RP-Department of Environmental Science

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Potential role of cereal-legume intercropping systems in integrated soil fertility management in smallholder farming systems of sub-Saharan Africa
(Third RUFORUM Biennial Meeting, 201-09) Mucheru-Muna, M.; Matusso, J. M. M.; Mugwe, J. N.
The sub-Saharan Africa’s population is growing exponentially and it has to fulfill its food and nutrition requirement. An attractive strategy for increasing productivity and labour utilization per unit area of available land is to intensify land use. Intercropping is advanced as one of the integrated soil fertility management practices consisting of cultivating two or more crops in the same space at the same time, which have been practiced in past decades and achieved the goals of agriculture. Also, intercropping systems are beneficial to the smallholder farmers in the low-input and/or high-risk environment of the tropics, where intercropping of cereals and legumes is widespread among smallholder farmers due to the ability of the legume to contribute to addressing the problem of declining levels of soil fertility. The principal reasons for smallholder farmers to intercrop are flexibility, profit maximization, risk minimization, soil conservation and improvement of soil fertility, weed, pests and diseases control and balanced nutrition. This is a review paper that explores the role of cereal legume intercropping systems in integrated soil fertility management in smallholder farms of Sub-Saharan Africa. The intercropping systems are useful in terms of increasing productivity and profitability, water and radiation use efficiency, control of weeds, pests and diseases. The critical role of biological nitrogen fixation and the amounts of N transferred to associated non-leguminous crops determines the extent of benefits. In intercropping, land equivalent ratio (LER), benefit cost ratio (BCR) and monetary advantage index (MAI) are used to assess the productivity and its economic benefits. In this study, the work carried out by various researchers about different intercropping system is discussed, and it would be beneficial to the researchers who are involved in this field.
Intracavity pulse compression with glass: a new method of generating pulses shorter than 60 fsec
(Optical Society of America, 1983) Diels, J.C.; Fontaine, J. J.; Dietel, W.
The introduction of a glass prism in a ring dye laser is shown to provide simultaneous wavelength selection and pulse compression.
Functional Evaluation of Pedotransfer Functions for the Estimation of Soil Hydraulic Properties
(Elsevier, 1992-09) Diels, J.; Vereecken, H.; VOrshoven, J. V.; Feyen, J.; Bouma, J.
Pedotransfer functions (PTFs) are often used for estimating hydraulic properties such as the moisture retention characteristic and the pressure head-hydraulic conductivity relationship. Both properties are essential for the description of water and solute movement in unsaturated soils. Frequently, PTFs are not evaluated with respect to specific applications. The criteria, presently used to evaluate the goodness of fit for a PTF do not provide information about the performance of these functions for applications such as the prediction of the downward water flux below the soil root zone or of the soil moisture deficit during the growing season. We performed functional evaluations of PTFs. In a first sample problem, the influence of uncertainty in the PTF was examined on the basis of two functional criteria: the moisture supply capacity (MSC) and the downward flux below the root zone (DFR). In a second sample problem the effect of the uncertainty in the PTFs and the variability in soil properties within a map unit on the simulated MSC distributions were analyzed. The MSC distributions were calculated and compared for two map units known by soil surveyors to differ considerably during a dry year. It was found that an improved estimate of the hydraulic properties, obtained by calibrating PTFs using detailed textural information, did not substantially reduce the dispersion of the MSC and DFR distributions. Results from the second sample problem indicated that >90% of the variation in the simulated MSC was caused by estimation errors in the hydraulic properties, overwhelming the map unit variability.
A deterministic evaluation analysis applied to an integrated soil-crop model
(Elsevier, 1995-08) Diels, J.; Feyen, J.; Viaene, P.; Vanclooster, M.
The WAVE-model (Water and Agrochemicals in the soil and Vadose Environment), simulating one-dimensional transport of water, solute and heat in the unsaturated zone, was used to simulate the behaviour of water and nitrogen in soils cropped with winter wheat and sugar beet. Soil water transport was modelled using the Richards equation, while solute transport was described with a convection equation. Soil mineral nitrogen transformations were simulated using first-order kinetics, while for the organic matter turnover three organic matter pools were considered. A summary model was used to simulate crop growth. The performance of the integrated model was evaluated in a deterministic way using field data for a three-year period. The data of the first year were used for the model calibration. The remaining set of data was used to evaluate the capacity of the model to predict soil water content, the soil nitrate-N content, the soil ammonia-N content, the soil temperature, the soil water pressure head, the leaf area development and the dry matter accumulation in different plant organs. A screening sensitivity analysis indicated that the calculated nitrogen balance was sensitive to the soil hydraulic properties and the crop Kc-factors for the given scenario. The effect of uncertainty of the sensitive hydraulic properties on the calculated nitrogen balance was investigated using Monte Carlo simulation. Taken into consideration the variability on the soil hydraulic parameters, predicted nitrate-N flux out of the soil profile at a depth of one meter ranged for the simulated period (three years) between −10 and +10 kg ha−1.
Impact of residue quality on the C and N mineralization of leaf and root residues of three agroforestry species
(Springer Verlag, 1996) Vanlauwe, B.; Nwoke, O. C.; Sanginga, N.; Merckx, R.
A laboratory incubation experiment with 15N labeled root and leaf residues of 3 agroforestry species (Leucaena leucocephala, Dactyladenia barteri and Flemingia macrophylla) was conducted under controlled conditions (25 C) for 56 days to quantify residue C and N mineralization and its relationship with residue quality. No uniform relation was found between the chemical composition of the above and below residues. The leucaena and dactyladenia roots contained more lignin (8 and 26% respectively) and less N (2.0 and 1.0% respectively) than the respective leaves (2 and 13% lignin and 2.9 and 1.4% N, respectively), whereas the differences between the lignin and N contents of the flemingia leaves and roots were not significant (4.6 and 3.0% lignin and 2.63 and 2.68% N, respectively). The leucaena leaves contained more polyphenols than the roots (6.4 and 3.6%), while the polyphenol content of the leaves and roots of the other residues was similar (5.0 and 5.1% for dactyladenia and 4.0 and 3.5% for flemingia). Three patterns of N mineralization could be distinguished. A first pattern, followed by residues producing the highest amounts of CO2, showed an initial immobilization of soil derived N, followed by a net release of both soil and residue derived N after 7 days of incubation. A second pattern, followed by the flemingia leaf residues which produced intermediate amounts of CO2 and had an intermediate quality, showed no significant immobilization of soil derived N, and significant mineralization of residue N. A third pattern, followed by both low quality dactyladenia residues, showed a low release of residue derived N and a continued inmobilization of soil derived N. Residue C mineralization was significantly (p<0.05) correlated with the residue lignin content, C-to-N ratio, and polyphenol-to-N ratio. The proportion of residue N mineralized (immobilized) after 56 days of incubation was significantly correlated with the residue N content (p<0.01) and the C-to-N ratio (p<0.05). The relations were quadratic, rather than linear. The ratio of the proportion of residue N mineralized (immobilized) over the proportion of residue C mineralized after 56 days was highly significantly correlated with the lignin content (p<0.01) and C-to-N (p<0.001), lignin-to-N (p<0.01), polyphenol-to-N (p<0.01) and (lignin+polyphenol)-to-N ratios (p<0.01) in a linear way. This indicates that due to the low availability of the residue C, relatively less N is immobilized for the very low quality residues ((lignin+polyphenol)-to-N ratio: 29.7) than for the residues with a relatively higher quality ((lignin+polyphenol)-to-N ratios between 3.3 and 12.5).
Dispersion measurements with white-light interferometry
(1996) Diels, J.C.; Diddams, S.
White-light interferograms provide a simple, accurate, and physically intuitive picture of what happens to broadband optical pulses on transmission through, or reflection from, common optical materials. Quantitative measurement of group delay are made with an accuracy of ±0.1 fs and with high spectral resolution. This measurement accuracy is applied to the determination of d2n/dλ2 and d3n/dλ3 of fused silica with an accuracy of ±5 × 10−5 µm−2 and ±1 × 10−3 µm−3, respectively. Further applications are found in the measurement of the dispersion of broadband mirrors and a multiple-quantum-well structure.
Predicting the Decomposition Patterns of Tree Biomass in Tropical Highland Microregions of Kenya
(Kluwer Academic Publishers, 1996) Mugendi, D.N.; Nair, P. K. R.
Decomposition- and nitrogen-release patterns of biomass from three agroforestry multipurpose trees (Calliandra calothyrsus, Cordia africana and Grevillea robusta) were investigated in four contrasting environments (microregions) in the Kenyan tropical highlands during two cropping seasons. Dried leafy biomass was placed in 2-mm litter bags, buried at 15-cm depth and recovered after 2, 4, 7, 10, 15 and 20 weeks. Decomposition patterns were best described by first-order exponential decline curves. The decomposition rate constants ranged from 2.1 to 8.2 yr−1, and the rates of decomposition among the species were in the order: calliandra ≥ cordia > grevillea. There was a species-by-environment interaction during both seasons, but the nitrogen released did not follow such a pattern. Among the three tree species, calliandra released the highest amount of cumulative N, followed by cordia and grevillea. Using multiple regression techniques, decomposition pattern was described as a function of three groups of factors: biomass quality (N, C, lignin and polyphenol), climate (soil temperature and rainfall), and soil conditions (pH, soil organic C, total N and P). For all the species and factors combined, the adjusted R 2 values were 0.88 and 0.91 for seasons 1 and 2, respectively. Among the three groups of factors, climate and biomass quality had the most influence on decomposition rates. Climatic factors accounted for 75% of the total rate of decomposition in season 1 (‘irregular’ season with less rainfall and more soil temperature fluctuations), whereas biomass quality factors were more influential in season 2 (‘regular’ season), accounting for 65% of the total variability.
Alley cropping of maize with calliandra and leucaena in the subhumid highlands of Kenya: Part 2. Biomass decomposition, N mineralization, and N uptake by maize
(Kluwer Academic Publishers, 1999) Mugendi, D.N.; Nair, P. K. R.; Mugwe, J. N.; O'Neill, M. K.; Swift, M. J.; Woomer, P.
A major challenge in developing agroforestry approaches that utilize tree-leaf biomass for provision of N to crops is to ensure synchrony between the N released from decomposing prunings and N demand by crops. A study was conducted in the subhumid highlands of Kenya to assess the rate of decomposition and mineralization of soil-incorporated Calliandra calothyrsus Meissner (calliandra) and Leucaena leucocephala (Lam.) de Wit (leucaena) tree biomass and maize roots (Zea mays L.) both in an alley cropping and a sole cropping system. The amount of mineralized N peaked four weeks after planting (WAP) maize in all the treatments during both seasons of 1995. Cumulative mineralized N at week 20 ranged from 114 to 364 kg N ha−1 season−1, the absolute control treatment giving the lowest and the prunings-incorporated treatments giving the highest amounts in the two seasons. Total N uptake by maize, ranging from 42 to 157 kg ha−1 season−1, was lowest in the 'alley-cropped, prunings-removed' treatments, and highest in the 'non alley-cropped-prunings-incorporated' treatments. The apparent N recovery rate by maize was highest in the fertilizer applied treatments in the two seasons. Decomposition rate constants (kD) ranged from 0.07 to 0.21 week−1, and the rates among the different plant residues were as follows: leucaena < calliandra < maize roots. Nitrogen release rate constants (kN), ranging from 0.04 to 0.25 week−1, followed a similar pattern as the rate of decomposition with leucaena releasing the highest amount of N followed by calliandra and lastly by maize roots.
Adolescent transition to coitus and premarital childbearing in sudan: a biosocial context
(Cambridge University Press, 1999) Otor, S.C.J.; Pandey, Arvind
The effects of woodfuel consumption in the ASAL areas of kenya: the case of marsabit forest
(Wiley, 2000-03) Kirubi, C.; Wamicha, W. N.; Laichena, Justus K.
In the arid and semiarid lands (ASAL) of Kenya, fuelwood and charcoal constitute 95–98% of the total energy demand for cooking, heating and lighting. The resultant deleterious ecological effects are severe and need urgent remedial interventions. A study was carried out in Marsabit District, which is a vast ASAL region, to examine the effects of woodfuel consumption on Marsabit Forest and the surrounding areas. It was found that wood for fuel harvested from Marsabit Forest was approximately 56,000 tons y−1. The rate of deforestation was estimated at 1.6 ha y−1. This resulted in great loss of indigenous biodiversity, destruction of vital ecosystems and habitats. To control further degradation of the forest, it is recommended that an immediate ban be imposed to stop harvesting of the indigenous species such as Olea spp. and Teclea spp., which are seriously endangered. Also, woodfuel conservation through wider and more efficient use of the improved energy-saving technologies should be enhanced.
Nitrogen recovery by alley-cropped maize and trees from 15N-labeled tree biomass in the subhumid highlands of Kenya
(Springer-Verlag, 2000-05) Mugendi, D.N.; Nair, P. K. R.; Graetz, D. A.; Mugwe, J. N.; O'Neill, M. K.
The effectiveness of tree-leaf biomass as a source of N to crops in agroforestry systems depends on the rate at which crops can obtain N from the biomass. A study was conducted to determine the fate of 15N labeled, soil-applied biomass of two hedgerow species, Calliandra calothyrsus Meissner (calliandra) and Leucaena leucocephala (Lam.) de Wit (leucaena), in the subhumid highlands of Kenya. Labeled biomass obtained from 15N fertilized trees was applied to microplots in an alley cropping field and maize planted. N uptake and recovery by maize and hedgerow trees was periodically determined over a 20-week period during the short rain (1995) and the long rain (1996) growing seasons. In maize crop from treatments that received leucaena biomass, higher N uptake and recovery were recorded than in maize from the plots that received calliandra biomass. However, N uptake and recovery were higher in calliandra tree hedges than in leucaena hedges, indicating differences in N uptake by the two tree species. The largest fraction (55–69%) of N in the applied tree biomass was left in the soil N pool, 8–13% recovered by maize, 2–3% by tree hedges, and 20–30% could not be accounted for. Some of the unaccounted for N may have been left in the wood and root portions of the tree hedges and in the bulk soil below the 20-cm depth. The study shows that only a small fraction of the N contained in the N-rich biomass that is applied to the soil is taken up by the current season's crop, suggesting that a major benefit may be in the build-up of the soil N store.
Phenotypic nutrient up-take differences in an alley cropping system in semi-arid Machakos, Kenya
(IOS Press, 2001-01-01) Mugendi, D.N.
Alley cropping of Cassia siamea and maize was studied in semi-arid Kenya for soil fertility improvement. Katumani composite maize was planted except in the short rains of 1988 (SR88) when a hybrid variety was sown. Therefore the grain yield per row increased differently in the alley cropped maize (CM). Sole maize (SM) and CM yields were higher in SR88 than in the long rains of 1988 (LR88) by 62% and 38%, while yields from the same treatments in LR89 were only 21% and 45% of those in SR88. These differences in relative maize yields are attributed to differences between the two maize varieties in competition under nutrient stress conditions.
Suppression of Root-knot Nematode by Mycosymbionts on Pyrethrum (Chrysanthemum cinerariefolium Vis.)
(AJOL, 2002) Waceke, W.; Waudo, S. W.; Sikora, R.
Five arbuscular mycorrhiza fungi (AMF) obtained from pyrethrum fields were screened for efficacy in improving pyrethrum (Chrysanthemum cinerariefolium Vis.) growth and in suppressing a root-knot nematode, Meloidogyne hapla Chitwood in the greenhouse. The fungi screened were Glomus macrocarpum Tul and Tul, G. constrictumTrappe, G. monosporum Gerd. & Trappe, Scutellospora calospora (Nicol. Gerd.) Walker & Sanders and Gigaspora gigantea (Nicol. Gerd.) Gerd. & Trappe. A mixed fungal inoculum was incorporated into sterilized sand-soil mixture before transplanting 6-week-old pyrethrum seedlings. The inoculum consisted of the growth medium, spores, external mycelia and infected root segments. The plants were inoculated with 6000 M. hapla second stage juvenile (J-2) 3 months after fungal inoculation. Dry shoot weights, fresh root weights, percent root colonization by the fungi, nematode gall indices, number of eggs and females in the root system and number of J-2 in the soil were determined at the end of the experiment, 2 months after nematode inoculation. Glomus macrocarpum and S. calospora significantly improved top biomasses of fungus-treated and fungusnematode- treated plants. Glomus macrocarpum was the most effective, causing a 35% top biomass increase. Glomus constrictum, G. monosporum and G. gigantea improved top biomasses of fungusnematode- treated plants. Scutellospora calospora and G. constrictum significantly increased fresh root weights of pyrethrum by 46% and 53%, respectively. Except G. constrictum and G. monosporum, all the other fungi suppressed M. hapla disease severity and egg production. Glomus macrocarpum was the most effective, causing 87% nematode suppression. Scutellospora calospora and Gigaspora gigantea suppressed disease severity and egg production by up to 33% and 37%, respectively. All the fungi significantly reduced the number of females and J-2 in pyrethrum roots. Nematodes did not affect root colonization by the fungi except in G. constrictum and G. monosporum-colonized plants.
Enhancement of food productivity using leguminous shrubs in the Eastern highlands of Kenya
(Elsevier, 2003) Mugendi, D.N.; Mucheru-Muna, M.; Mugwe, J. N.; Bationo, A.
Declining soil productivity is a major challenge facing smallholder farmers in eastern highlands of Kenya. This decline is caused by continuous cultivation of soils without adequate addition of external inputs in form of manures and fertilizers. A study was initiated in 1992 to evaluate the feasibility of using two leguminous shrubs Calliandria (Calliandra calothyrsus ) and Leucaenia ( Leucaena leucocephala ) for improving soil productivity. The shrubs were evaluated in alley cropping and biomass transfer systems. Over the 11 years of study, calliandra and leucaena biomass transfer with half recommended rate of inorganic fertiliser treatments gave the best average maize yields of 3.2 t ha -1 . On the other hand calliandra alley cropped with prunings removed treatment recorded the lowest maize yield of 1.2 t ha -1 . Though treatments with calliandra biomass transfer had similar yields compared to those of leucaena biomass transfer, all the treatments that were leucaena alley cropped did better than calliandra alley cropped treatments both with prunings incorporated and prunings removed. These long-term results indicate that biomass transfer system of these leguminous shrubs is a more feasible option as opposed to alley cropping in the region.
Soil Invertebrate Macrofauna Composition within Agroforestry and Forested Ecosystems and their Role in Litter Decomposition in Embu, Kenya
(CIAT, 2004) Mugendi, D.N.; Mwangi, M.; Kung'u, J.B.; Swift, M. J.; Albrecht, A.
Adequate food to meet the needs of an ever-increasing population is a major challenge for most developing countries, especially in the tropics. Despite this, few new technical packages capable of increasing net returns without deteriorating the environment have been developed. Crop yields in Embu, Kenya are poor due to declining soil fertility prompted by continuous cropping and application of fertilizers in non-sufficient quantities by farmers. Studies have shown that soil biota provides the means and regulates the transformation of organically bound nutrients into plantavailable forms through mineralization. An experiment was conducted to investigate soil macrofauna composition within agroforestry and forested ecosystems and their role in litter decomposition. This was anticipated to address poor crop yields in the study region. The study was conducted during the long and the short rains of the year 2000 on-station at Embu in an ongoing hedgerow intercropping experiment. Two types of Standard PVC litterbags with mesh size 7 mm and 1mm, were used. The 7 mm mesh size allowed macrofauna to enter while the 1 mm excluded the macrofauna. Two types of litter: Calliandra calothyrsus (low quality) and Leucaena leucocephala (high quality), were placed in the litterbags in duplicate in selected treatments of the Embu trials and were sampled at 1, 2, 4, 8, and 16 weeks. Decomposition rate constants (k) were estimated using a non-linear module in the EXCEL spreadsheet upon fitting first order exponential equations. Results from the study depicted that different management practice and/or land use affect soil macrofauna in varied manner. Soil invertebrate macrofauna enhanced the rate of decomposition of C. calothyrsus and L. leucocephala litter.
Nitrogen fertilizer equivalencies of organics of differing quality and optimum combination with inorganic nitrogen source in Central Kenya
(Kluwer Academic Publishers, 2004-02) Mugendi, D.N.; Kimetu, J.M.; Palm, C.A.; Mutuo, P.K.; Gachengo, C.N.; Bationo, A.; Nandwa, S.; Kung'u, J.B.
Decline in crop yields is a major problem facing smallholder farmers in Kenya and the entire Sub-Saharan region. This is attributed mainly to the mining of major nutrients due to continuous cropping without addition of adequate external nutrients. In most cases inorganic fertilizers are expensive, hence unaffordable to most smallholder farmers. Although organic nutrient sources are available, information about their potential use is scanty. A field experiment was set up in the sub-humid highlands of Kenya to establish the chemical fertilizer equivalency values of different organic materials based on their quality. The experiment consisted of maize plots to which freshly collected leaves of Tithonia diversifolia (tithonia), Senna spectabilis (senna) and Calliandra calothyrsus (calliandra) (all with %N>3) obtained from hedgerows grown ex situ (biomass transfer) and urea (inorganic nitrogen source) were applied. Results obtained for the cumulative above ground biomass yield for three seasons indicated that a combination of both organic and inorganic nutrient source gave higher maize biomass yield than when each was applied separately. Above ground biomass yield production in maize (t ha−1) from organic and inorganic fertilization was in the order of senna+urea (31.2), tithonia+urea (29.4), calliandra+urea (29.3), tithonia (28.6), senna (27.9), urea (27.4), calliandra (25.9), and control (22.5) for three cumulative seasons. On average, the three organic materials (calliandra, senna and tithonia) gave fertilizer equivalency values for the nitrogen contained in them of 50, 87 and 118%, respectively. It is therefore recommended that tithonia biomass be used in place of mineral fertilizer as a source of nitrogen. The high equivalency values can be attributed to the synergetic effects of nutrient supply, and improved moisture and soil physical conditions of the mulch. However, for sustainable agricultural production, combination with mineral fertilizer would be the best option.
Impact of water quality on macroinvertebrate assemblages along a tropical stream in Kenya
(Wiley, 2004-09) Ndaruga, Ayub Macharia; Ndiritu, G. G.; Wamicha, W. N.; Gichuki, N. N.
Prudent management of lotic systems requires information on their ecological status that can be estimated by monitoring water quality and biodiversity attributes. To understand environmental conditions in Gatharaini drainage basin in Central Kenya, a study was carried out to establish the relationship between water quality and macroinvertebrate assemblages between the months of March and September 1996. Six sampling sites, each 25 m long were selected along a 24-km stretch of the stream, which drained land under agricultural, residential and industrial use. Water physico-chemical data was explored using multivariate analysis of Principal Component Analysis to detect environmental trends downstream. Both macroinvertebrates and water physico-chemical data of suggested trends were analysed for variations and correlations. Temperatures and invertebrate densities changed significantly between the dry and wet season (P < 0.01) but the fluctuations were not evident downstream. Water physico-chemical characteristics (total dissolved solids (TDS), pH, turbidity, dissolved oxygen) and biodiversity indices (species richness, diversity, dominance, evenness) changed markedly downstream (P < 0.01). Biodiversity indices correlated inversely with TDS, pH and turbidity but positively with dissolved O2. It was evident macroinvertebrate assemblages changed significantly downstream as opposed to functional feeding groups. Diptera was important in most sites whilst Oligochaeta dominance increased downstream corresponding to the deterioration in water quality. Collectors/browsers were the dominant functional feeding groups at most sites. This study showed that significant changes in aquatic macroinvertebrate assemblages were primarily due to water quality rather than prevailing climatic conditions.
Uses and conservation of some highland species of the genus Sansevieria Thunb in Kenya
(African Crop Science Society, 2005) Khalumba, Mercelyne Luxen; Mbugua, P.K.; Kung'u, J.B.
Approximately 75 species constitute Sansevieria Thunb, a tropical terrestrial genus of Asparagaceae Juss family. About 40 of these species are found in E.A, while 27 are endemic to Kenya. Information on ethnobotany and conservation of these species in Kenya is limited and in order to conserve wild plants they must carefully be documented. The selected species were: Sansevieria suffruticosa, Sansevieria parva, Sansevieria raffillii and Sansevieria ehrenbergii growing naturally in Nakuru and Maragua districts. Data was collected by means of a questionnaire and observation schedules. The results indicate that leaves of S. suffruticosa and S. ehrenbergii were valued for treatment of ear-ache (78%) and open fresh wounds (94%), while their rhizomes are used to treat snakebites (36%) and stomach ulcers (20%). The results indicate that Sansevieria fibres can be used for weaving (51%). Man is the main threat of Sansevieria species in the field destroying over (80%).
Water Resources Utilization, Conflicts and Interventions in the Tana Basin of Kenya
(FWU Water Resources Publications, 2005) Agwata, J. F.
Water is an essential resource necessary for social and economic development of any country. When it is available in sufficient quantities and acceptable quality, it is extensively used for domestic, agricultural and industrial purposes. Some of the uses include drinking; washing, watering of livestock, growing crops and the manufacture of finished goods in industry. In Kenya, adequate water is available only in 20% of the country’s landmass whilst in the rest and biggest portion of the country including the arid and semi-arid lands, it has to be mined from the ground or harvested in dams, and pans. Due to the scarcity of water in the arid and semi-arid regions of the country and its uneven and poor distribution in the high and medium potential areas, its utilization for various functions in any basin often leads to conflicts. These conflicts require appropriate interventions in the form of conservation, protection of water sources and apportionment to meet various water needs in an integrated and sustainable manner. In this paper, a brief overview of the water resources in Kenya is provided and the utilization of water in the Tana Basin and the associated conflicts and interventions examined. The main issues related to water in the basin should be addressed to ensure that the available water is managed in an integrated manner. Also, some of the necessary institutional frameworks for integrated and sustainable water resource management in the basin are proposed.
Exploring diversity in soil fertility management of smallholder farms in western Kenya: I. Heterogeneity at region and farm scale
(Elsevier Masson, 2005-11) Vanlauwe, B.; Tittonell, P.; Leffelaar, P.A.; Rowe, E.C.; Giller, K.E.
The processes of nutrient depletion and soil degradation that limit productivity of smallholder African farms are spatially heterogeneous. Causes of variability in soil fertility management at different scales of analysis are both biophysical and socio-economic. Such heterogeneity is categorised in this study, which quantifies its impact on nutrient flows and soil fertility status at region and farm scales, as a first step in identifying spatial and temporal niches for targeting of soil fertility management strategies and technologies. Transects for soil profile observation, participatory rural appraisal techniques and classical soil sampling and chemical analysis were sampled across 60 farms in three sub-locations (Emuhaia, Shinyalu, Aludeka), which together represent much of the variability found in the highlands of western Kenya. Five representative farm types were identified using socio-economic information and considering production activities, household objectives and the main constraints faced by farmers. Soil fertility management and nutrient resource flows were studied for each farm type and related to differences in soil fertility status at farm scale. Farm types 1 and 2 were the wealthiest; the former relied on off-farm income and farmed small pieces of land (0.6–1.1 ha) while the latter farmed relatively large land areas (1.6–3.8 ha) mainly with cash crops. The poorest farm type 5 also farmed small pieces of land (0.4–1.0 ha) but relied on low wages derived from working for wealthier farmers. Both farm types 1 and 5 relied on off-farm earnings and sold the least amounts of farm produce to the market, though the magnitude of their cash, labour and nutrient flows was contrasting. Farms of types 3 and 4 were intermediate in size and wealth, and represented different crop production strategies for self-consumption and the market. Average grain yields fluctuated around 1 t ha−1 year−1 for all farm types and sub-locations. Grain production by farms of types 4 and 5 was much below annual family requirements, estimated at 170 kg person−1 year−1. Household wealth and production orientation affected the pattern of resource flow at farm scale. In the land-constrained farms of type 1, mineral fertilisers were often used more intensively (ca. 50 kg ha−1), though with varying application rates (14–92 kg ha−1). The use of animal manure in such small farms (e.g. 2.2 t year−1) represented intensities of use of up to 8 t ha−1, and a net accumulation of C and macronutrients brought into the farm by livestock. In farms of type 5, intensities of use of mineral and organic fertilisers ranged between 0–12 kg ha−1 and 0–0.5 t ha−1, respectively. A consistent trend of decreasing input use from farm types 1–5 was generally observed, but nutrient resources and land management practices (e.g. fallow) differed enormously between sub-locations. Inputs of nutrients were almost nil in Aludeka farms. Both inherent soil properties and management explained the variability found in soil fertility status. Texture explained the variation observed in soil C and related total N between sub-locations, whereas P availability varied mainly between farm types as affected by input use.

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