Department of Soil Science

GREENHOUSE GAS EMISSIONS, SOIL PHYSICOCHEMICAL PROPERTIES, AND NUTRIENT USE EFFICIENCY UNDER INORGANIC-ORGANIC FERTILIZER SUBSTITUTIONS IN MAIZE AND DESMODIUM CROPPING SYSTEMS

Wed, 01 Jan 2025 00:00:00 GMT

GREENHOUSE GAS EMISSIONS, SOIL PHYSICOCHEMICAL PROPERTIES, AND NUTRIENT USE EFFICIENCY UNDER INORGANIC-ORGANIC FERTILIZER SUBSTITUTIONS IN MAIZE AND DESMODIUM CROPPING SYSTEMS ODERA, IRINE Climate change continues to threaten ecosystem functions, and agriculture remains one of the major sources of greenhouse gas (GHGs) emissions responsible for global warming. However, little is known about the quantities and intensities of GHGs from major cropping systems in Kenya and, by extension, in Sub-Saharan Africa. This study was aimed to quantify GHG emissions - carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) fluxes from soil. It also assessed the optimal organic-inorganic fertilizer substitution in maize (Zea mays) and desmodium (Desmodium uncinatum) cropping systems that enhance crop yields and lead to reductions in GHG emissions. The static chamber method was used from April to November 2024. The experiment consisted of six fertilizer substitution ratios (0 0, 25 75, 50 50, 75 25, 100 0, and 0 100% FYM-inorganic N equivalence) arranged in a randomized complete block design with four replications. Soil chemical parameters (NH4+, NO3−, pH, N, P, and C), plant nutrient uptake, and agronomic and recovery efficiencies were assessed. Results showed that desmodium yield responded positively to increasing Farmyard manure substitution levels (p < 0.0001), with biomass rising under higher organic inputs. Despite these, N2O emission factors and yield-scaled emissions remained consistently low across fertilizer treatments, indicating efficient nitrogen utilization and minimal gaseous losses. The net global warming potential did not vary significantly among treatments. Greenhouse gas intensity declined sharply from the control to the 75,25 fertilizer treatment, representing approximately a 70% reduction. Maize grain yield was highest under the 50,50 (50% FYM, 50% inorganic fertilizer), indicating a strong synergistic effect between organic and mineral nutrient sources. Emission factors increased by nearly 20% relative to the control. Net global warming potential also increased progressively with higher Farmyard manure substitution, showing an approximately 40.7% increase. Despite these increases, the 50,50 treatment achieved the most favorable balance between productivity and emissions, producing the highest maize yield with comparatively lower EF and greenhouse gas intensity (GHGI). Combined FYM–inorganic treatments, particularly 25,75 and 75,25, significantly improved soil nutrient status, enhanced N and P uptake, and increased maize and desmodium yields compared to sole applications. FYM- rich combinations improved moisture retention and microbial activity, sustaining nutrient release, while inorganic fertilizers ensured rapid early growth. Intercropping enhanced biological nitrogen fixation and nutrient recovery, leading to higher agronomic efficiency and resilience under moisture-limited conditions.

SPATIOTEMPORAL DYNAMICS OF RIPARIAN GREENHOUSE GAS FLUXES AND SOIL CARBON STOCKS IN THE BURA AND WUNDANYI CATCHMENTS, KENYA

Wed, 01 Jan 2025 00:00:00 GMT

SPATIOTEMPORAL DYNAMICS OF RIPARIAN GREENHOUSE GAS FLUXES AND SOIL CARBON STOCKS IN THE BURA AND WUNDANYI CATCHMENTS, KENYA OWUOR, GODFREY Agropastoral riparian zones are globally linked to increased greenhouse gas (GHG) emissions and soil organic carbon (SOC) depletion, but the Kenyan cases are underrepresented in global datasets. The study investigated variations in GHG fluxes and SOC stocks across three livestock production density levels in the Bura and Wundanyi sub- catchments. Eighteen (18) riparian sites (high livestock density (HLD n=7), low livestock density (LLD n=4), and zero density (ZLD n=7) were sampled between 2021 and 2022 in 2 dry seasons and 2 wet seasons in three topographies [(Upland at >1000 masl), (Midland 700 - <1000 masl), and (Lowland <700 masl)]. Results from Wundanyi showed higher CH4 fluxes under HLD, particularly in the midland zones, where emissions reached 302.5 μg CH4 m−2 d−1. In contrast, ZLD sites acted as net CH4 sinks. The mean CH4 flux for Wundanyi was 30.21 mg CH4-C m−2 d−1. Consistently high CO2 fluxes were recorded in Wundanyi with a mean of 900.17 mg CO2-C m−2 d−1. The highest mean was observed at the ZLD sites, Upland (1146.75 mg CO2-C m−2 d−1) and Midland (1003.25 mg CO2-C m−2 d−1). SOC stocks in Wundanyi averaged 6.91 Mg C ha−1, with higher concentrations recorded in Upland areas (8.01 Mg C ha−1). These stocks were greater during wet seasons (8.47 Mg C ha−1) and showed an increasing trend with livestock density: 6.67, 7.03, and 7.40 Mg C ha−1 in ZLD, LLD, and HLD, respectively. In Bura, CH4 fluxes were predominantly negative with mean absorptions in Midland LLD and Upland HLD areas (- 169.27 and -256.63 mg CH4-C m−2 d−1), respectively. CO2 emissions were moderate, with a mean of 527.07 mg CO2-C m−2 d−1, remaining <700 mg CO2-C m−2 d−1 across sites and livestock systems. N2O fluxes in Bura were moderate, peaking at 155.93 μg N2O-N m−2 d−1 in Midland zones under HLD. SOC stocks were highest in the Midlands at 8.29 Mg C ha−1, with values increasing alongside livestock density (7.13, 7.78, and 9.16 Mg C ha−1 for ZLD, LLD, and HLD, respectively. Bura was a strong methane sink, while Wundanyi recorded CH4 emissions in grazed areas and net uptake in ZLD. The upland and ZLD areas were significant CO2 sources. This study confirms that increasing livestock densities depleted SOC stocks with appreciable human disturbance contributions. Livestock production densities are dictated by topography, and GHG emissions are often part of natural exchange processes. To realise sustainability in livestock systems, sustainable stocking densities, protecting riparian strips, and enhancing vegetative cover should be practised. Long-term catchment-level research to document seasonal nutrient input-output dynamics would improve GHG inventories for sub-Saharan Africa.

EFFECT OF PHOSPHORUS FERTILIZER AND CROPPING SYSTEMS ON RICE BEAN (Vigna umbellata, L.) PRODUCTION IN WESTERN KENYA

Wed, 01 Jan 2025 00:00:00 GMT

EFFECT OF PHOSPHORUS FERTILIZER AND CROPPING SYSTEMS ON RICE BEAN (Vigna umbellata, L.) PRODUCTION IN WESTERN KENYA MIGAYA, ERICK Low soil phosphorus (P) remains a critical constraint to sustainable legume production in Western Kenya. Rice bean (Vigna umbellata L.), a resilient and nutrient-rich yet underutilized legume, offers opportunities for food security enhancement and soil fertility restoration. The crop productivity has been hindered by nutrient deficiencies and suboptimal cropping systems. This study evaluated the effect of phosphorus fertilizer and cropping systems on rice bean soil fertility dynamics, phenology and yields across three agroecological sites; Siaya, Rongo and Kaimosi over two consecutive seasons (September– December 2020 and March–August 2021). A split-plot design was used, with cropping system (monocrop, conventional intercrop and MBILI) as the main factor and P amendments (control at 0 kg P ha−1, FYM at 5 kg P ha−1, combined FYM + inorganic at 15.5 kg P ha−1, and sole inorganic at 26 kg P ha−1) as the subplot factor, replicated three times per site. Data on soil available P, phenological stages, pods per plant, grain yields, phosphorus agronomic efficiency (PAE) and harvest index (HI) were collected and analyzed using Analysis of Variance (ANOVA). Results showed that soil available P was highly responsive to P amendments, with 26 kg P ha−1application producing the highest levels (up to 8.88 mg kg−1 at Rongo monocrop), while 15.5 kg P ha−1 application maintained moderately high levels that balanced immediate nutrient supply with long-term fertility. Cropping system effects on soil P were less pronounced, but monocropping and MBILI showed slightly greater retention than conventional intercropping. Phenological responses were notable: 0 kg P ha−1 plots matured 12–17 days later than 15.5 kg P ha−1 or 26 kg P ha−1 treatments, with delayed flowering and extended vegetative growth under P deficiency. Across sites and seasons, grain yields ranged from 0.24 t ha−1 in conventional controls at Siaya to 1.72 t ha−1 under monocrop with 15.5 kg P ha−1 P in Rongo, highlighting the clear yield advantage of combined nutrient management in low-P soils. PAE varied widely, peaking at 63.42 kg kg−1 under monocrop with fertilizer treatment of 15.5 kg P ha−1 at Rongo. The PAE was higher under the fertilizer treatments of 5 kg P ha−1 and 15.5 kg P ha−1 treatments than under 26 kg P ha−1, indicating superior nutrient use efficiency with organic amendments. Harvest index values reflected biomass partitioning, highest in conventional and MBILI systems (up to 11.10%) compared to 3–4% in monocrops. The study concludes that combining organic and inorganic phosphorus sources within site-specific cropping systems accelerates phenological development, improves nutrient use efficiency and maximizes yield in rice bean production. Extension programs should prioritize farmer training on integrated soil fertility management to promote organic–inorganic nutrient combinations. These findings provide a framework for sustainable intensification of underutilized legumes in phosphorus-deficient soils.

Socio-Economic Factors Influencing Solid Waste Management in Urban Centres of Nandi County

Wed, 01 Jan 2025 00:00:00 GMT

Socio-Economic Factors Influencing Solid Waste Management in Urban Centres of Nandi County Meli, James; Sumukwo, Joel; Lagat, Kiplimo Rapid population growth, urbanization, industrialization and economic development have resulted in the generation of big volumes of solid waste in Nandi County. Yet solid waste is an economic commodity that may not be optimally allocated through the market mechanism. Most attempts to solve waste problems in Kenya focus on supply-side of waste disposal and collection, which have not been successful. This study examines the following objectives: Assess the effects of education, age, and gender on management of solid waste; evaluate how household incomes influence SWM in Nandi County; examine various policy options in management of urban solid waste in Nandi County. This study is guided by utility theory which provides a valuable framework for understanding and analyzing decision-making processes related to waste management practices. Data were collected through stratified sampling of 380 respondents, where interview guides and questionnaires were applied. Key findings reveal that gender and income levels are significant predictors of solid waste generation. High-income earners (KSh. 91,000–100,000 monthly) are the largest waste generators, while low-income earners (<KSh. 30,000) cumulatively generate less. Industrial and packaging-related waste accounts for 37% of corporate waste, followed by tea waste (20%) and market waste (15%), reflecting the dominance of manufacturing and agricultural trade in the region. A multiple regression analysis proved that gender, and monthly household income, collectively explained up to 50% of the variation of solid waste management. These results indicate the need for development of gender-specific strategies and policies that are oriented to income disparities, to improve solid waste management. The study recommends offering incentives for minimization of waste disposal such as waste-to-energy practices for tea companies and establishment of affordable recycling facilities for low-income households and informal sector players.

Economic Value of Solid Waste for Improved Solid Waste Management in Nandi County, Kenya

Thu, 01 May 2025 00:00:00 GMT

Economic Value of Solid Waste for Improved Solid Waste Management in Nandi County, Kenya Meli, James; Sumukwo, Joel; Lagat, Kiplimo Due to rapid population growth and urbanization Nandi County is experiencing challenges of managing urban solid waste especially as this is an economic commodity that may not be optimally allocated through the normal market mechanism system. This is because supply-side management practices have failed and hence there is need for demand-oriented approach. The objectives of this study include; assessing the WTP for improved management of solid waste; evaluate potential income opportunities in managing waste; and provide policy implications. The study used a sample size of 380 households through stratified sampling procedures. Interview guides and questionnaires were used in data collection. Results show that only 27% of individual residents and 18% of corporate organizations paid for these services while the rest (73% and 82% respectively) cannot internalize environmental degradation. High income households expressed the highest willingness to pay (WTP) of 60%. On average respondents WTP is Ksh. 300 monthly for improved services, while corporates had WTP of KSh. 1,000. Regression analysis showed that gender, education level, and household income were significant predictors of WTP. The study concluded that gender, education level, and household monthly income significantly influence individuals' willingness to pay for improved solid waste management in Nandi County. It recommends strengthening regulations to enforce proper waste disposal and introduce equitable tariff structures. Expanding participation through affordable rates will help achieve economies of scale, ensuring sustainable financing for waste management services

Influence of pH Variation on Lead Uptake and Accumulation in Raphanus raphanistrum and Brassica napus Grown in Spiked and Limed Agricultural Soils of Moiben Sub-County, Kenya

Fri, 01 Aug 2025 00:00:00 GMT

Influence of pH Variation on Lead Uptake and Accumulation in Raphanus raphanistrum and Brassica napus Grown in Spiked and Limed Agricultural Soils of Moiben Sub-County, Kenya Barno, Faith; Gelas, Simiyu; Mulei, Josephine This study assessed Pb uptake and distribution in Raphanus raphanistrum (RR) and Brassica napus (BN) grown in agricultural soils from Moiben Sub-County, Kenya, under three soil treatments: Pb-spiked soil (to ≈1000 mg/kg), non-spiked soil, and spiked soil amended with lime (to achieve pH≈7.4). Pb concentrations were quantified using Atomic Absorption Spectrophotometry (AAS), and the Bioaccumulation Factor (BAF) was calculated for roots, stems, leaves and seeds. Data were analyzed using SPSS v25. Descriptive statistics (means, standard deviations) were computed for Pb concentrations in soil and plant tissues. One-way ANOVA tested differences among treatments (control, spiked, limed), with Tukey’s HSD applied for post hoc comparisons. Results showed that Raphanus raphanistrum accumulated mean Pb concentrations of 1043.80 ± 18.34 mg/kg in spiked soils, 25.49 ± 0.39 mg/kg in non-spiked soils, and 548.24 ± 17.75 mg/kg in spiked and limed soils. Brassica napus followed a similar trend, with significantly higher Pb accumulation in spiked compared to non-spiked soils, while liming reduced uptake by nearly 50%. In both species, roots exhibited the highest BAF across treatments, while stems consistently recorded the lowest. In spiked soils, the accumulation trend was roots > seeds > leaves > stem, whereas in limed soils it shifted to roots > leaves > seeds > stem, with overall BAF values reduced to <1. Although liming effectively reduced Pb uptake, both Raphanus raphanistrum and Brassica napus accumulated Pb levels in edible parts above FAO/WHO permissible limits (0.3 mg/kg for leafy vegetables, 0.1 mg/kg for root/tuber crops, and 0.2 mg/kg for cereals and oilseeds), raising concerns over food safety. The findings highlight the influence of soil

Assessing Status of Agroecological Biodiversity in Smallholder farming: Evidence from FAO TAPE Tool Localization in Busia County, Kenya

Fri, 01 Aug 2025 00:00:00 GMT

Assessing Status of Agroecological Biodiversity in Smallholder farming: Evidence from FAO TAPE Tool Localization in Busia County, Kenya Kerubo, Suzzette; Otinga, Abigael; Njoroge, Ruth; Ongeri, Lilian; Ambale, Vincent Agroecological biodiversity is the variety and variability of above ground organisms, that is crops, livestock, trees, and activities considered under agricultural systems. This study investigated the extent of above ground agroecological biodiversity among small-scale farmers in Busia County. Agroecological diversity (above ground) was measured using four indicators of the FAO's Tool for Agroecology Performance Evaluation-TAPE: crop, livestock, tree, and activity diversity. Administrative wards were purposively selected where a sample size of 210 was sourced. Households were randomly selected, top 35 households, within those administrative wards. For administrative wards with less than 35 households, snowballing was conducted to reach the required number of households. Snowballing was also conducted to households that were unavailable and to those who did not give consent. Data was collected through structured questionnaires and administered to respondents by trained enumerators. The results revealed that the agroecological biodiversity scores recorded: 40.5%, 31.25%, 45.5%, and 41.75%, for crops, livestock, trees, and activities, respectively, with an overall score of 39.75%. This interprets to unsustainable extent of practice, reflecting missed opportunities to harness agroecological biodiversity. Farmer education and technical extension by up to date standardized trained officers on agroecological biodiversity can be strengthened through mass media, agricultural shows, and farmer school centres. Additionally, promoting practical guidance on integrating locally appropriate species and practices can help unlock the full extent and adoption of agroecological biodiversity.

EFFICIENCY OF ARBUSCULAR MYCORRHIZAL FUNGI IN ENHANCING PHOSPHORUS AND COPPER UTILIZATION IN WHEAT GROWN IN FERRALSOLS OF UASIN GISHU COUNTY, KENYA

Wed, 01 Jan 2025 00:00:00 GMT

EFFICIENCY OF ARBUSCULAR MYCORRHIZAL FUNGI IN ENHANCING PHOSPHORUS AND COPPER UTILIZATION IN WHEAT GROWN IN FERRALSOLS OF UASIN GISHU COUNTY, KENYA Njoki, Anne Declining soil fertility characterized by deficiency of both macro and micronutrients is a major challenge to sustainable wheat production. Integrating bio-stimulants such as Arbuscular Mycorrhizal Fungi (AMF) with inorganic fertilizers has been shown to have the potential to enhance wheat production by optimizing their mutual benefits. However, a combination of AMF and micronutrients has not been given the necessary attention, especially in low-input systems such as those dominant in sub-Saharan Africa. Thus, the current study was conducted in Uasin Gishu County, Kenya, for two seasons to evaluate the effect of integrating AMF with phosphorus (P) and copper (Cu) fertilizers on wheat grain yield, nutrient uptake, and use efficiency. Two levels of AMF (0 and 60 kg ha -1 ) were applied with three levels of P: 0 kg, 8.8 kg, and 17.6 kg ha -1 , and three levels of Cu at 0 kg, 5 kg, and 10 kg ha -1 . The experiment was conducted in an RCBD, and fertilizer treatments were applied in a factorial arrangement in the 2018 and 2019 long rains seasons. Results showed that while AMF did not have a significant impact on soil available P, available Cu increased by 32% - 40% compared to the control. AMF also enhanced P and Cu uptake by 27 - 30% and 24 - 38%, respectively. Furthermore, AMF boosted P and Cu uptake efficiency by 30 - 35% and 25 - 40%, respectively, whereas P and Cu use efficiency increased by about 15 - 31% and 18 - 35% above the plots without AMF, respectively. Co-application of P at 8.8 kg ha -1 and 60 kg AMF ha -1 recorded the highest wheat grain yield of 2.84 and 4.72 Mg ha -1 during the 2018 and 2019 long rain seasons, respectively. The study shows that the use of AMF could play a significant role in reducing the amount of inorganic fertilizers, which cuts down the cost of production to most smallholder farmers, but at the same time enhancing nutrient uptake and use efficiencies, and thus grain yield. This study recommends co-application of 60 kg ha -1 of AMF and 8.8 kg P ha -1 for optimal wheat yield and P nutrition in wheat.

Spatial–Temporal Influence of Sand Dams on Chemical and Microbial Properties of Water from Scooping Holes in Degraded Semi-Arid Regions

Fri, 01 Sep 2023 00:00:00 GMT

Spatial–Temporal Influence of Sand Dams on Chemical and Microbial Properties of Water from Scooping Holes in Degraded Semi-Arid Regions Churu, Harrison; Kamau, Solomon; Ngetich, Wilson; Magiroi, Keziah; Alkamoi, Bonface; Kebeney, Syphyline; Wamalwa, Fred; Mumo, James Communities in semi-arid lands use sand dams to enhance access water during the dry seasons. However, there is limited information on the quality of water derived from these sand dams, especially in degraded lands where storm surface runoff poses contamination risk. Thus, this study aimed at assessing the spatial–temporal variations in water quality of sand dams in Chepareria, West Pokot County in Kenya. Water samples were collected from scooping holes across 18 purposefully selected sand dams. Results obtained showed significant differences in water quality based on a sand dam’s age and location of the scooping holes, but the magnitude of these differences differed with specific properties. For instance, in recently constructed sand dams (<1 year), scooping holes near the sand dam wall had lower pH values (8.5) than holes scooped a distance from the sand dam wall (9.2). For total dissolved solutes and microbial properties, sand dam age had the greatest impact, over the location of the scooping holes. For example, water obtained from <1 year old sand dams had significantly higher TDS with an average value of 100.3 mg L−1 . The thermotolerant coliforms (TTC) exceeded the maximum allowable levels recommended by The World Health Organization. Thus, water obtained from these sand dams should be treated before consumption. Finally, sand dams meant for domestic water harvesting should be protected. Shallow wells with appropriate aprons for effective protection against contamination should be installed to enhance abstraction of safe water from sand dams.

A Review on Challenges and Opportunities in Management of Soils of Arid and Semi-Arid Regions of Kenya

Sat, 01 Jan 2022 00:00:00 GMT

A Review on Challenges and Opportunities in Management of Soils of Arid and Semi-Arid Regions of Kenya Nyuma, Henry Tamba; Churu, Harrison Arid and semi-arid lands occupy currently 88% of arable land mass in Kenya, a region with significant diversity of production systems and economic opportunities. However, these areas are characterised by low and erratic rainfall, hence challenges to agriculture and socioeconomic development in the wake of an increasing population and the impacts of climate change. This review seeks to identify key challenges and opportunities associated with the management of agricultural soils in these arid and semi-arid communities. Arid and semi-arid regions in Kenya are dominated by 10 soil types; Solanchaks, Solonetz, Cambisols, Arenosols, Leptosols, Vertisols, Fluvisols, Phoezems, Calcisols, and Gypsisols. Among the main soil fertility challenges in these soils are moisture stress, high erodibility, and low organic matter content, salinity, and sodium toxicity, the deficiencies of mainly N, P, Zn, and Fe, hence the vulnerability of over 14 million inhabitants to the shocks of low crop and pasture production. Moreover, the adoption of soil conservation practices remains low as existing soil fertility management technologies have been criticized for being too abstract and not providing context and site-specific solutions. Improving soil fertility and moisture levels enhances soil ecosystem functions and food and pasture production in these regions. Encouraging farmers to join soil and water conservation groups, while providing economic incentives, could potentially accelerate the adoption of soil and water practices at the farm level through pulling resources together. Future research to validate a site and context-specific integrated soil fertility improvement technologies for these soils is evitable to enhance soil functions, agricultural production and livelihood at house hold level.