Nitrogen forms in three Kenyan soils Andosols, Lucidols and Ferralsols

The nitrogen cycle in soil is an integral part of the overall cycle of N in nature. The primary source of N is the atmosphere where the strongly bonded gas molecule N is predominately gas (78.08%). Total N content in soils ranges from 0.02% in the subsoil and more than 2.5% in peats; ploughed layers of most cultivated soils contain between 0.06 and 0.5%. The amount present in each case is, however determined by climate, type of vegetation, topography, parent material and activities of man. Over 95% of TN in surface soils is organically bound while the portion of non-exchangeable N is high in subsurface soil. Knowledge concerning the nature of organic N in soils is based on studies involving identification and estimation of N forms released by treatment with hot acids. Organic N forms were determined in three soils by acid hydrolysis. The total hydrolysable organic N for the 0-15 and 15-30 cm layers were 57.2 and 59.3% for Gituamba andosols; 56.9 and 61.9 for Kitale ferralsols; 39.0 and 42.1% for Katumani luvisols, respectively. Amide N ranged from 11.6 to 21.4% of total N; Hexosamine from 5.2 to 10.1% and Amino acid N from 26.2 to 37.1 %. Amino acid N therefore formed the highest portion followed by Amide N of the hydrolysable organic N

Effects of Tillage Practices and Organic Cropping Systems on the Yield of Sorghum (sorghum bicolor L.) and Sweet Potato (Ipomoea batatas L) in Yatta Sub-County, Kenya

The study was conducted between October 2012 to February 2013 short rain season (SRS) and April 2013 to August 2013 long rain season (LRS) in semi-arid Yatta sub-county, to evaluate the influence of tillage practices, cropping systems and organic inputs on the yield of sorghum and sweet potato. A Randomized Complete Block Design with a split-split plot arrangement replicated thrice was used. The main plots were tillage practices (TP); Oxen plough (OP), tied ridges (TR) and furrows and ridges (FR). The Split-plots were cropping systems (CS); mono-cropping (MC), intercropping (IC), and crop rotation (CR) while split-split plots were organic inputs; Farm Yard manure (FYM), Minjingu Rock Phosphate (MRP), combined MRP and FYM (MRP+FYM) and the control. Test crops were sorghum and sweet potatoes with Dolichos (Dolichos lablab) and chickpea (Cicer arietinum L) either as intercrops or in rotation. Plant sampling was done by harvesting the grain and tuber and yield determined by weighing with a precision balance. The yields increased significantly (P≤0.05) with application of MRP+FYM of 16.37 and 1.38 t ha-1 for sweet potatoes and sorghum mono-crop, respectively under TR were observed. There was also significant (P≤0.05) yield increase of chickpea and dolichos under combined TR, IC of sorghum with chickpea (1.44 t ha-1) and dolichos (1.38 t ha-1) and with application of MRP+FYM during SRS of 2012. Improved yield of srghum and sweet potatoes were attained with the combined TR, MC and with application of MRP + FYM

EFFECT OF DIFFERENT COVER CROP RESIDUES, MANAGEMENT PRACTICES ON SOIL MOISTURE CONTENT UNDER A TOMATO CROP (LYCOPERSICON ESCULENTUM)

SUMMARYThe soil water storage, soil water content, available water content and soil water balance under various cover crop residue management practices in a Nitisol were evaluated in a field experiment at the Kabete Field Station, University of Nairobi. The effects of surface mulching, above and below ground biomass and roots only incorporated of (mucuna pruriens), Tanzanian sunnhemp (Crotalaria ochroleuca) and Vetch (Vicia benghalensis) cover crops, fertilizer and non fertilized plots on soil water balance were studied. Tomato (Lycopersicon esculentum) was used as the test crop. Since water content was close to field capacity, the drainage component at 100 cm soil depth was negligible and evapotranspiration was therefore derived from the change in soil moisture storage and precipitation. Residue management showed that above and below ground biomass incorporated optimized the partitioning of the water balance components, increasing moisture storage, leading to increased tomato yields and water use efficiency. Furthermore, vetch above and below ground biomass incorporated significantly improved the quantity and frequency of deep percolation. Soil fertilization (F) and non fertilization (NF) caused the most unfavourable partitioning of water balance, leading to the lowest yield and WUE. Tomato yields ranged from 4.1 in NF to 7.4 Mg ha-1 in Vetch treated plots. Vetch above and belowground biomass incorporated had significant (p ≤ 0.1) yields of 11.4 Mg ha-1 compared to all other residue management systems. Vetch residue treatment had the highest WUE (22.7 kg mm-1 ha-1) followed by mucuna treated plots (20.7 kg mm-1 ha-1) and both were significantly different (p ≤ 0.05) compared to the others irrespective of residue management practices

Effect of water conservation measures on soil moisture and maize yield under drought prone agro-ecological zones in Rwanda

This study was conducted to assess agricultural practices for generating maximum maize productivity in drought prone agro-ecological zones. The experiment was conducted in Cyili sub-catchment in Southern Province of Rwanda, which has an irregular rainfall distribution and a prolonged dry season. The experimental design consisted of a randomized design and each treatment was replicated three times. Findings from this study revealed that maize grain yield and yield components, such as plant height, cob diameter and length, number of leaves, 100 grain weight, and yield per plant were highly significantly affected (P  0.05). Supplementary irrigation treatment increased maize yield production to 11,982 kg ha-1. Mulching increased yield significantly to 8089 kg ha-1. Ridges yielded 5937 kg ha-1, and rainfed treatment yielded 4755 kg ha-1 of maize. Based on Pearson's correlation coefficients, grain yield and yield components were positively correlated and statistically significant (p < 0.001) under various water conservation methods. Supplementary irrigation through rainwater harvesting was found to be a more promising option for maize growers to mitigate dry spell and stabilize maize production in rainfall deficient agro-ecological conditions not only in Rwanda, but in sub-Sahara Africa. Keywords: Maize yield, Mulching, Tied ridges, Supplementary irrigatio

Income mobility in diversified CSA households of Nyando Basin, South Western Kenya

Climate-Smart Agriculture (CSA) strategies have been introduced in the Nyando basin (comprising Kisumu and Kericho Counties) in Kenya, and farmers have comparatively taken up the practices. This has resulted in the diversification of farming crops/livestock and incomes to bridge seasonal shortfalls under erratic harsh weather conditions due to climate change. The main objective of the study was to determine how smallholder farmers bridge seasonal incomes variations. This study demonstrates income diversification probabilities on four outcomes of climate-smart agriculture; agricultural practices, sales of goods and services, gifts/remittances, and savings (deposits/retrievals). Additionally, gender aspects were aggregated on the same in climate-smart villages (CSVs) and non-CSVs communities. The study used household-level financial diaries panel data, collected in 2019/2020 from 124 samples of farmers selected by a multistage sampling technique. Descriptive statistics and a multinomial logistic model were used to determine the risk/probability of income sources and mobility (livelihood diversification) from a set of strategies. Results indicated that agriculture diversification activities (sale of goods and services and agricultural practices) as income sources were seasonal-sensitive and during droughts, households diversified to gifts/ remittances and savings. Education, age and household size were noteworthy aspects that influenced the choice of livelihood diversification strategies there were gender differences in sources of contributions to household transactions whereby women mainly relied on Gifts/Loans/Credit/Advances while sales of goods and services were exhibited in men. CSVs predictors on all the income sources over the year were negative and not significant indicating a greater probability of CSVs shifting incomes sources to sales of goods than the non- CSVs

Formulation of slow release NPK fertilizer (cellulose-graft-poly(acrylamide)/nano-hydroxyapatite/soluble fertilizer) composite and evaluating its N mineralization potential

Polymer nano-composite fertilizer formulation has the potential to enhance nutrient use efficiency. Slow release fertilizer (SRF) composite was formulated by incorporating nano-hydroxyapatite (nano-HA) and water soluble fertilizers (urea, (NH4)2HPO4 and K2SO4) into water hyacinth cellulose-graft-poly(acrylamide) polymer hydrogel. Fourier Transform Infra-red spectra revealed existence of chemical interaction between the monomer, cellulose, urea and nano-HA. The release of nutrients was assessed using laboratory incubation experiment. Significantly higher content of mineral nitrogen (MN) was observed in the first 4 weeks in conventional fertilizer (CF) compared to SRF treatments and the control. MN content in SRF treatments increased considerably between the 8th and 12th week, and declined in the 16th week. The values of potentially mineralizable N estimated using first order kinetics model related well to the observed cumulative MN at 16th week. No significant difference was observed between CF and SRF treatments for available P content in the 2nd week. Significantly higher P content was observed in CF compared to SRF treatment in the 4th week, whereas in the 8th week, some SRFs released significantly higher content than CF. Available P peaked in the 8th week in all the treatments and remained constant at 12th and 16th week. Availability of P in SRFs increased with increased content of soluble P and decreased content of nano-HA. Exchangeable K showed less variation during the incubation period, suggesting short release time. The data revealed reduced chances of leaching losses and toxic effect to the plant roots, as well as synchronized nutrient release and requirement by crops. Keywords: Nano-composite, Polymer hydrogel, Chemical interaction, Incubation experiment, Kinetics mode

ORGANIZATION AND PERFORMANCE OF WATER RESOURCE USERS’ ASSOCIATIONS IN THE SOUTHERN RANGELANDS OF KENYA

Water insecurity is a threat to pastoral livelihoods and sustainability. The Water Act of Kenya, 2002, created the Water Resource Users’ Associations (WRUAs) to enhance water resource conservation access at the local level.  Nevertheless, environmental degradation has increased in recent times, further exacerbating water crisis and threatening livelihoods. This study sought to assess the status of community based water resource conservation in the Southern rangelands of Kiserian, Kajiado County, Kenya. Kiserian WRUA members were purposively sampled for this survey. Data was mainly collected through administration of a semi-structured questionnaire.  Focus group discussions and key informant interviews were also conducted to validate the data obtained from the questionnaire. Chi-square and descriptive statistics were used to analyze the data using SPSS version 20.  Results indicated that access to information on water conservation and training were significantly associated, with membership to the WRUA (χ2=0.56, p≤0.05) and (χ2=0.71, p≤0.05), respectively. Majority (79.5%) of the Kiserian WRUA members had participated in tree planting within the catchment. Half (50%) of the WRUA members were mainly motivated to join the association because of perceived benefits like improved access to water at lower prices and participation in catchment protection. The main challenges facing the WRUA were inadequate funding from the government and other stakeholders (93.2%) and lack of support from county leadership (34.1%). It was concluded that WRUAs, especially in the rangelands of Kajiado, Kenya, played a key role in catchment conservation and water access for resilient livelihoods among pastoralists. This study therefore recommends awareness to increase WRUA membership and allocation of sufficient funding from the government and other related stakeholders to WRUA conservation activities, if catchment conservation for improved water access in the area is to be realized

Modelling surface runoff using the soil conservation service-curve number method in a drought prone agro-ecological zone in Rwanda

Runoff farming is reported to improve land productivity and crop yields in hot and dry climates. This study was conducted to assess the available rainwater that can be harvested in a conserved catchment in a drought prone agro-ecological zone. The study was carried out in the Cyili sub-catchment, southern province of Rwanda, which has an irregular rainfall pattern and unexploited runoff water. Soil Conservation Service-Curve Number method (SCS-CN), CROPWAT model version 8 and Hazen model with an average daily rainfall data recorded from 1971 to 2016 were applied to estimate the runoff and water requirements in the study area. Findings of the study revealed that more than half rainfall water received in the catchment was lost through runoff (229.8 mm) and effective rainfall was lower (246.9 mm) than the actual crop water requirement for maize (330 mm). The expected seasonal surface runoff volume to be harvested by the farmers was 3008 m3 ha−1 per season and 1.29 × 106 m3 per season for the entire whole sub-catchment (430 ha). Based on Hazen model, the return period of low rainfall (dry spell) event would be expected every 2 years with a 98% probability of occurrence. Cyili sub-catchment has higher potential runoff volume to stabilize the deficit of water demand in the period of short rainy season. This suggests that rainwater harvesting through supplementary irrigation is an option to improve the crop yield in the dry period as well as in the annual dry season. Keywords: Available rainwater, Cyili sub-Catchment, Curve number, Runoff, Rwand

PROPIEDADES HIDRAULICASL DEL UN NITISOL EN KABETE, KENYA

Water relations are among the most important physical phenomena that affect the use of soils for agricultural, ecological, environmental, and engineering purposes. To formulate soil-water relationships, soil hydraulic properties are required as essential inputs. The most important hydraulic properties are the soil-water retention curve and the hydraulic conductivity. The objective of this study was to determine the soil hydraulic properties of a Nitisol, at Kabete Campus Field Station. Use of an internal drainage procedure to characterize the hydraulic properties and soil and water retention curves allowed for the establishment of the moisture and matric potential at field capacity and permanent wilting point. The Bt2 (84 -115) and Bt3 (115 - 143 cm) had the highest clay contents of 619 compared to Ap, AB and Bt1 horizons. The PWP was attained at soil moisture contents of 0.223, 0.284, 0277, 0.307 and 0.314 m3m-3 in the Ap, AB, Bt1, Bt2, and Bt3 horizons, respectively. Horizontal saturated hydraulic conductivity (Ksat) was high at 6.0 cm hr-1 in Ap horizon and decreased to 0.4 cm hr-1 in the subsurface horizon (Bt3). Ksat in the vertical direction was higher than horizontal and ranged from 8.3 cm hr-1 in surface layer to 0.6 cm hr-1 in Bt3 horizon, with exception of Bt1 and Bt2 where horizontal Ksat was greater than vertical. The Ap horizon also had the highest crop extractable water. Though the AB and Bt1 had the same water content at low matric suction, the variation was very wide as the SWRC approached saturation point. Bt1 and Bt2 also had similar water contents at suction range of – 7kPa after which Bt1, tended towards Bt3. Bt3 had the narrowest range of crop extractable water and thus was attributed to texture. The Bt3 retained the most amount of water at 0.314 m3m-3concluding that θPWP increased with depth. The total available water capacity between FC and PWP in the profile was 79.2 mm m-1. The study observed that the field capacity, crop available water contents and hydraulic conductivities were influenced positively by soil organic matter. The Van Genuchten parameters of air entry value (α) and pore size distribution (n) indicated that pore size distribution was not even in the AP and AB horizons. The field capacity was attained at higher matric potential at -5kPa for Bt1 while Bt2 and AP, AB, Bt2 and Bt3 was at -10kPa.The functional relationship, K(θ) = aθb that deals with water redistribution as a result of soil hydraulic properties and evaporative demand of the atmosphere was highly correlated to soil moisture content and texture with R2 values > 0.85