DSpace Repository :: Browsing by Author "Nyaga, Justine M."

Browsing by Author "Nyaga, Justine M."

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Anti-inflammatory norhopanes from the root bark of Fagaropsis angolensis (Engl.) H.M.Gardner
(Elsevier, 2020-06-17) Nyaga, Justine M.; Mukavia, Justus; Omosa, Leonidah Kerubo; Ngnitedemb, Vaderament Nchiozem; Omoled, Ruth; Bitchagnoc, Gabin Thierry M.; Spitellere, Michael
Two new norhopane derivatives namely 3β,6β,22-trihydroxy-7β,11α-di[(4-hydroxybenzoyl)oxy]-21αH-24- norhopa-4(23)-ene (1) and 3β,6β,22-trihydroxy-7β-[(4-hydroxybenzoyl)oxy]-21αH-24-norhopa-4(23)-ene (2) together with two previously reported compounds, including a norhopane, 3β,6β,11α-trihydroxy-7β-[(4-hydroxybenzoyl) oxy]-24-norhopa-4(23),17(21)-diene (3) and a norneohopane, (21αH)-24-norneohopa-4(23), 22(29)-diene-3β,6β,7β-triol 7-caffeate (4) were isolated from the root bark of Fagaropsis angolensis. Elucidation of their structures was achieved by spectroscopic (NMR, IR and UV) and spectrometric (HRESIMS) data and by comparison of these data with those of related compounds in the literature. Compounds 1–4 were evaluated for their anti-inflammatory activity by measuring the levels of cytokines, IL-1β, IL-2, GM-CSF and TNF-α in lipopolysaccharide (LPS) stimulated peripheral blood mononuclear cells (PBMC). All tested compounds decreased secretion of IL-1β and TNF-α. Compounds 2 and 4 caused significant decrease of the production of IL-2, GM-CSF and TNF-α compared to the reference drug, ibuprofen. These findings showed that the root barks of F. angolensis are rich source of norhopane derivatives and further provide a scientific rationale of using this plant in Kenyan folk medicine to relieve pain.
The Contribution of Occult Precipitation to Nutrient Deposition on the West Coast of South Africa
(2015-05) Nyaga, Justine M.; Neff, Jason C.; Cramer, Michael D.
The Strandveld mediterranean-ecosystem of the west coast of South Africa supports floristically diverse vegetation growing on mostly nutrient-poor aeolian sands and extending from the Atlantic Ocean tens of kilometers inland. The cold Benguela current upwelling interacts with warm onshore southerly winds in summer causing coastal fogs in this region. We hypothesized that fog and other forms of occult precipitation contribute moisture and nutrients to the vegetation. We measured occult precipitation over one year along a transect running inland in the direction of the prevailing wind and compared the nutrient concentrations with those in rainwater. Occult deposition rates of P, N, K, Mg, Ca, Na, Al and Fe all decreased with distance from the ocean. Furthermore, ratios of cations to Na were similar to those of seawater, suggesting a marine origin for these. In contrast, N and P ratios in occult precipitation were higher than in seawater. We speculate that this is due to marine foam contributing to occult precipitation. Nutrient loss in leaf litter from dominant shrub species was measured to indicate nutrient demand. We estimated that occult precipitation could meet the demand of the dominant shrubby species for annual N, P, K and Ca. Of these species, those with small leaves intercepted more moisture and nutrients than those with larger leaves and could take up foliar deposits of glycine, NO3-, NH4+ and Li (as tracer for K) through leaf surfaces. We conclude that occult deposition together with rainfall deposition are potentially important nutrient and moisture sources for the Strandveld vegetation that contribute to this vegetation being floristically distinct from neighbouring nutrient-poor Fynbos vegetation.
The Contribution of Occult Precipitation to Nutrient Deposition on the West Coast of South Africa
(2015-05-27) Nyaga, Justine M.; Neff, Jason C.; Cramer, Michael D.
The Strandveld mediterranean-ecosystem of the west coast of South Africa supports floristically diverse vegetation growing on mostly nutrient-poor aeolian sands and extending from the Atlantic Ocean tens of kilometers inland. The cold Benguela current upwelling interacts with warm onshore southerly winds in summer causing coastal fogs in this region. We hypothesized that fog and other forms of occult precipitation contribute moisture and nutrients to the vegetation. We measured occult precipitation over one year along a transect running inland in the direction of the prevailing wind and compared the nutrient concentrations with those in rainwater. Occult deposition rates of P, N, K, Mg, Ca, Na, Al and Fe all decreased with distance from the ocean. Furthermore, ratios of cations to Na were similar to those of seawater, suggesting a marine origin for these. In contrast, N and P ratios in occult precipitation were higher than in seawater. We speculate that this is due to marine foam contributing to occult precipitation. Nutrient loss in leaf litter from dominant shrub species was measured to indicate nutrient demand. We estimated that occult precipitation could meet the demand of the dominant shrubby species for annual N, P, K and Ca. Of these species, those with small leaves intercepted more moisture and nutrients than those with larger leaves and could take up foliar deposits of glycine, NO3-, NH4 + and Li (as tracer for K) through leaf surfaces. We conclude that occult deposition together with rainfall deposition are potentially important nutrient and moisture sources for the Strandveld vegetation that contribute to this vegetation being floristically distinct from neighbouring nutrient-poor Fynbos vegetation.
Do afroalpine plants differ from other alpine plants by their leaf functional traits?
(UoEm, 2023-06-16) Onipchenko, Vladimir G.; Kipkeev, Aliy M.; Kopylova, Natalia A.; Nyaga, Justine M.; Elumeeva, Tatiana G.; Dudova, Ksenia V.; Akhmetzhanova, Asem A.; Tiunov, Alexei V.; Karpukhin, Mikhail M.; Makarov, Mikhail I.
Afroalpine plants develop under specific climate with great daily fluctuations and weak seasonal dynamics of temperature. Do leaf functional traits of the plants in Mt. Kenya differ from those of temperate plants in NW Caucasus? To answer this question, we conducted a comparative study at the Teleki valley (4000–4500 m a.s.l.), Mt. Kenya, Kenya, and Teberda national park (2600–2900 m a.s.l.), the Caucasus, Russia. We measured leaf area, fresh and dry mass, C, N, P, δ 13 C, δ 15 N and derivative traits (specific leaf area – SLA, leaf dry matter content – LDMC, C:N and N:P ratios) for 48 species at the Teleki valley, and the same traits, except for the δ 13 C and δ 15 N, for 141 species in the Teberda national park. The CSR-stra tegies scores were calculated. We applied the Principal Component Analysis to reveal the main patterns of trait variation. Leaf dry mass of Mt. Kenya alpine plants ranged from 0.27 mg (Sagina afroalpina) to 14.0 g (Dendrosenecio kenio den dron). Leaf area, mass and LDMC of alpine plants in both regions did not differ significantly. The SLA of Mt. Kenya’s plants varied about 20-fold: from 2.6 mm 2 mg -1 (Festuca pilgeri) to 39.8 mm 2 mg -1 (Cineraria deltoidea), and Caucasian plants had higher SLA. N and P leaf concentrations were higher, but C lower in Caucasian plants than in Kenyan. Leaf N:P ratio was similar for both regions, while C:N ratio was higher in Kenyan plants. Species of “rosette” trees (Dendrosenecio spp.) differed from other species by size characteristics (maximal leaf dry mass and area were in Dendrosenecio kenioden dron), as well as correspondingly higher investment to mechanical tissues (high C:N ratio, low SLA). By the other functional traits, “rosette” trees were similar to many other alpine plants. Thus, afroalpine plants of Mt. Kenya are close to temperate alpine plants by some leaf functional traits, but possess higher stress-tolerance.
Empirical and model derived respiration responses to climate in different soils of an arid South African ecosystem
(The University of the Western Cape, 2009) Nyaga, Justine M.
This study examined the magnitude of soil CO2 efflux in an arid South African ecosystem, the flux responses as well as those of key limiting nutrients to soil temperature increases and moisture reductions consistent with a future climate change scenario, and compared measured soil respiration rates with those predicted with empirically and theoretically-based soil respiration models. Measurements of soil respiration rate, temperature, moisture, N and P contents were conducted monthly over a 12-month period in natural environments and those artificially manipulated with replicated open-top warming chambers (average 4.1oC increase) and precipitation exclusion chambers (average 30.1% decrease in rainfall, 26.2% decrease in fog and dewfall) distributed in five different soil-vegetation units.Measured soil respiration rates were over 3-fold less than those reported for temperate and tropical forest ecosystems with 61.5% of the total soil CO2 efflux contributed by root respiration (derived from the differences between moderately vegetated and sparsely vegetated areas) in moderately vegetated soils. Massive increases (up to 15 times) in soil CO2 efflux occurred during wet phases, but even these large CO2 pulses were only comparable in magnitude with soil CO2 effluxes reported for temperate semi-arid grasslands. There was considerable intra-annual and inter-site variability in the magnitude and direction of soil respiration and N and P responses to elevated temperatures and reduced precipitation levels with poor correspondence evident between soil CO2 efflux and soil organic matter content. Soil CO2 effluxes declined in response to precipitation exclusion by 7.1% over all sites and increased in response to warming by 42.1% over all sites. The large increase in response to warming was assisted by a 7.5% enhancement in soil moisture content due to precipitation interception by the chamber walls and its channelling to the soil surface.Relatively smaller respiration increases in response to warming occurred in moderately vegetated soils, these attributed to soil thermal insulation by the plant canopy cover. Soil P and N contents increased in response to warming by 11.3% and 13.3% respectively over all sites, with soil P declining in response to precipitation exclusion by 5.8% over all sites and soil N increasing in response to precipitation exclusion over all sites by 5.8%. Standard least squares regressions quantified the relationships between soil respiration rate and measured soil physical and chemical properties, and their interactions for each of the 5 soil-vegetation units. These relationships were incorporated in an empiricallybased soil respiration (EMR) model which was compared with a theoretically based generalized soil respiration model (GRESP). GRESP model functions included measured Q10 coefficients at soil moisture contents above field capacity, these assumed reduced by half for dry conditions, and maximum retentive and field capacities of soils. EMR modelled soil respiration rates displayed slightly better correspondence with measured soil respiration rates than GRESP modelled soil respiration rates. This apparent from the higher regression coefficients and lower sums of squared residuals, with EMR model residuals also more closely approximating normal distributions. However, despite the EMR model’s slight superiority, it was concluded that more precise laboratory-based measurements of soil retentive and field capacities and their Q10 coefficients at different soil moisture contents could improve the GRESP model’s accuracy thereby providing a more convenient and uncomplicated means of predicting respiration responses to current and future climates over a wide range of arid soil types
Food web structure of nematode communities in irrigated rice fields
(Heliyon, 2023-02) Mokuah, Dorcas; Karuri, Hannah W.; Nyaga, Justine M.
Nematodes are a key component of the soil food web and they play an important role in the provision of ecosystem services. Rice cultivation in Mwea, Kenya involves the intensive use of fertilizers and pesticides which may affect the complexity of the nematode-based soil food web. This study examined the nematode diversity and food web structure in irrigated rice fields in Nyangati and Tebere in Mwea, Kirinyaga County, Kenya. Nematodes were identified up to the genus level and soil physico-chemical properties were also determined. Aphelenchoides and Longidorus occurred in significantly greater proportions in Tebere, while in Nyangati there was a high abundance of Helicotylenchus. Aphelenchoides was positively correlated to soil electrical conductivity. From additive diversity partitioning of genus richness, the α and β components contributed 33.7% and 66.3% of the γ diversity, respectively. For Shannon and Simpson diversity indices, the largest contribution to overall diversity was from α component. Soil food web indices were similar across the two regions. Channel and basal indices were below 30% while Enrichment (EI) and Structure (SI) indices were above 50%. There was no variation in metabolic footprints except for the fungivore footprint which was significantly higher in Tebere. Based on the EI and SI, the soil food web in paddy rice fields in Mwea was structured and enriched with moderate disturbance. Due to the high prevalence of economically damaging parasitic nematodes in the rice fields, appropriate management schemes that enhance specific components of the soil food web and increase the suppressive ability of soil against plant-parasitic nematodes should be implemented.
Human-Wildlife conflicts at the interface between Mt. Kenya National Park/National Forest and small holder farming communities in Embu County
(Swedish University of Agricultural Sciences, 2021-06) Nyaga, Justine M.; Rock, Kim; Kjellander, Petter
Human-wildlife conflict (HWC) is a common problem for many farming communities around protected areas like parks, reserves and forests all around the world. In Kenya where most farming occurs at smallholder levels, HWC:s could be highly significant as it may lead to a complete loss of crops and livestock. Such cases have previously been experienced by smallholder farming communities around Mt. Kenya national park/natural forest, but many have gone unreported. To minimise these conflicts, the government of Kenya, in collaboration with the Rhino Ark Foundation have constructed an electric fence around the forest. The main aim of this study was to collate and document experiences of crop raiding by wildlife on small holder farms in Embu County, Kenya that are adjacent to the forest. It also aimed at evaluating the effectiveness of the electric wildlife fence along the forest line through Embu County. To achieve this, questionnaires were administered to 181 small holder farmers living and farming within 5 km of the electric fence on the approximately 60 km long forest line. The questionnaires sought to gather information on the wildlife species causing damages, the magnitude of damage suffered by the farmers on the crops and livestock before and after the construction of the fence, the interventions they have in place to prevent such damage and other suggestions to prevent wildlife raids. Wildlife cameras were also used to track wildlife activity at night time. A total of 169 questionnaires were retrieved and 455 pictures downloaded from the cameras. Results show that the percentage of crops destroyed by wildlife was significantly higher in the year before the wildlife fence was constructed in 2016 compared to the period after the fence (2016-19). Currently the naked mole rat (Heterocephalus glaber) and the Kenyan African (Tachyoryctes ibeanus) were reported as the most frequent pests on crops after the fence construction. Elephants were the most severe crop raiders before the fence construction, but their raiding ceased completely after the fence installation. The white tailed mongoose (Ichneumia albicauda) and eagles (Accipitridae family) were the most frequently reported raiders on livestock. Maize, macadamia and bananas were the most commonly targeted crops while chickens were the most targeted livestock. Over 90% of the farmers indicated that the fence significantly contributed to a reduction of HWC:s. However, they also suggested additional fencing for both crops and livestock, as well as trapping and poisoning of raiders like moles and mongooses that were responsible for most of the crop damage and livestock attacks. This study recommends that farmers devise innovative ways of dealing with the threat of small animals. These may include aggressive fencing and growing crops and keeping livestock that are not targeted by small animals. It is also recommends that the Kenya Wildlife Service (KWS) develop innovative ways of compensating affected farmers and prevent further loss. The KWS may also train farmers on procedures to follow in reporting cases of wildlife invasion and on food choices of various wildlife species inhabiting the forest so that they avoid growing crops or keeping livestock that are prime targets for wildlife.
In vitro anti-cancer efficacy and phyto-chemical screening of solvent extracts of Kigelia africana (Lam.) Benth
(Cell press, 2021-01-25) Nyaga, Justine M.; Mukavi, Justus Wambua; Mayeku, Philip Wafula; Kituyi, Sarah Naulikha
Background and objectives: Kigelia africana is a medicinal plant growing naturally in many parts of Africa. In Kenya, a water concoction of the plant is used to treat breast and prostate cancers. Laboratory data on its anti-cancer activity and active principles is limited, hence no scientific rationale for its medicinal use. This study reports on in-vitro toxic activities of dichloromethane and methanol extracts of the plant against human breast cancer cells and phytochemical screening of the two extracts. Methodology: Plant extracts were obtained by sequential solvent extraction of dry plant material (stem bark) using analytical grade dichloromethane: methanol (1:1) and methanol (Sigma Aldrich). In-vitro anti-cancer activities of the extracts were determined using the suphorhodamine (SRB) assay against a human breast cancer cell line (HCC 1937). Preliminary Thin layer chromatography of plant extracts was done using POLYGRAM® SIL G/UV254 plates (Merck) to establish presence of different classes of secondary metabolites. Results: In-vitro cytotoxic activities of the two extracts were significantly different (P ¼ 0.05). The methanol extract exhibited higher activity (IC50 ¼ 26.02 μg/ml) compared to that of dichloromethane: methanol (1:1) (IC50 ¼ 55.01 μg/ml). Phyto-chemical screening of the two extracts revealed the presence of terpenoids, phenols, steroids and flavonoids. Conclusion: The high in-vitro anti-cancer activities of solvent extracts of Kigelia africana justify its use in traditional medicine to manage breast cancer. Phytochemical analysis of the extracts reveal similar profiles hence the differences in their anti-cancer activities can be attributed to quantitative variations of various classes of secondary metabolites.
Influence of drought on interactions between Rhopalosiphum padi and ground dwelling predators – A mesocosm study
(Wiley, 2021-05) Njue, Martin; Muturi, Phyllis W.; Nyaga, Justine M.; Jonsson, Mattias
Climate change will lead to extreme droughts, but it is difficult to predict how this will affect crop pests. In particular, it is unclear how interactions between natural en- emies and pests will be influenced. In the field, bird cherry- oat aphids (Rhopalosiphum padi (L.)) have been observed to reside close to, or below the ground surface during dry conditions. We hypothesized that this will increase the niche overlap between R. padi and ground- dwelling predators such as carabid beetles and wolf spiders and that aphid numbers will therefore decline during dry conditions. A fully factorial mesocosm experiment was conducted testing the combined effects of drought and predator presence on aphid position and abundance on barley (Hordeum vulgare) plants. In support of our hypothesis, we found that (a) aphids moved below ground during dry conditions, (b) predators reduced aphid numbers, but only during dry conditions, and (c) predators reduced the proportion of aphids below ground in dry conditions. This increased predation effect during dry conditions was, however, compensated for by a corresponding increase in aphid performance on the plants and so the net effect of drought on aphid numbers ended up being neutral. Thus, pests can be affected by drought in complex ways via a combination top- down and bottom- up mechanisms. Predicting how pest populations will be affected by droughts in the future is thus a formidable research challenge.
International Journal of Environment and Climate Change
(2020-12-21) Nyaga, Justine M.; Nyaga, Samuel K.; Gathungu, Geofrey K.; Njeru, Jafford R.
Africa is under pressure from climate stresses and is highly vulnerable to the impacts of climate change. In Kenya, agriculture is the backbone of the economy making it an important contributor to food security of rural households. Currently crop productivity is being affected by continued climate variations and decline in soil fertility. Adaptation to climate change requires to be given high and urgent priority for sustainable crop production. A study was conducted in Mavuria ward, Mbeere South Sub-County, Embu County to evaluate the effects of climate change adaptation on crop production. The study used both descriptive and experimental research designs. The primary data on adaptation measures was collected from farmers and institutions using questionnaires. In the data analysis, descriptive statistics were used to organize the climate data and that of the respondents into frequencies. Further, a Pearson correlation test was done to determine the relationship between farmer and institutional based mechanisms on adaptation to climate change at α=0.05. The main adaptation mechanisms identified were soil fertility improvement, soil and water conservation, early planting, pest and disease control, provision of certified seeds, and awareness creation. In view of these findings, the study recommends continuous implementation of these measures that can help strengthen farmers and institutional adaptation mechanisms towards climate change for improved crop production.
Is leaf pubescence of Cape Proteaceae a xeromorphic or radiation-protective trait?
(CSIRO Publishing, 2012-03) Skelton, R. P.; Midgley, J. J.; Nyaga, Justine M.; Johnson, S. D.; Cramer, M. D.
Although pubescence has traditionally been considered to be related to the water economy of plants, the results are ambivalent and vary between different species. We tested two contrasting hypotheses for the functional significance of leaf pubescence of Proteaceae species from the Cape Floristic Region. First, we hypothesised that pubescence is a xeromorphic trait that conserves water by increasing the boundary layer resistance to diffusion. Water loss was measured in two morphotypes of Leucospermum conocarpodendron (L.) Buek that differ in the degree of leaf pubescence, using both gas exchange and gravimetric techniques. Pubescence contributed less than 5% of total leaf resistance and pubescent leaves transpired at least as rapidly as glabrous leaves due to having larger numbers of small stomata per leaf area. Although pubescence was not associated with drier sites in L. conocarpodendron, there was a weak negative correlation between rainfall and pubescence across 18 other Proteaceae species. We also hypothesised that pubescence is a radiation-protective trait. We assessed the effect of pubescence on light reflectance, leaf temperature, fluorescence and gas exchange characteristics in situ. Pubescent leaves of L. conocarpodendron were 19.2 ± 0.08% more reflective than glabrous leaves and had significantly greater pre-dawn photochemical efficiency. There was a positive association between leaf pubescence and habitat temperature in Proteaceae. We conclude that although pubescence is unlikely to be a xeric adaptation, it could serve a role in reducing photoinhibition and heat loading in Proteaceae species.
Low foristic richness of afro‐alpine vegetation of Mount Kenya is related to its small area
(Springer, 2019-10-29) Nyaga, Justine M.; Onipchenko, Vladimir G.; Kopylova, Natalia A.; Kipkeev, Alii M.; Elumeeva, Tatiana G.; Azovsky, Andrei; Dudov, Sergei V.
Diversity patterns of tropical alpine vegetation is poorly studied. We estimated vascular plant floristic richness for two typical afro-alpine communities in Mount Kenya using a series of nested plots sized from 25 to 100 m2. The α-diversity was low for all plot sizes (4.8–7.8 and 12.8 species per one and 100 m2, respectively). Comparative analysis of α-, β- and γ-diversity across 22 plant communities from five Mountain regions (Mount Kenya, European Alps, Caucasus, Tibet, New Zealand Alps) revealed that area of mountain system was the only significant variable shaping the local richness; this effect became stronger with increasing spatial scale. Beta-diversity, by contrast, showed neither latitudinal trends nor significant correlation with other geographical or climatic variables. We conclude that the total area of mountain system is one of the main factors determining the regional species pool and, ultimately, the local diversity of alpine plant communities (the “echo-effect”). Small area and isolation of Mt. Kenya are considered as the main reasons for low local richness of its afro-alpine vegetation.
Nutritional contribution of atmospheric deposition to the Strandveld vegetation of West Coast South Africa
(University of Cape Town, 2013-07) Nyaga, Justine M.
Ecosystem nutrient availability depends on the balance between rates of nutrient inputs and losses. Nutrients may be lost through fire and displacement of ash, herbivory, leaching and volatilization. The main pathways through which nutrients may be acquired are weathering of rock and atmospheric deposition. Symbiotic and free-living diazotrophic bacteria and blue green algae also contribute N. In ecosystems with limited occurrence of N2-fixation and occurring on low-nutrient bedrock, atmospheric deposition is the most significant source of nutrients. Nutrients from atmospheric deposition may be of natural or anthropogenic origin, and can be “wet-deposited” dissolved in precipitation and “dry-deposited” when aerosols settle out of the atmosphere onto plant and soil surfaces. Studies on nutrient cycling around the world suggest that nutrient deposition can provide substantial amounts of nutrients to coastal ecosystems, although mineral weathering of rocks can also a significant source. Limited prior work on deposition in coastal areas of South Africa suggests that nutrient deposition could be an important component of nutrient budgets in the Cape Floristic Region. The west coast of South Africa borders a section of the Atlantic Ocean that is highly productive and characterized by strong seasonal winds, rough waters and strong wave action. This area is home to the Strandveld vegetation, which grows on marine-derived soils. Based on this, I hypothesized that marine aerosol deposition is a significant source of nutrients for the vegetation in west coast South Africa. To test this hypothesis, I examined the spatial and temporal characteristics of atmospheric deposition as well as the climatic and ecological characteristics of the area. I measured deposition rates and concentrations of essential plant nutrients (N, P, Na, Ca, Mg, and K) delivered in rain University of Cape Town v and horizontal precipitation. Horizontal precipitation was used to refer to all forms of precipitation deposited horizontally and included fog, windblown aerosols, and horizontal rainfall. I then estimated annual demand for these nutrients in 8 plant species growing in the area and compared them to the deposition rates measured in rain. I also compared nutrients deposited in rain water with those deposited in horizontal precipitation, measured the amounts of NO3 -, NH4 + and PO4 3- held in canopies of the 8 plant species during summer, and estimated the species’ capacity for foliar nutrient uptake. The Strandveld vegetation was found to have relatively high soil and plant nutrient concentrations compared to the rest of the CFR, despite its soils originating as nutrient-poor marine derived aeolian sands. Although N and P fluxes deposited in rain were lower than those measured in other pristine sites around the world, a large proportion of TN (84%) and TP (51%) was organic, pointing to a strong marine influence. The marine origin of N and P is supported by the high base cation fluxes compared to those reported globally. The high proportion of organic N and P, and the high base cation contents was also observed in horizontal precipitation. In this form of deposition, base cation concentrations were highest at the coast and contents declined with distance from the ocean, further supporting a possible marine source. This study also suggests that dust may be an important contributor to the deposition of some nutrients during the winter months, and both marine and terrestrial areas could therefore be important sources of nutrient deposition to this area. Based on leaf litter nutrient losses it was estimated that atmospheric deposition through rain alone could potentially supply 36% and 64% of N and P annual demand, respectively, and over 100% of the annual demand for K and Ca. This University of Cape Town vi suggests a strong marine influence in the supply of these nutrients to the Strandveld soils and vegetation. In addition, plants within the Strandveld vegetation intercepted substantial amounts of moisture and nutrients in their canopies. Species with small leaves intercepted significantly greater quantities of water and nutrients than those with larger leaves. It was also established that all the studied Strandveld plants could take up NO3 –, NH4 +, glycine (as a form of organic N) and Li (a proxy for K) through their leaves. Taken together, these results show that the Strandveld ecosystem of West Coast National Park receives substantial inputs of nutrients from marine aerosols, both in rain and horizontal precipitation. This deposition appears to be a critical source of nutrients in an ecosystem with limited bedrock nutrient supplies. Over the time scale of ecosystem development, atmospheric nutrient deposition combined with other ecological characteristics, such as strong moisture-laden winds, may help explain the unique biogeochemical and biogeographical characteristics of the Strandveld.
Precision Agriculture for Resource Use Efficiency in Smallholder Farming Systems in Sub-Saharan Africa: A Systematic Review
(MDPI, 2021-01-21) Nyaga, Justine M.; Onyango, Cecilia M.; Wetterlind, Johanna; Söderström, Mats; Piikki, Kristin
Opportunities exist for adoption of precision agriculture technologies in all parts of the world. The form of precision agriculture may vary from region to region depending on technologies available, knowledge levels and mindsets. The current review examined research articles in the English language on precision agriculture practices for increased productivity among smallholder farmers in Sub-Saharan Africa. A total of 7715 articles were retrieved and after screening 128 were reviewed. The results indicate that a number of precision agriculture technologies have been tested under SSA conditions and show promising results. The most promising precision agriculture technologies identified were the use of soil and plant sensors for nutrient and water management, as well as use of satellite imagery, GIS and crop-soil simulation models for site-specific management. These technologies have been shown to be crucial in attainment of appropriate management strategies in terms of efficiency and effectiveness of resource use in SSA. These technologies are important in supporting sustainable agricultural development. Most of these technologies are, however, at the experimental stage, with only South Africa having applied them mainly in large-scale commercial farms. It is concluded that increased precision in input and management practices among SSA smallholder farmers can significantly improve productivity even without extra use of inputs.
Precision agriculture research in sub‑Saharan Africa countries a systematic map
(Springer, 2021-01-15) Nyaga, Justine M.; Onyango, Cecilia M.; Wetterlind, Johanna; Söderström, Mats
Precision agriculture (PA) has a huge potential for growth in sub-Saharan Africa (SSA), but it faces a number of social-economic and technological challenges. This study sought to map existing PA research and application in SSA countries following the methodology for systematic mapping in environmental sciences. After screening for relevance, the initial about 7715 articles was reduced to 128. Results show that most of the studies were conducted in countries with socio-economic and technological advancement, mainly South Africa followed by Nigeria and Kenya. The studies were conducted at various scales ranging from field to country level with field scale studies being the most common. Most studies were conducted in relatively small farms typical of most farmlands in SSA. Studies done in relatively large farms are fewer, and such farms would likely belong to a few organisations and individuals with high economic capacity. Many of these studies have been conducted by researchers from outside SSA and a combination of researchers from within and outside SSA. However, based on authorship of the articles, it appears that most of the studies conducted in SSA on precision agriculture have either involved or depended on non-African researchers. It is concluded that there have been significant strides towards use of precision agriculture in SSA. However, with about 21 countries having no research done, there exists greater potential for precision agriculture in the region. Besides, there is need for more research to investigate the low usage of precision agriculture for livestock management.
Response of Selected Kenyan Rice Cultivars to Infection by Root Knot Nematode (Meloidogyne incognita)
(Springer, 2019-03-22) Nyaga, Justine M.; Namu, John; Alakonya, Amos; Karuri, Hannah; Masanga, Joel; Njeri, Editah
Meloidogyne incognita causes huge yield losses in rice which is the third most important cereal crop in Kenya. The aim of this study was to identify M. incognita-resistant rice cultivars from Kenya and relate the responses to known resistance pathways with OsPR1a, OsPAL1, and OsJAMYB as marker genes in rice. Five rice cultivars BW 196, Basmati 217 (Pishori), Sindano, IR 2793-80-1 (grown in lowland irrigated fields), and NERICA 4 (grown in upland rainfed fields) were evaluated for resistance to M. incognita under greenhouse conditions in two separate trials. The number of nematode eggs, reproduction factor (RF), and the level of galling were determined. The RF was used to select resistant cultivars. There was a significant difference (P < 0.001) in the number of eggs, galling index, and RF among the cultivars. NERICA 4, BW 196, and Sindano were classified as resistant with an RF <1. There was differential expression of the three marker genes between susceptible and resistant cultivars. OsJAMYB gene was up-regulated in leaves of all rice cultivars after 1 and 3 days post inoculation (dpi). OsPAL1 was up-regulated in leaves of all varieties at 3 dpi while OsPR1a was down-regulated in leaves of resistant plants at 1 dpi and 3 dpi. These results provide an insight on sources of M. incognita resistance in Kenyan rice and it also forms an interesting starting point for further studies on defense responses of common rice varieties to root knot nematode infection.v
SPEI-based spatial and temporal evaluation of drought in Somalia
(Elsevier, 2020-09-06) Nyaga, Justine M.; Musei, Sylus Kipngeno; Dubow, Abdi Zeila
Somalia is one of the most drought prone countries both in Africa and globally. Drought events usually develop gradually unnoticed, causing tremendous effects on both agriculture and environment. This study evaluated the spatio-temporal variations of drought occurrences in Somalia for the period between 1980 and 2015 as quantified by Standardized Precipitation Evapotranspiration Index (SPEI). The intensities, frequencies and trends of drought occurrences were analyzed using SPEI for the multiple timescales of 1-, 3-, 6-, 12-, and 24-month. The temporal variations in drought showed decreasing trends in severity and increasing trends in drought duration as the SPEI timescales increases. The major drought event as identified by SPEI 12 occurred during the period between May 2011 and January 2013 lasting for a period of 12 months with an intensity of 􀀀 0.55. Furthermore, drought count was generally high in the southern parts of Somalia and entire country had suffered droughts ranging from moderately dry to severely dry conditions. An average drought duration of between 2 and 3 months was recorded for most (81%) of the locations. The results of this study could be used to support the water resources management, and to promote the realization of environmental protection and crop production in future.
Temporal variation in physico-chemical characteristics, phytoplankton composition and biomass in Lake Solai, Kenya
(2019-10-20) Nyaga, Justine M.; Koskei, Eunice C.; Kotut, Kiplagat; Oduor, Steve Omondi
The physico-chemical properties and phytoplankton community structure of Lake Solai were investigated between April 2018 and August 2018. Water temperature, conductivity (EC), dissolved oxygen (DO) content and pH were measured in-situ. Nutrient content and phytoplankton biomass were determined in the laboratory. All the water properties; temperature (mean: 23.19 ± 0.13 °C), DO (mean: 6.35 ± 0.03 mgL-1 ), total suspended solids (TSS) (mean: 220.85 ± 8.11 mg L-1), turbidity (mean: 702.51 ± 9.40 NTU), nitrate nitrogen (NO3-N) (mean: 0.75 ± 0.02 mg L-1) total phosphorus (TP) (mean: 20.57 ± 0.51 mg L-1) showed significant temporal variation (P<0.001). Five groups of phytoplankton were identified; Cyanobacteria, was the most dominant with 14 species, Chlorophyta (11 species), Bacillariophyta (8 species), Euglenophyta (3 Species) and Chrysophyta (2 species). The high TP concentration makes it a eutrophic system. The high turbidity create a poor light climate that select against a number of biota that could inhabit the lake allowing for few algal organisms, especially the Cyanobacteria that have the potential to exploit this niche and establish potentially harmful algal blooms. The DO levels were within the permissible limits recommended for fisheries and aquatic life. Hence, the possibility of introducing salt tolerant fish should be explored.
Value chain and sustainability of mangrove wood harvesting in Lamu, Kenya
(Elsevier, 2022-08) Riungu, Purity M.; Nyaga, Justine M.; Githaiga, Michael N.; Kairo, James G.
Mangrove forests provide harvestable wood and non-wood resources to human society globally. The current study evaluated value chain of mangrove wood products from Lamu, Kenya, and how these impacts on resources’ sustainability. Results show that, exploitation of mangrove wood products in Kenya involves several actors, including national regulator, licensees, cutters, transporters, stockists and the consumers. Based on the differences between allowable and harvest data, Lamu mangroves can be said to be under-exploited. For the 1992–2018 period, an average of 223.5 scores ha of mangrove poles were target for harvesting from Lamu. During the same period, the harvest data indicate an average of 6.2 scores ha 1 1 yr of mangrove poles were removed. However, based on stand level data generated as part of this study, mangroves in Lamu are over- exploited and stocked with non-merchantable poles. There are differentiated net income among various actors in mangrove trade in Kenya. Mangrove cutters are among the ‘losers’ in mangrove trade value chain earning a monthly net income of USD118.6 ± 17.9. Winners in mangrove trade is the Kenya Forest Service, Licensees, transporters, and mangrove dealers (or stockists) in urban centers. The findings of this study are critical in development of the harvesting plan for Lamu mangroves. The results will provide insights toward streamlining mangrove trade for community development, revenue generation and environmental sustainability.
Vertical Distribution of Plant-Parasitic Nematodes in Sweet Potato
(Sciendo., 2022) Kemboi, Bernard; Karuri, Hannah; Nyaga, Justine M.; Kingsbury, Aaron J.
Plant-parasitic nematodes (PPN) are harmful pests that have become a severe threat to crop production worldwide. Diversity of PPN at horizontal and spatial scales influence the effectiveness of control strategies. This study evaluated the vertical distribution of PPN genera at 0 cm to 30 cm and 30 cm to 60 cm in sweet potato fields in Central, Manyatta, and Nembure regions of Embu County, Kenya. A significant region × depth interaction was observed for Tylenchus. For all the other nematode genera, there were no significant variations in the abundance at 0 cm to 30 cm and 30 cm to 60 cm depths. However, Helicotylenchus, Meloidogyne, and Scutellonema occurred in greater numbers at both depths in all regions. Shannon and Simpson diversity indices were higher at 0 cm to 30 cm depth while Pielou’s evenness was similar at both depths in the three regions. Diversity partitioning of genus richness, Shannon, and Simpson diversities across all regions at 0 cm to 30 cm, indicated that β component contributed 61.9%, 35.6%, and 22.6% of γ diversity, respectively. Coinertia analysis indicated a significant covariation between nematode genera and soil properties. The results show that management of PPN in sweet potato fields should be targeted at soil depths that are not less than 60 cm.

Browsing by Author "Nyaga, Justine M."

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