher N2O and CO2 emissions, the difference was not significant. These results indicate that emissions in the study area were low.These results further indicate that the current soil management practices in Siaya County influence GHG emissions, and the higher emissions observed with ZT M-S CRU in the long rainy season calls for further investigations of the effect of CRU on N2O emissions. The lower emission intensity shown by ZT M/S despite having lower yield points to the need of evaluating cropping systems for climate change mitigation and adaptation. These results indicated that DAYCENT model can be used to simulate soil carbon and yield but not N2O emissions in the study area.
Seed Quality of Soybean (Glycine Max [L.] Merrill) Genotypes under Varying Storage and Priming Methods, Mother Plant Nutrient Profiles and Agro-Ecologies in Kenya
(Kenyatta University, 2015-10) Chirchir, Grace Jepleting
world. The demand for soybeans in Kenya is high yet production is negligible due to various challenges, one of which is lack of a well-organized soybean seed system. Soybean seed has been known to deteriorate rapidly in the tropics but the rates vary with the environment, initial quality of the seed and genotype. The broad objective of the research was to enhance soybean seed longevity and vigor through manipulation of storage and priming methods, mother plant nutrition and agro-ecology. A socio-economic survey was conducted to evaluate soybean enterprise, seed handling and quality in Meru South - Tharaka Nithi County. A seed storage trial was done to assess the effect of agro-ecology, genotype, seed dressing and storage materials on soybean seed longevity and vigor. Soybean genotypes tested Gazelle and TGx 1740-2F(SB19) were dressed with wood ash and Apron star® and stored in sealed plastic cans and synthetic gunny bags in farmers stores at Kirege (UM II) and Igambatuntu (LM IV) in Meru South. Monitoring of seed quality during 8 months of storage was done by moisture content, germination, electrical conductivity and accelerated ageing tests at Genetic Resource Research Institute Laboratory, Muguga. The effects of osmo and hydro-priming seed invigoration techniques on soybean seed quality and storability of primed seed was assessed. The influence of mother plant nutrition, genotype and agro-ecology on soybean productivity and seed quality was carried out at Muguga (LH3) and Nkoroi in (UM4) during the short rains of October-November 2013; and seed quality analyzed using accelerated ageing and electrical conductivity tests. Soybean farmers survey revealed that soybean was grown mostly by older (>40yrs -79%), small scale (0.9Ha) mixed farmers on small parcels (0.05ha) and producing low yields of about 283 kg ha-1 . Soybean was newly introduced (<4yrs - 89%) crop, grown mainly in the short rains (84%) as a pure crop (77%), with main varieties being Gazelle (82%) and TGx 1740-2F (14%). Due to lack of assured markets, the crop was mainly grown for own use (74%) mostly as composite flours. Due to lack of a certified seed, farmers relied on farm-saved-seed, stored in synthetic gunny bags (89%) for 1-8 months, with viability ranging from 0% in the warmer LM4 to 100% in the cooler UM2. The seed storage study showed that hermetic storage in sealed plastic Jeri cans, seed dressing with wood ash and storage in cooler agro-ecologies (UM2) was found to be effective and low cost seed storage method for enhancing soybean seed viability and vigor. Soybean genotype SB19 had higher viability, longevity and vigor than Gazelle. Priming enhanced seed vigor by reducing seed leachates, but reduced germination. The 24 h priming duration and PEG -1.0 Mpa was the most beneficial treatment for SB19 but not for Gazelle. Primed seed retained high vigor after 8 months of post priming storage than non-primed seed. The manipulation of mother plant nutrition genotype and agro-ecology revealed that soybean grown in cooler LH3 had greater longevity and vigor, but with lower yields than seed grown in the warmer LM4; and TGx1740-2F resisted field weathering than Gazelle. Nitrogen and Phosphorus fertilization had no effect on soybean productivity, but N25 and N25+ P60 enhanced seed longevity, but these effects varied with site and genotype. The study recommends establishment of source of quality seed, streamlining marketing and promoting utilization of soybean to enhance production of the crop. Seed dressing with ash and storage in hermetically sealed plastic cans in the cooler highlands is recommended for better seed quality. In addition seed should be produced with good nutrition, in the cooler highlands for enhanced longevity. Priming is recommended for enhancing vigor of SB19.
Soil Moisture Conservation, Cropping Systems and Soil Fertility Effects on Soil and Maize Performance in Machakos County, Kenya
(Kenyatta University, 2019-05) Mwende, Ngie
The main causes of food insecurity in semi–arid parts of Kenya are low soil fertility, low and unreliable rainfall. These two causes are the main challenges facing small-scale farmers in food production especially in semi-arid areas of the country. To overcome these challenges, soil and water management technologies especially those in soil and water conservation need to be embraced. The aim of the study was to determine the effect of tied ridges, fertilizers and cropping systems on soil properties (moisture, pH and organic carbon), growth and yield parameters of maize; and to identify the most cost effective water and soil management technology. This study was carried out in four seasons at Katumani in Machakos County. The experiment was a 2 x 4 x 2 factorial, laid out in a randomized complete block design (RCBD). The treatments were: tied ridging, flat bed planting, farm yard manure 0 t/ha, farm yard manure 5 t/ha, nitrogen fertilizer 20 kg/ha, farm yard manure 5 t/ha + nitrogen fertilizer 20 kg/ha, maize mono crop and maize cowpea intercrop. Data collected included soil moisture content, soil pH, total organic carbon, growth parameters and maize yield. The results showed that, treatments with flat bed planting in maize mono crop significantly increased soil moisture content at 0–20cm depth as compared to tied ridging in maize cowpeas intercrop during short rains 2015. Application of farm yard manure at 5 t/ha increased soil moisture content at 2 and 4 weeks after planting. The soil moisture content ranged from 6.30% to 23.80%. During the short rains 2015, maize mono crop significantly increased vegetative growth in comparison to maize cowpeas intercrop. Treatment with flat bed and 20 kg N/ha in maize mono crop had the highest mean for vegetative growth. However, during the long rains 2016, treatment with tied ridging and 20 kg N/ha in maize mono crop registered the highest mean for vegetative growth. During the short rains 2015, treatments with maize mono crop significantly increased grain yield with a range of 1.35 t/ha 3.59 t/ha. Flat bed planting with farm yard manure 5 t/ha in maize cowpea intercrop significantly increased the grain yield by 165.93%. The harvest index during the short rains 2015 ranged between 0.35 and 0.48. Treatments with maize mono crop significantly increased gross benefit, net profit, gross margin and cost benefit ratio during short rains 2015 and long rains 2016. Application of farm yard manure 5 t/ha + 20 kg N/ha had the highest variable cost. The cost benefit ratio was positive during the short rains 2015 with a range of 1.47–2.98. The yield differences among the four seasons could have been as a result of variations/distribution in rainfall amount, soil moisture content and soil fertility as induced by the treatments. Flat bed planting increased the yields during the short rains 2015 when the amount of rainfall was high whereas tied ridging resulted in improved yields during short rains 2014, long rains 2015 and 2016 when rainfall amount was low. For the farmers to maximize yields and profits in the study area, adoption of flat bed planting with farm yard manure 5 t/ha and maize cowpeas intercrop during the seasons of high rainfall could be appropriate treatment combination according to the findings of this study. However, during seasons with low rainfall, tied ridging with 20 kg N/ha and maize mono crop could be recommended for adoption. Also, variations in seasonal rainfall should be considered when integrating different soil and water management practices because the effectiveness of different technologies vary with the seasons. Farmers in Machakos County may have to consider use of supplementary irrigation during the dry spells to increase soil moisture.

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