PhD Thesis: Department of Water and Agricultural Resource Management

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    Determination of Factors Influencing the Efficiency of Legume Green Manures for Maize Production in Embu, Kenya
    (Kenyatta University, 2008-05) Gitari, Josiah N.
    Land productivity in the central highlands of Kenya is mainly constrained by low and declining soil fertility. In the maize-based farming systems, continuous cultivation without adequate soil fertility enhancement measures has led to a deterioration of land quality resulting in low agricultural yields and degraded soils. Herbaceous legumes can provide an alternative to commercial fertilizers and animal manures. This study explored the use of these legumes in Embu District - situated within the central highlands of Kenya. In order to achieve this objective a survey and four field experiments were conducted to: (1) Validate farmers’ knowledge and practices in soil fertility and use of plant residues; (2) Determine the performance of maize and green manure herbaceous legumes under different intercropping densities and relay-cropping regimes; (3) Investigate the relative efficiency of different legume residue management techniques and determine the need for mineral nitrogen (N) supplementation and (4) Determine the role of low quality plant residues as agents for slowing down the fast-decomposing legume residues to improve N synchrony for maize growth. The study consisted of one survey and four on-station field experiments. The survey involved a total of 134 small-scale farmers cutting across 5 major agro-ecological zones of the 30 km transect of the district. About 87 per cent of all the farmers in the district were affected by the problems of low soil fertility in their farms. Farmers gave soil colour and structure as some of the visual soil fertility assessment indicators used to determine soil fertility status in their farms but the most pronounced and elaborate local indicators seemed to be the dominance of certain weed flora. Soil pH and exchangeable bases (Ca++ and Mg++) were the most sensitive laboratory soil parameters that corroborated farmers’ perceptions and knowledge of soil fertility. Results of the field experiments showed that it is feasible to intercrop maize with any of the three green manure legume species, namely, mucuna [Mucuna pruriens (L.) DC. Var. utilis (Wright) Bruck], crotalaria [Crotalaria ochroleuca G. Don] and lablab [Lablab purpureus (L) Sweet cv. Rongai]. Relay-cropping these green manure legumes (GML) beyond the second week after maize emergence had a significant reduction on legume biomass production possibly due to reduced photosynthetically active radiation (PAR) under the maize canopy. Intercropped GML intercepted less than 30 per cent of the total incident radiation. Nonetheless, intercropping of maize and GML greatly improved land productivity giving relative yield total (RYT) values of between 1.0 and 1.5. Incorporation or surface mulching of the GML residues gave similar maize yield responses that was about double that of the control (no residues). Supplementation of the GML residues (raised in situ) with mineral N was only beneficial if the quantities incorporated were below 2.0 Mg ha-1 . Maize grain yield after mucuna, crotalaria and lablab residues alone (no mineral N supplemented) was 2.5, 2.3 and 1.6 times higher, respectively, than those of the control. Soil N mineralization reached a peak 4 weeks after planting (WAP) and declined thereafter until 8 WAP before picking up again for the remainder of the season. Seasonal mineral N levels ranged between 40 to 128 kg N ha-1 . Plots treated with GML residues gave significantly higher total N uptake than the untreated plots. Over the 3 year period, legume residue incorporation resulted in a slight reduction (0.9-1.8%) in soil bulk density, a small increase in the soil total N but no change in the soil pH. Addition of low quality residues (maize stover) to any of the three GML residues did not affect N release but appeared to enhance their performance. Soil mineralization and maize N uptake was not affected by the addition of low quality residues to the GML residues but resulted in a small increase in the total soil N and pH. However, addition of large quantities of these low quality residues (6.0 Mg ha-1 ) significantly increased the soil organic carbon by 13 per cent and also decreased the soil bulk density by 8.3 per cent when compared to the absolute control with no residues added.
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    Mapping and managing the spread of Prosopis Juliflora in Garissa County, Kenya
    (Kenyatta University, 2011-06) Zeila, Abdi
    More than three decades after the introduction of prosopis species in the drylands of Kenya there is now increasing concern about the negative impacts of the plant on the livelihoods of dryland communities and on the ecological integrity of the fragile arid and semiarid lands. The extent of the species coverage in the arid and semiarid lands has, however, not been fully mapped owing in part to the recent nature of the problem. As such the aim of this study was to map out the extent of the spread of the species and propose community-friendly management options for this invasive plant. Geographic information system methodology and satellite imageries (Landsat images from 2000 and 2006), maps and GPS points were the main tools used for this work. Standard spatial statistical analysis procedures were employed using the software Erdas Imagine 8.4 and ESRI ArcView to generate land cover changes associated with prosopis species. The study found that a total of 440 square kilometres were newly colonised between the years 2000 and 2006, with Bura division having the highest area of land colonised at 143km² (33% of total land area). The study also noted that the riverine land use/land cover system was the most infested, with 631km2 colonised. This automatically puts the livelihoods of thousands of pastoralists who depend on the River Tana ecosystem at risk. The study also employed a socio-economic survey that involved the use questionnaires and interviews to ascertain the perceptions of the local community regarding origin, impact and uses of the species. Eighty four per cent of the respondents indicated that prosopis’ presence has had negative effect on the indigenous biodiversity of Garissa through loss of native vegetation. The three major local uses of prosopis were charcoal, fuelwood and animal fodder. The study shows that prosopis is a major environmental problem in the study area through its swift colonisation of strategic grazing reserves and is rapidly colonising new lands. The findings of this study call for commercialising production of prosopis for charcoal burning as a strategic management strategy for the plant. This should be accompanied with the use of efficient kilning technologies. In addition deliberate and pro-active policy changes should be put in place to delineate land specifically for this environmental business. Spread of the plant outside designated areas should be controlled by use of environment-friendly mechanical approaches. This further calls for community capacity building in partnership with key stakeholders like Kenya Forest Service. In this way, prosopis will cease to be a liability and instead contribute to community development through wealth creation.
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    Effects of Irrigation and Nitrogen Fertilizer Levels on Water and Nitrogen Use Efficiency and Yield of Drought Tolerant Hybrid Maize (Zea mays L.) in Embu County, Kenya
    (2019) Onyari, Charles N.
    Food grain shortage in Kenya is attributed to low rainfall and poor distribution in maize growing areas particularly as well as low soil fertility associated mainly with nitrogen deficiency. Use of irrigation water and nitrogen fertilizer is likely to solve this food security challenge. This study was conducted over two seasons covering 2012 and 2013 with the aim of establishing optimal irrigation and nitrogen fertilizer rates for drought tolerant hybrid maize (Zea mays L.), DK8031, grown in furrows to optimize rainfall capture with the objective of simultaneously achieving high water and nitrogen use efficiencies and yields. Four irrigation levels allocated as main plots were given: I119 - only once at sowing with 119 mm; I2 = 238 mm - at sowing and two weeks after sowing (WAS); I357 – at sowing followed by applying at two and six WAS; I476 - at sowing, followed by applying at two, six and ten WAS. These totaled to 119.05, 230.10, 357.15 and 476.2 mm of applied irrigation water, respectively, exclusive of the 542.4 and 780.0 mm seasonal rainfall received in 2012 and 2013. Nitrogen was allocated to the subplots incrementally at N0 = 0, N30 = 30, N60 = 60, N90 = 90 and N120 = 120 kg-N/ha application rates. It was observed that application of irrigation water and nitrogen positively and significantly affected biomass and grain yields as well as the yield components of the DK8031 maize variety. The highest dry matter and grain yields of 13,200 and 4,000 kg/ha were obtained with 476.6 mm applied irrigation water and 120 kg/ha nitrogen rate. The aboveground biomass and grain yields varied from 11.8 to 16.3 and 3.7 to 4.0 t/ha. The highest number of cobs per ha (47,500 to 62,778 cobs/ha), cob length (17.5 to 19.9 cm) and lines per cob (12.9 to 13.4) were achieved at I476N120 treatment combination in both season and increased with additional inputs, implying higher production potential at higher values of irrigation levels and fertilizer rates. The biomass and grain based water use efficiencies decreased with increase in irrigation but increased with increasing nitrogen rates and ranged from 8.2 to 12.8 kg-DM/ha-mm and 4.3 to 4.4 kg-grain/ha-mm in Season I and II, respectively. Linear and quadratic production functions developed predicted yields with high certainties (R2) ranging between 0.60 and 1.00. Optimal yield was obtained with 357 mm supplemental irrigation water and 90 kg-N/ha of application nitrogen. Farmers in Embu can grow the DK8031 maize with at least 238 mm and 357 mm depth of supplemental irrigation at nitrogen rates of 90 and 100 kg/ha to promote productivity of the crop in the October to March and April to September seasons, respectively.
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    Environmental greenhouse gas hotspots and climate change adaptation in smallholder sorghum cropping systems in Siaya county, Kenya
    (COLLINS MUIMI MUSAFIRI, 2020-09) Musafiri, Collins Muimi
    Sorghum (Sorghum bicolor L.) is an essential drought-resistant crop that could enhance food security. However, its productivity remains relatively low in Kenya. Efforts to increase sorghum productivity through the application of external inputs could increase greenhouse gas (GHG) emissions. The study aimed to assess environmental GHG emission hotspots, effects of minimum tillage and inorganic fertilizer adoption on sorghum yields, and the determinants of adopting climate-smart agriculture and climate change adaptation practices. The study employed a cross-sectional survey of 300 smallholders in Siaya County, Kenya. Principal component analysis and hierarchical clustering were used in farm typologies construction. Using Cool Farm Tool software, a carbon footprint assessment approach was performed to identify environmental GHG emissions hotspots. One-way analysis of variance was used to test the influence of farm types on sorghum yields, GHG balance, carbon footprint, and monetary footprint in SAS 9.4 software. Descriptive statistics were used to describe the survey data. The impact of minimum tillage and inorganic fertilizer adoption were analyzed using propensity score matching and endogenous switching regression. Socioeconomic, institutional and biophysical determinants of adopting climate-smart agricultural practices (CSAPs) were analyzed using multivariate and ordered probit regression. Binary and Poisson regression models were used to evaluate the determinants of adopting climate change adaptation strategies. The results showed five farm types. The study showed that sorghum cropping systems were net sinks of soil GHGs. The GHG balance, carbon footprint, and monetary footprint significantly varied across the farm types at p=0.025, p=0.018, and p=0.004, respectively. The GHG balance ranged from -818.76 kg CO2 eq. ha-1 in manure intensive and low fertilizer intensity small farms to 174.29 kg CO2 eq. ha-1 in fertilizer intensive and moderate manure application rates on small farms. Adoption of minimum tillage and inorganic fertilizer improved sorghum yields. The study showed both complements and substitutes between CSAPs. The multivariate probit analysis revealed that the household head's gender, education, age, family size, contact with extension agents, weather information, arable land, livestock owned, perceived climate change, infertile soil, and persistent soil erosion influenced CSAPs adoption. Gender, arable land, livestock owned, soil fertility, and constant soil erosion were crucial determinants of CSAPs adoption intensity. Membership in agricultural associations, study location, progressive farming, literacy, remittance, access to credit, farm size, weather forecast information, and perceived climate changes significantly determine the adoption of climate change adaptation strategies. The study revealed that the judicious integration of inorganic fertilizers with animal manure could significantly improve sorghum yields while reducing yield-scaled greenhouse gas emissions. The findings on adopting agricultural innovations have incredible implications on rural livelihood. Enhanced productivity could promote food security and improve purchasing power, thus enhancing smallholder farmers’ capacity to cope with declining soil fertility and climate change-related challenges.
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    Genetic Diversity of Alternaria solani and Phytophthora infestans isolates and their Management using crude Extracts and Essential Oils of Selected Plants in Kenya
    (University of Embu, 2021-07) Mugao, Lydia Gakunyi
    Kenya is rated 6 in Africa with an annual overall production of 397,007 tons of tomato fruit. Tomato production in Kenya is constrained by many biotic and abiotic factors and among them, diseases such as early and late blight caused by Alternaria solani and Phytophthora infestans, respectively. Farmers use synthetic chemicals to manage the diseases. However, there has been major concern because they are costly, toxic to human beings and the environment. Some of the products have been rejected in the international markets because of high chemical residue levels. Some of the pesticides have not been effective because of the pathogens undergoing genetic mutations that result to resistant strains. This study sought to assess the genetic diversity of pathogens causing early and late blight in tomato and their management using plant extracts and essential oils from selected plants. Isolation of A. solani and P. infestans was done from infected tomato plant samples collected from Mwea, for morphological and molecular characterization. Crude extracts and essential oils of garlic, ginger, Mexican marigold and tick berry were tested in-vitro to determine their efficacy against the two pathogens. Alternaria solani and P. infestans were cultured in Potato Dextrose Agar and V8 agar respectively after amending the media with different plant extracts and essential oils. Pathogen radial growth was monitored per treatment over time. Tomato plants were grown in the greenhouse and inoculated with spores of cultured isolates of A. solani and P. infestans. The inoculated plants were sprayed with essential oils and ridomil th synthetic fungicide as a control and disease development was monitored. Data collected was subjected to analysis of variance to test for statistical significance among treatments. Means were separated using Students Newman Keuls test at 95% level of confidence. Molecular characterization of the pathogens showed that A. solani had high genetic variation, while P. infestans showed low genetic diversity. Characterization of the essential oil compounds revealed that the test plants had many compounds and terpenes were the majority. The in-vitro experiment revealed that both the crude extracts and the essential oils were fruitful in suppressing the growth of the test pathogens. However essential oils were more effective than the crude extracts (p<0.05). Among the crude extracts, garlic was the most effective biocontrol. Ginger and garlic essential oils had similar effect to Ridomil  synthetic fungicide (Metalaxyl-M and S-isomer, Mancozeb) which showed 100% pathogen growth inhibition. In the greenhouse experiment, essential oils and Ridomil  synthetic fungicide did not differ significantly (p>0.05) in lowering disease severity. The tomato plants treated with Mexican marigold had the highest plant height (78.208±1.28) and also the highest number of leaves (20.5±0.93) in plants inoculated with P. infestans. The treatment also exhibited the highest fruit yields. The effects of other treatments did not vary significantly (p>0.05). Essential oils used in the greenhouse experiment had similar effects to Ridomil fungicide and therefore can be tapped for their antimicrobial efficacy. This study concluded that there exists genetic variation within A. solani than in P. infestans in Mwea, Kenya. The source of variation within them needs to be studied. This study recommends that plant extracts and essential oils from ginger and garlic be used as bio-pesticides in management of early and late blight diseases in tomato as they portrayed similar efficacy to ridomil synthetic fungicide. Simpler and cheaper methods of essential oil extraction can be explored to make the oils available for use as pesticides.
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    Combining ability and genetic mappig of pod quality and yield traits in locally adapted french beans (phaseolus vulgaris l.) in Kenya
    (UoEm, 2025-06-03) Njau, Serah Nyawira
    French beans are common beans (Phaseolus vulgaris L.) that have palatable pods. The crop is mostly grown for export, supporting Kenyan smallholder farmers. In Eastern Africa, developing French bean varieties with high pod yield, good pod quality, and processing industry has received little research, and there is limited information on genetics of pod quality and yield traits. This study investigated the genetics underlying French bean pod quality and yield, with crucial characteristics for the development of improved varieties in Kenya. The first objective focus was on evaluation of commercial French bean varieties for pod quality and yield performance. Thirteen French bean and two dry bean varieties were tested for pod quality and yield in Embu and Mwea, to select material for further research. Later, a half-diallel population was developed from five French bean and two dry bean varieties. The aim was to examine the gene action of French bean pod attributes and to identify parents with good combining abilities. Additionally, a cross between French bean × dry bean, was used to develop a population of recombinant inbred lines (RILs) specifically using the Vanilla × MCM5001 varieties, to facilitate genetic mapping of traits associated with French bean pod quality and yield. Data on various pod traits of the RILs and parents were collected from plants that were planted in three trials in Kenya and the University of California, Davis greenhouse. In addition, genomic DNA from the RILs and parents were genotyped using single nucleotide polymorphisms (SNPs). Results from diallel analysis revealed significant (P < 0.001) general and specific combining abilities effects for the evaluated traits. This highlighted the significance of additive and dominance gene effects, with the predominance of additive gene effects. The crosses between Serengeti × Amy, Serengeti × Moonstone, and Serengeti × G2333 were best combiners for pod quality, whereas G2333 × Amy and Moonstone × Amy produced best progenies for pod yield. Using SNPs and phenotypic data from 184 F2:6 RILs, 44 quantitative trait loci (QTL) were discovered for yield and pod quality traits through QTL mapping. The QTL for pod yield were identified on chromosomes Pv03 and Pv08, while the QTL for pod quality were located on chromosomes Pv01, Pv02, Pv03, Pv04, Pv06, and Pv07. In addition, six novel QTL were identified, whereas others overlapped with pod quality and yield QTL. Using the mapping results, candidate genes responsible for French bean pod string (St) were identified and eight gel-based molecular markers were developed and tested for their suitability for marker-assisted selection (MAS). The results indicated that six of the eight markers amplified DNA from Vanilla and MCM 5001, although only one marker revealed variation between the parents and RILs. Chi-square analysis identified a significant (P < 0001) association between the pod string score and the marker, linked at 7.8 cM from St. The identified QTL and markers can facilitate development of more robust molecular markers and for further studies on French bean pod quality and yield. In addition, varieties with the best combining abilities (Serengeti × Moonstone, MCM 5001 × Amy and Vanilla × Moonstone) can serve as parents in breeding initiatives that focus on improving French beans in Kenya.