RP-Department of Environmental Science

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Adoption potential of selected organic resources for improving soil fertility in the central highlands of Kenya
(Springer Science+Business Media B.V., 2009) Mugwe, J.; Mucheru-Muna, M.; Mugendi, D.; Kung’u, J.B.; Bationo, A.; Mairura, F.
Soil fertility decline is the major cause of declining crop yields in the central highlands of Kenya and elsewhere within the African continent. This paper reports a study conducted to assess adoption potential of two leguminous trees, two herbaceous legumes, cattle manure, and Tithonia diversifolia either solely applied or combined with inorganic fertilizer, for replenishing soil fertility in the central highlands of Kenya. The study examined biophysical performance, profitability, feasibility and acceptability, and farmers experiences in managing and testing the inputs. The study was based on a series of studies incorporating both sociological and experimental approaches for two and a half years.Results of on farm trials showed that manure ? fertilizer and tithonia ? fertilizer treatments increased yields by more than 100% above the control. These treatments were the most profitable having highest net benefits and benefit cost ratios. They were also the most commonly preferred by farmers who used them on larger plots compared to the other inputs. In conclusion, cattle manure and tithonia were found to be the organic materials with the highest adoption potential for soil fertility improvement in this area. Calliandra calothyrsus and Leucaena trichandra, on the other hand, have potential for use as animal fodder. The herbaceous legumes had the least adoption potential due to poor performance recorded onthe farms that possibly led to low preference by the farmers. However, issues of sustainable seed production could have played a role. This study recommends some policy issues for enhancing adoption and research issues focusing on exploring strategies for increasing biomass production and use efficiency on farms.
Conservation tillage, local organic resources and nitrogen fertilizer combinations affect maize productivity, soil structure and nutrient balances in semi-arid Kenya
(Springer Netherlands, 2011-06) Mugendi, D.N.; Kihara, J.; Bationo, A.; Martius, C.; Vlek, P. L. G.
Smallholder land productivity in drylands can be increased by optimizing locally available resources, through nutrient enhancement and water conservation. In this study, we investigated the effect of tillage system, organic resource and chemical nitrogen fertilizer application on maize productivity in a sandy soil in eastern Kenya over four seasons. The objectives were to (1) determine effects of different tillage-organic resource combinations on soil structure and crop yield, (2) determine optimum organic–inorganic nutrient combinations for arid and semi-arid environments in Kenya and, (3) assess partial nutrient budgets of different soil, water and nutrient management practices using nutrient inflows and outflows. This experiment, initiated in the short rainy season of 2005, was a split plot design with 7 treatments involving combinations of tillage (tied-ridges, conventional tillage and no-till) and organic resource (1 t ha−1 manure + 1 t ha−1 crop residue and; 2 t ha−1 of manure (no crop residue) in the main plots. Chemical nitrogen fertilizer at 0 and 60 kg N ha−1 was used in sub-plots. Although average yield in no-till was by 30–65% lower than in conventional and tied-ridges during the initial two seasons, it achieved 7–40% higher yields than these tillage systems by season four. Combined application of 1 t ha−1 of crop residue and 1 t ha−1 of manure increased maize yield over sole application of manure at 2 t ha−1 by between 17 and 51% depending on the tillage system, for treatments without inorganic N fertilizer. Cumulative nutrients in harvested maize in the four seasons ranged from 77 to 196 kg N ha−1, 12 to 27 kg P ha−1 and 102 to 191 kg K ha−1, representing 23 and 62% of applied N in treatments with and without mineral fertilizer N respectively, 10% of applied P and 35% of applied K. Chemical nitrogen fertilizer application increased maize yields by 17–94%; the increases were significant in the first 3 seasons (P < 0.05). Tillage had significant effect on soil macro- (>2 mm) and micro-aggregates fractions (<250 μm >53 μm: P < 0.05), with aggregation indices following the order no-till > tied-ridges > conventional tillage. Also, combining crop residue and manure increased large macro-aggregates by 1.4–4.0 g 100 g−1 soil above manure only treatments. We conclude that even with modest organic resource application, and depending on the number of seasons of use, conservation tillage systems such as tied-ridges and no-till can be effective in improving crop yield, nutrient uptake and soil structure and that farmers are better off applying 1 t ha−1 each of crop residue and manure rather than sole manure.
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.
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.
Partial balance of nitrogen in a maize cropping system in humic nitisol of Central Kenya
(Kluwer Academic Publishers, 2006-11) Kimetu, J. M.; Mugendi, D.N.; Bationo, A.; Palm, C. A.; Mutuo, P. K.; Kihara, J.; Nandwa, S.; Giller, K.
The application of nitrogen in a soil under agricultural production is subject to several pathways including de-nitrification, leaching and recovery by an annual crop. This is as well greatly influenced by the management practices, nitrogen source and soil conditions. The main objective of this study was to investigate the loss of nitrogen (N) through nitrous oxide (N2O) emissions and mineral N leaching and uptake by annual crop as influenced by the N source. The study was carried out at Kabete in Central Kenya. Measurements were taken during the second season after two seasons of repeated application of N as urea and Tithonia diversifolia (tithonia) leaves. Results obtained indicated that nitrous oxide (N2O) emissions at 4 weeks after planting were as high as 12.3 μg N m −2 h−1 for tithonia treatment and 2.9 μg N m−2 h−1 for urea treatment. Tithonia green biomass treatment was found to emit N2O at relatively higher rate compared to urea treatment. This was only evident during the fourth week after treatment application.Soil mineral N content at the end of the season increased down the profile. This was evident in the three treatments (urea, tithonia and control) investigated in the study. Urea treatment exhibited significantly higher mineral N content down the soil profile (9% of the applied N) compared to tithonia (0.6% of the applied N). This was attributed to the washing down of the nitrate-N from the topsoil accumulating in the lower layers of the soil profile. However, there was no significant difference in N content down the soil profile between tithonia treatment and the control. It could be concluded that there was no nitrate leaching in the tithonia treatment. Nitrogen recovery by the maize crop was higher in the urea treatment (76% of the applied N) as compared to tithonia treatment (55.5% of the applied N). This was also true for the residual mineral N in the soil at the end of the season which was about 7.8% of the applied N in the urea treatment and 5.2% in the tithonia treatment.From this study, it was therefore evident that although there is relatively lower N recovery by maize supplied with tithonia green biomass compared to maize supplied with urea, more nitrogen is being lost (through leaching) from the soil–plant system in the urea applied plots than in tithonia applied plots. However, a greater percentage (37.8%) of the tithonia-applied N could not be accounted for and might have been entrapped in the soil organic matter unlike urea-applied N whose greater percentage (92%) could be accounted for.
Soil organic carbon dynamics, functions and management in West African agro-ecosystems
(2007-04) Vanlauwe, B.; Waswa, B.; Kimetu, J.; Kihara, J.; Bationo, A.
Soil fertility depletion has been described as the single most important constraint to food security in West Africa. Over half of the African population is rural and directly dependent on locally grown crops. Further, 28% of the population is chronically hungry and over half of people are living on less than US$ 1 per day as a result of soil fertility depletion. Soil organic carbon (SOC) is simultaneously a source and sink for nutrients and plays a vital role in soil fertility maintenance. In most parts of West Africa agro-ecosystems (except the forest zone), the soils are inherently low in SOC. The low SOC content is due to the low shoot and root growth of crops and natural vegetation, the rapid turnover rates of organic material as a result of high soil temperatures and fauna activity particularly termites and the low soil clay content. With kaolinite as the main clay type, the cation exchange capacity of the soils in this region, often less that 1 cmol kg−1, depends heavily on the SOC. There is a rapid decline of SOC levels with continuous cultivation. For the sandy soils, average annual losses may be as high as 4.7% whereas with sandy loam soils, losses are lower, with an average of 2%. To maintain food production for a rapidly growing population, application of mineral fertilizers and the effective recycling of organic amendments such as crop residues and manures are essential especially in the smallholder farming systems that rely predominantly on organic residues to maintain soil fertility. There is need to increase crop biomass at farm level and future research should focus on improvement of nutrient use efficiency in order to increase crop biomass. Research should also focus on ways of alleviating socio-economic constraints in order to increase the legume component in the cropping systems. This will produce higher quality fodder for the livestock and also increase biomass at farm-level. This paper reviews various strategies and lessons learnt in improving soil organic carbon status in West Africa soils.
Technologies for sustainable management of sandy Sahelian soils
(2014-07-15) Vanlauwe, B.; Kihara, J.; Waswa, B.; Bationo, A.; Ouattara, B.
Soil fertility is the most limiting factor for crop production in the Sahelian zone of West Africa. Over 95% of soils in this region are sandy and pose a great challenge to sustainable management. The poor structure and coarse texture of sandy soils results in low water holding capacity. Nutrient contents and nutrient retention are low, thus causing a low inherent fertility status for agricultural production. In the recent past, scientists have evaluated the potential of different technologies in addressing the soil fertility problems in the sandy Sahelian soils with the aim of increasing food production. Research results have shown that yields can be increased three to five times with the improvement of soil fertility using organic and inorganic fertilizers. Combinations of these materials also improve an array of other soil properties such as organic carbon content, cation exchange capacity (CEC) and pH. The main constraint to combining inorganic-organic materials is the high costs of inorganic fertilizers and the low availability of organic fertilizers at the farm level. Crop rotation and intercropping systems have also shown potential in increasing food production and improving soil fertility. Rotation systems increase biological nitrogen fixation and improve fertilizer use efficiency. The use of locally available phosphate rock, which could be an alternative to the use of high cost imported P fertilizers, has also shown potential for alleviating soil P limitations in these sandy soils, improving yields and the efficiency of N and water use. Hill placement of inorganic fertilizers and manure is superior to broadcasting. Fertilizer applied to crops in “micro-doses” and hill placed, combined with the use of crop residues and/or manure offers profitable natural resource management technologies to farmers. Successful experience from Niger has shown that adoption of microdose technology can increase production by more than 100% and farm incomes by 50% but requires supportive and complementary institutional innovation and market linkage. Combined water harvesting techniques and integrated nutrient management (INM) in the drier areas of the West African region clearly shows that higher yields can be achieved. In the Central Plateau of Burkina Faso, stone bunds alone doubled sorghum yield compared to the control and could reduce risks of crop failure in erratic rainfall years. A bottleneck to the use of these profitable soil fertility-enhancing technologies is the low capacity of farmers to invest in these technologies. In order to have these technologies to reach millions of farmers, a new integrated soil fertility management (ISFM) paradigm has been adopted which integrates biological, physical, chemical, social, economic and political factors. Future research challenges include strategies to increase the legume component for a better integration of crop-livestock production systems, exploiting genetic variation for nutrient use efficiency and integration of socio-economic and policy research with the technical solutions. Another very important issue for research is how to increase crop biomass availability at farm level to alleviate the constraint of non-availability of organic amendments. Use of decision support systems, modeling, and GIS are important in order to extrapolate research findings to other areas in which successful technologies can be expanded/scaled out to reach more farmers.

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