Department of Soil Science

Drivers of Gully Erosion and its Socio- economic and Environmental Effects in a Tropical Semi-arid Environment

2026-03-27T13:20:24Z

Drivers of Gully Erosion and its Socio- economic and Environmental Effects in a Tropical Semi-arid Environment Churu, Harrison; Kamau, Solomon; Ng’etich, Wilson; Magiroi, Keziah; Alkamoi, Bonface; Kebeney, Syphyline; Wamalwa, Fred; Mumo, James Gully erosion is a form of severe land degradation, which is more pronounced in semi-arid and arid environments due to their vulnerable ecosystems. Establishing the causes and effects of gully erosion is therefore fundamental in policy formulation and resource allocation for up-scaling context-specific gully mitigation and rehabilitation measures. Thus, this study aimed at assessing the causes and effects of gully erosion in semi-arid region, in the North-West part of Kenya. A cross-sectional survey, field measurements, laboratory analysis, focus group discussions and key informants’ interviews were used to collect data on drivers and effects of gully erosion. Descriptive statistics and content analysis were used to analyze the data. From the findings, 60 % of the respondents reported deforestation as the main driver of gully erosion. Further, 37 and 34 % of the respondents reported surface runoff and steep slopes, respectively, as major drivers of gully erosion. Soils in the region had a high dispersion ratio, with values of between 0.3 and 0.9, making them highly erodible. About 66 and 55 % of the respondents reported that the major effects of gully erosion were reduction in arable land size and death of livestock due to fatal falls, respectively. Approximately 14 ha of arable land and 1,483,600 Mg of sediment have been lost to gully erosion at the rate of about 2,410 Mg ha-1 over a period of 45 years. The average growth rate and density of gullies in the study site stood at 154 Mg ha-1 yr-1 and 0.7 km km-2, respectively. Four people and about 100 cattle had died due to fatal falls into the deep gullies. Thus, there is an urgent need to rehabilitate existing gullies while mitigating occurrence of new gullies in the study area. This would convert existing badlands into hotspots of biodiversity.

Enhancing Sorghum Productivity in Acidic Soils Through Lime– Fertilizer Synergism: Agronomic, Economic, and Composite Performance Analysis

2026-03-26T12:24:41Z

Enhancing Sorghum Productivity in Acidic Soils Through Lime– Fertilizer Synergism: Agronomic, Economic, and Composite Performance Analysis Rotich, Edwin Kiprono; Oloo, Peter Kisinyo; Opala, Peter Asbon; Odundo, Gudu Samwel Sorghum productivity in Western Kenya is severely constrained by acidic soils, particularly Ferralsols and Acrisols prone to aluminum toxicity and phosphorus fixation. This study assessed the performance of limeintegrated fertilizer treatments under smallholder conditions using a randomized complete block design across three sites. Sorghum grain yield (SGY), agronomic efficiency (AE), nutrient uptake efficiency (NUE), and gross margin (GM) were measured alongside the formulation of a composite Performance Index (PI) designed to simulate both physiological and economic effects. We developed a composite Performance Index to integrate agronomic and economic outcomes, enabling balanced evaluation of lime–fertilizer strategies across acid-prone sites. The PI incorporated weighting scenarios reflecting equal and smallholder-adjusted preferences. Results showed that lime enhanced AE (up to 55%), NUE (up to 34.6%), and SGY ≥ 1.8 t ha⁻¹ across sites, with intermediate fertilizer rates yielding superior performance. GM exceeding $450 ha⁻¹ and benefit–cost ratios over 2.0, demonstrating strong economic viability, Lime + N37.5P13 consistently outperformed other treatments, offering agronomic–economic balance and robust PI ranking across sensitivity models. Radar and contour plots identified optimal combinations and revealed trade-offs between efficiency and yield. These findings support lime as a foundational input rather than a supplemental one, and advocate for context-driven ISFM strategies aligned with smallholder realities. The PI framework offers a flexible and empirically grounded tool for sustainable intensification decisions in acid soil systems.

Soil-Plant Nutrient Dynamics and Fertilizer Use Efficiency in Maize & Desmodium Cropping System

2026-03-17T09:18:05Z

Soil-Plant Nutrient Dynamics and Fertilizer Use Efficiency in Maize & Desmodium Cropping System Odera, Irine Akinyi; Otinga, Abigael Nekesa; Njoroge, Ruth; Mutua, Scholastica Soil fertility decline and inefficient nutrient use remain major challenges limiting maize productivity in the arid and semi-arid lands (ASALs) of Kenya. This study evaluated the effects of integrating farmyard manure (FYM) with inorganic fertilizers on soil properties, nutrient uptake, yield performance, and efficiency indices in sole maize sole desmodium and maize-desmodium intercrop systems under field conditions in Keiyo North. The experiment consisted of six fertilizer substitution ratios (0-0, 25-75, 50-50, 75-25, 100-0, and 0-100% farmyard manure-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 combined farmyard manure – 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. Farmyard manure -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. The findings underscore that partial substitution of inorganic fertilizers with farmyard manure, coupled with maize-desmodium intercropping, offers a sustainable pathway to enhance soil fertility, nutrient use efficiency, and productivity in arid and semi-arid lands farming systems.

Nutrient dynamics and decomposition of agroforestry litter in acidic soils of Uasin Gishu County, Kenya

2026-03-13T12:02:22Z

Nutrient dynamics and decomposition of agroforestry litter in acidic soils of Uasin Gishu County, Kenya Nyuma, Henry; Njoroge, Ruth; Otinga, Abigael Multiple forms of biomass, including litter, herbaceous, and woody biomass emanating from agroforestry systems, have numerous environmental and socioeconomic benefits, including improved soil health, biodiversity, carbon sequestration, and diversified income. These benefits are crucial to sustainable production. Despite agroforestry's significant contribution to sustainable food production, less attention is given to litter mass decomposition and its mechanisms of nutrient release and cycling. A study to assess the influence of agroforestry litter quality on decomposition and nutrient release in acidic soils of Uasin Gishu County, Kenya, was conducted at the University of Eldoret. The hypothesis was that the litter type of three agroforestry species - Gliricidia, Leucaena, and Sesbania - affects the rate of decomposition, nutrient release pattern, and the chemical characteristics of acidic soils. Results from the study revealed a significant (P≤0.05) influence of agroforestry litter type and initial litter quality on the rate of decomposition and nutrient dynamics in the order of Sesbania > Gliricidia > Leucaena. Sesbania showed superior litter quality, recording the highest OC (48.1%), N (25.9 g kg-1 ), and Cu (0.35 ppm), and the lowest concentration of lignin (18.0%), cellulose (24.0%), and the lowest C:N, L:N, L:PP, L:P:N, and L:N:P ratios, hence the highest rate of decomposition (k=0.04). Nutrient release was in the order of Fe=Cu>K>Ca>Mg=Mn>N=Zn>P for Gliricidia, Ca>Cu>K=Mn>P>Zn>N for Leucaena, and Ca>Cu>Mn=Mg>P=K>N>Zn for Sesbania. Although there were no significant differences in nutrients released from the three litter types, Sesbania recorded the fastest release of N, P, Cu, and Mn, contributing about 3.2% SOC, 25.5 kg P ha-1 , and 11.4 kg K ha-1 to the soil. Mean soil enrichment (ER=1.1, 1.5, and 2.5) for SOC, P, and K, respectively, indicates the potential of agroforestry litter mass of Sesbania sesban in nutrient cycling. These findings provide insights into the crucial role of agroforestry litter in the cycling of macro and micronutrients, hence enhancing soil ecosystems and sustainable production. However, further studies involving different litter types in multiple agroecological zones are needed to assess the impacts of other environmental factors on nutrient release mechanisms in acid soils.

Response of Rice Beans (Vigna umbellata) to Different Phosphate Fertilizer Rates, Sources and Cropping Systems Established in Western Kenya

2026-03-13T08:51:27Z

Response of Rice Beans (Vigna umbellata) to Different Phosphate Fertilizer Rates, Sources and Cropping Systems Established in Western Kenya Migaya, Erick Omondi; Njoroge, Ruth; Otinga, Abigael N.; Kisinyo, Peter Oloo Rice bean despite being an underutilized crop is a multipurpose legume crop with a potential of improving food security in western Kenya. Acidic soils with low phosphate and organic carbon levels limit its production. We investigated effects of four phosphate fertilizer levels and cropping systems on soils, agronomy and yield components of rice beans in Kaimosi Friends University College (KAFUCO), Rongo University and Siaya Agricultural Training Centre (ATC) farms in Vihiga, Migori, and Siaya Counties in western Kenya in the short rains of 2020 and long rains of 2021. The experiment consisted of twelve treatments replicated three times per site in a split-plot in a randomized complete block design (RCBD). The main plots comprised of three cropping systems(monocrop, conventional and MBILI (Managing Beneficial Interactions in Legume Intercrops)) while the subplots were made up of four phosphate fertilizer levels (without fertilizer (control), inorganic fertilizer (26P+22N kg ha-1 ), pure organic (5P+22N kg ha-1 ) and combined organic and inorganic fertilizers at half rates (15.5P+22N kg ha-1 ). Soil analysis demonstrated that the soils had low P and % organic carbon in all the sites. There were no significant differences in Olsen P at p = .05 in all the sites. In Kaimosi, the average number of pods produced per plant was highest in the mono cropping systems (90) for treatments with mixed organic and inorganic phosphate fertilizers. Treatments with required phosphate fertilizers had the least number of days to flowering (about 75). However, days to 75% flowering in both seasons showed no significant differences in Kaimosi University and Siaya ATC farms with significant differences exhibited in Rongo University farm between the cropping systems at p= .05. The highest average rice beans yields were recorded in Rongo university farm (1.8 ton ha-1 ) for the treatments with mixed organic and inorganic fertilizers in the mono cropping systems. The phosphorus agronomic efficiency was highest in treatments with pure organic matter. The partial factor productivity of phosphorus was highest in the mono cropping systems. There were significant differences in harvest indices, partial factor productivity and phosphorus agronomic efficiency in all the three sites 1.8 ton ha-1 . The study therefore has recommended that phosphate fertilizers are important in the rice beans production for improved yields to be realized.

Aerobic Composting of Antibioticcontaminated Manure: Degradation Processes and Their Effects on Greenhouse Gas Emissions

2026-03-13T08:24:52Z

Aerobic Composting of Antibioticcontaminated Manure: Degradation Processes and Their Effects on Greenhouse Gas Emissions Arusey, Chebet; Kebeney, Syphyline; Ngetich, Wilson Introduction:The widespread use of antibiotics in livestock production results in significant excretion of unmetabolized residues in manure, posing risks such as the emergence of antibiotic-resistant bacteria(ARB), antibiotic resistance genes (ARGs), and elevated greenhouse gas (GHG) emissions. Composting has emerged as a promising strategy to mitigate these risks.Aims:This review formed a foundation for manure incubation regarding the fate and effects of three antibiotics –Tylosin, Enrofloxacin, and Oxytetracycline on manure GHG ammonia (NH3)missions, and fertilizer quality. It synthesizes existing evidence on antibiotic degradation during composting, highlighting the influence of composting conditions,additives,and their effects on greenhouse gas emissions. Methods:A comprehensive literature search was done following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Systematic searches were performed in threedatabases: Web of Science, PubMed, and Scopus, for original articles using a combination of Query terms and an established inclusion and exclusion criteria.Results:The 66 studies that met the criteria were from 21 countries. Outcomes show that composting conditions (temperature, aeration, moisture), additive types (e.g., biochar, zeolite), and microbial inoculants play critical roles in antibiotic degradation and GHG emission dynamics. Thermophilic composting promotes degradation of labile antibiotics, while persistent compounds may require extended treatment. Overall, the review identified that physicochemical and microbial processes drive antibiotic degradation, suggesting that specific additives enhance these pathways, influencing GHG emissions. Conclusion:Composting is a viable strategy for managing antibiotic-laden manure and calls for further research into advanced treatments, bioaugmentation, and integration with other waste management technologies.

Arbuscular Mycorrhizal Fungi Enhance P Uptake and Use Efficiency of Wheat (Triticum aestivum L.) in Ferralsols: A Study at Uasin Gishu County, Kenya

2026-02-17T08:36:39Z

Arbuscular Mycorrhizal Fungi Enhance P Uptake and Use Efficiency of Wheat (Triticum aestivum L.) in Ferralsols: A Study at Uasin Gishu County, Kenya Njoki, Anne; Njoroge, Ruth; Ndungu-Magiroi, Keziah; Kamau, Solomon; Churu, Harrison Deficiency of macro and micronutrients is a major challenge to sustainable wheat production. Integrating biostimulants such as Arbuscular Mycorrhizal Fungi (AMF) and inorganic fertilisers has been shown to enhance wheat production by optimising their mutual benefits. However, integration of AMF and micronutrients has not been prioritised, especially in low-input systems. Thus, a twoseason field study was conducted at the University of Eldoret farm, Uasin Gishu County, Kenya, to evaluate the integrated effect of AMF concoctions with phosphorus (P) and copper (Cu) fertilisers on nutrient uptake, use efficiency, and productivity in wheat. The different levels of P, Cu, and AMF were combined. The treatments were laid out in a Randomised Complete Block Design (RCBD) and replicated three times. Two levels of AMF (0 and 60 L 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: 0 kg, 5 kg, and 10 kg ha-1 . Generalised linear models (GLM) were used to test the effects of AMF and fertiliser type on soil chemical properties and crop performance indices. Two- and three-way interactions between the three factors were also tested. Results show that AMF did not have significant impact on soil available P, while 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 increased P and Cu use efficiency 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 L 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 P fertilisers while increasing wheat grain yield. This study recommends co-application of 60 L AMF and 8.8 kg P ha-1 for improving P nutrition and grain yield in wheat.

POTATO (Solanum tuberosum L.) TUBER YIELD AND QUALITY AS INFLUENCED BY POTASSIUM FERTILIZER IN UASIN GISHU COUNTY, KENYA

2025-05-22T08:33:30Z

POTATO (Solanum tuberosum L.) TUBER YIELD AND QUALITY AS INFLUENCED BY POTASSIUM FERTILIZER IN UASIN GISHU COUNTY, KENYA OKETCH, ANTHONY OTIENO Irish potato is the second most important food crop after maize in Kenya. However, the national average tuber yield is 9.8 tonnes ha-1 which is low compared to optimum production of 41 tonnes ha-1 . There is unmet production demand for potato tubers with high processing quality in Kenya, which can meet international standards for products such as chips and crisps. Potassium (K) is one of the macronutrients taken up in larger amounts by potato and is known to enhance both its yield and quality traits. However, researchers have not reached a consensus on whether K should be applied in Kenyan farms. To determine the effectiveness of potassium fertilizer on tuber yield and quality enhancement as well as profitability due to the fertilizer application, a field experiment was conducted at University of Eldoret farm in Uasin-Gishu County during the short and long rains seasons of 2020 and 2021 respectively. Two sources of potassium, muriate of potash (MOP) and sulphate of potash (SOP) were used at rates of 0, 60, 120, 180 and 240 kg ha-1 of K during the short rains and 0, 30, 60, 90, 120 and 180 kg ha-1 of K during the long rains. Treatments were laid out in a Randomized Complete Block Design replicated three times in a 2x5 factorial during the short rain and 2x6 factorial during the long rain season. Destiny variety of potato was planted. The rate of 120 kg ha-1 of K as sulphate of potash increased marketable tuber yield by 51% relative to the control in the short rains. In the long rains, 30kg ha-1 of K as muriate of potash gave tuber yield of 40.54 tonnes ha1 and profit of 111.86%. SOP significantly enhanced tuber dry matter compared to MOP by 5.6% in both seasons. Further, 180 kg ha-1 of K in form of SOP gave the highest tuber concentration of vitamin C (19.56 mg g -1 ) but similar MOP rate reduced vitamin C content by 5.89 mg g-1 compared to control during long rains. In the short rains, 120kg K/ha gave the highest tuber starch content while similar rate of SOP recorded 4.77% lower tuber starch content. The highest rate of MOP (240kg K/ha) significantly lowered the tuber starch content compared to control. It was concluded that in areas with similar ecological conditions as the study area, tuber dry matter content can be increased by application of sulphate of potash and potato farmers can optimize on their profits and tuber content of vitamin C by application of 30kg/ha of K as MOP and 180kg/ha K as SOP respectively during the long rain season. It is recommended that a similar study be done in different soils where potato is grown and with different varieties.

Findings from a survey in Western Kenya to determine the soil fertility replenishment technologies adoption rates

2025-04-23T07:45:56Z

Findings from a survey in Western Kenya to determine the soil fertility replenishment technologies adoption rates Mong’are, Peris Oroko; et. al... A survey on adoption levels of the existing soil nitrogen replenishing technologies amongst farmers in three counties in western Kenya was carried out in June 2011. Three farmer associations were Angurai Farmers Development Project (AFDEP), Bungoma Small-Scale Farmers Forum (BUSSFFO) and Mwangaza Farmer Group (MFAGRO). During the survey 223 farmers were interviewed with roughly a half of the households surveyed being members of farmer associations (FAs) and the other half being non-members, who acted as the control. Stratified random sampling technique was used. A repeated measures Analysis of Variance (RM – ANOVA) showed that various soil nitrogen replenishment technologies were adopted to various degrees, F (4.39, 855.43) =23.36, p<.001). The findings of this study indicated that the available technologies most extensively used in the study area were the use of inorganic fertilisers (DAP), planting of improved legumes processing, Lab lab, Push Pull, and Super 2 Package. In second place, were technologies such as seed inoculation, foliar feed use, top dressing fertiliser (CAN) and use of improved legumes. The least used technologies were found to be Ua Kayongo (IR seed), MBILI intercropping, fortified compost, and use of Farm yard manure and liming. The results also indicated that generally, adoption of technologies was higher amongst farmer association members compared with non-members regardless of the county. Bungoma County had significantly highest level of technology adoption level compared to both Busia and Vihiga. Adoption of soil technologies was also found to be positively correlated with farmers’ educational level but inversely related with their age.

ENHANCING SOIL NITROGEN THROUGH CROP ARRANGEMENTS AND FERTILIZER: A COMPARATIVE ANALYSIS OF MBILI INTERCROPPING AND CONVENTIONAL METHODS FOR SUSTAINABLE MAIZE- SOY BEAN FARMING IN WESTERN KENYA

2025-04-15T05:44:44Z

ENHANCING SOIL NITROGEN THROUGH CROP ARRANGEMENTS AND FERTILIZER: A COMPARATIVE ANALYSIS OF MBILI INTERCROPPING AND CONVENTIONAL METHODS FOR SUSTAINABLE MAIZE- SOY BEAN FARMING IN WESTERN KENYA OROKO, PERIS NYABOKE Low fertility in highly weathered and degraded soils largely accounts for low and unsustainable crop yields in most African countries. Nitrogen (N) is the most deficient among other nutrients because other than being required in large quantities, is and very susceptible to leaching losses. The study assesses soil N replenishment technologies' impact on adoption rates, yields, and economic benefits of maize-soy bean cropping systems in western Kenya. A baseline survey was conducted on adoption levels of the existing soil N replenishment technologies in three farmer associations (FAs) in June 2011. Management of Beneficial Interaction of Legume Intercrops (MBILI), Mono, and conventional cropping systems’ effects was evaluated on soil N content. In conventional cropping system, Maize (IR) was planted at 75 cm row spacing and 30 cm in-row spacing with soy bean seed planted between the maize at 10 cm spacing. Imazapyr Resistant (IR) maize and soy bean were used as the test crops. The experiment was a split-plot design with two factors (cropping systems as the main factor and fertilizer interventions as the sub factor) arranged in a randomized complete block design (RCBD) with three replications. During the short rains of 2011, (Farm yard manure) FYM (0.965% N) was sourced from the University of Eldoret farm. An application of 75 kg N/ha led to 7.8t /ha of manure. In the long rains and short rains in 2012, FYM from the farmers with 0.39%, 0.73%, and 0.85% N in Teso, Vihiga, and Bungoma counties respectively was applied at 75 kg N/ha. The initial soil characterization results showed that soil cation exchange capacity (CEC) was largest in Vihiga (9.88 cmolc/ kg), Bungoma (5.38 cmolc/ kg) but relatively low in Teso (1.78 cmolc/ kg). In 2011, short rains season, soil Nitrate-N levels were significantly the largest in the fourth week after planting (1.95 mg/kg soil). Maize mono, MBILI and soya mono all had significantly larger Nitrate-N than soils in which a conventional cropping system was practiced. However, in 2012 the long rains season, Nitrate-N, was the largest in preseason (2.62 mg/kg) which decreased to 0.56 mg/kg during 4WAP, before rising to 0.74 mg/kg and 1.49 mg/kg during the eighth and twelfth weeks after planting, respectively. Whereas the cropping system had no significant influence on Nitrate-N, the application of FYM 75 kg N/ha produced a significantly (p<0.05) larger soil Nitrate-N level (1.49 mg/kg) compared with Calcium Ammonium Nitrate (CAN) 30 and 75 kg N/ha at all sampling periods and depths. Maize planted with 75 kg N/ha application yielded 2.24 t/ha and 2.25 t/ha maize grain in FYM treatments, which were significantly larger than the 30 kg N/ha (or FYM 30kg N/ha which gave 1.53 t/ha and 1.64 t/ha respectively. Soy bean yields were significantly larger in the monocropping system compared to both MBILI and the conventional intercropping system. The mean Land Equivalent Ratio (LER) values were always > 1.0 for intercropping cropping system. In maize and soy bean, Nitrogen Use Efficiency (NUE) was largest in the mono-cropping system, followed by MBILI, and lastly, in conventional farming. The largest NUE was realized in FYM30N and CAN30N, whereas FYM75N and CAN75N were lower, suggesting increasing the N application reduces its use efficiency. High soil Nitrate-N was positively correlated (r = 0.430) with yields and NUE at 4WAP in 2011. The MBILI cropping system had the largest gross margin (Kshs 46 164/ha). The largest number of soy bean nodules was in FYM regardless of the application rate and lowest in CAN, implying that FYM is more efficacious in nodulation, especially when applied to nutrient-poor soils. From survey result, least used technologies were found to be Ua Kayongo (IR seed), MBILI intercropping, fortified compost, and use of Farm yard manure and liming. This informed the selection of technologies for this study. Findings from this study showed that MBILI cropping system planted at 30 kg N/ha optimizes crop yields, Nitrate-N utilization, nodulation and NUE, and gross margins.