C. O. Othieno

Tithonia and senna green manures and inorganic fertilizers as phosphorus sources for maize in Western Kenya

Efforts to overcome declining soil fertility on small holder farms in western Kenya must be consistent with the reality of low utilization of inorganic fertilizers. Likewise organic inputs alone cannot supply adequate nutrients. The use of two organic resources, Tithonia diversifolia (tithonia) and Senna spectabilis (senna) leaves, and their combination with inorganic P for improving soil fertility and maize yields was investigated on a P limiting soil in Western Kenya. Treatments included: 1) control, no inputs; 2) 5 t ha−1 (dry matter) tithonia leaves; 3) 5 t ha−1 senna leaves; 4) 5 t ha−1 tithonia leaves + 25 kg P ha−1 as triple superphosphate (TSP); 5) 5 t ha−1 senna leaves + 25 kg P ha−1 (as TSP); and 6) 25 kg P ha−1 of TSP. Maize was used as a test crop. Decomposition and P and N release of tithonia and senna leaves were determined in a litterbag study. Tithonia + TSP applications tripled maize yields compared to the control, senna + TSP and tithonia sole application doubled yields, while senna sole applications did not increase yields substantially. A large residual yield was produced in the tithonia treatments in a subsequent crop. These yield results were consistent with the higher quality and faster release of N and P from the tithonia leaves compared to senna. The tithonia biomass transfer system can improve yields in the short term but has limitations because of the large amount of biomass and the associated labor requirements.

Effect of combining organic residues with Minjingu phosphate rock on sorption and availability of phosphorus and maize production in acid soils of western Kenya

Experiments were conducted in both the greenhouse and the field on highly weathered (Orthic Ferralsol) soils to evaluate the effect of combining on-farm organic residues (chicken manure, farmyard manure, sugar bagasse) with Minjingu phosphate rock (MPR) on soil pH, extractable (available) and sorbed phosphorus (P), and to assess the cost benefit for maize production. The greenhouse study results indicated that, in the first eight weeks of incubation, soil pH increased linearly with increase in MPR rates and decreased thereafter. The available P also increased linearly. Chicken manure and sugar bagasse were most and least effective respectively in reducing P sorption, while there was a significant negative relationship between P adsorption maxima and extractable P. The field experiment data showed that the available P values increased significantly above the control in all the treatments where MPR and organic materials were applied separately or combined. Treatment effects on Langmuir sorption maxima (S max ) in the field were variable. An increase in S max with an increase in MPR rates was noted. However, there was a positive relationship between S max and available P ( r = 0.52 to 0.69), suggesting the diversity of factors affecting the complex nature of P dynamics under field conditions. MPR applied alone in the first season gave a significant residual positive effect on maize grain yield for two additional seasons. The economic analysis revealed that a single application of chicken manure (2 t ha −1 ) combined with MPR at 60 kg P ha −1 gave the highest incremental net benefit equivalent to US

Efficacy of soil solarization, Trichoderma harzianum, and coffee pulp amendment against Armillaria sp

657 ha −1 during the three maize cropping seasons.

EFFECTS OF COMBINING ORGANIC MATERIALS WITH INORGANIC PHOSPHORUS SOURCES ON MAIZE YIELD AND FINANCIAL BENEFITS IN WESTERN KENYA

Soil solarization was evaluated singly or in combination with Trichoderma harzianum infestation or coffee pulp amendment for its effect on wood-borne inoculum of an Armillaria sp. pathogenic on tea. Solarization increased maximum soil temperatures at 10 cm depth by 9-12degreesC and reduced viability of Armillaria sp. up to 100%. Its efficacy was similar at 5, 10, and 15 cm soil depths. Trichoderma harzianum applied to the soil surrounding the blocks of inoculum also significantly reduced viability of the pathogen. Application of 20g of the wheat bran culture of the antagonist in every 1000cm(3) of soil surrounding the blocks of inoculum, following solarization for 5 week, caused total loss of Armillaria inoculum viability and was similar to 10 week of solarization without application of the antagonist. The coffee pulp amendment reduced inoculum viability slightly though this effect was apparent only in non-solarized soil

Comparison of effects of phosphorus sources on soil acidity, available phosphorus and maize yields at two sites in western Kenya

Due to escalating costs of imported fertilizers, there is renewed interest in the use of local nutrient resources in managing soil fertility in Kenya. We tested the effect of two organic materials, farmyard manure (FYM) and Tithonia diversifolia (tithonia), and an inorganic N fertilizer, urea, when applied alone or in combination with three inorganic P sources, triple superphosphate (TSP), Minjingu phosphate rock (MPR) and Busumbu phosphate rock (BPR), on maize yields and financial benefits. The study was conducted for three consecutive seasons, from March 2007 to August 2008 in western Kenya. FYM and tithonia were applied to supply 20 kg P ha −1 in treatments where they were used either alone or in combination with the inorganic P sources while 40 kg P ha −1 was from the inorganic P sources in the combination. Where urea was used, the inorganic P sources were applied at 60 kg P ha −1 . When applied in combination with urea, MPR was a better P source for maize than TSP or BPR. However, when applied in combination with FYM or tithonia, TSP was the best P source. Treatments including tithonia were more effective in increasing maize yields than those without it with a similar total P application rate. The agronomic effectiveness of tithonia did not, however, translate to economic attractiveness, mainly due to very high labour costs associated with its use. FYM when applied alone at 20 kg P ha −1 was the only treatment that exceeded a benefit:cost ratio of 2 and, therefore, the most likely, of the tested technologies to be adopted by farmers.

Occurrence and genetic diversity of phosphate-solubilizing bacteria in soils of differing chemical characteristics in Kenya

The effects of farmyard manure (FYM), Tithonia diversifolia (tithonia) and urea when applied alone or in combination with Minjingu phosphate rock (MPR), Busumbu phosphate rock (BPR) or triple superphosphate (TSP) on soil acidity, P availability, maize yields and financial benefits were evaluated at Bukura and Kakamega in western Kenya. A reduction in exchangeable acidity and Al was observed in most tithonia- and FYM-treated soils, but not with inorganic P sources when applied in combination with urea. The effectiveness in increasing available soil P followed the order; TSP > MPR > BPR among inorganic P sources, and FYM > tithonia among organic materials at both sites. At Bukura, a site higher in both available P and Al saturation compared with Kakamega, maize did not respond to inorganic P sources applied in combination with urea. Maize, however, responded when inorganic P sources were applied in combination with FYM or tithonia at this site. At Kakamega, maize responded to TSP but not to MPR or BPR when applied with urea. Application of TSP in combination with tithonia gave the highest maize yields at both sites. Of the tested technologies, only FYM when applied alone at Bukura was economically attractive.

Screening of sesbania for tolerance to aluminum toxicity and symbiotic effectiveness with acid tolerant rhizobia strains in acid soil in Western Kenya.

This study focused on the isolation, identification (sequencing of 16S rDNA gene) and determination of the phosphorus (P)-solubilizing efficiency of native populations of phosphate-solubilizing bacteria (PSB) in 13 Kenyan soils with differing chemical characteristics. Air-dried soil samples were serially diluted and plated on NBRIP media and enumerated. Their phosphate-solubilizing efficiency was assessed on Frioni’s agar. Pearson correlation coefficients were determined between PSB populations and soil properties. The PSB populations varied among the sites tested and had a positive and significant correlation (p ≤ 0.05) with organic carbon (r = 0.76), exchangeable calcium (r = 0.93) and exchangeable magnesium (r = 0.92). A total of 150 isolates were identified to the genus and species level. Among the isolates, Bacillus megaterium, Bacillus sp. and Arthrobacter sp. were the most abundant and well-distributed strains. However, only 5% of the total isolates were efficient in terms of phosphate-solubilizing efficiency. The results indicate that although there were many PSB strains in the soils tested, only a few (5%) were effective in terms of their phosphate-solubilizing ability. It is therefore unlikely that native PSB contribute significantly to solubilizing phosphate in the soils tested, which would ultimately benefit plant growth. Therefore, inoculation with effective strains with a high P solubilization potential is necessary.

The Potential of Increased Maize and Soybean Production in Uasin Gishu District, Kenya, Resulting from Soil Acidity Amendment Using Minjingu Phosphate Rock and Agricultural Lime

Nitrogen fixation by leguminous trees such as sesbania ( Sesbania sesban ) in acid soils is limited by aluminium (Al) toxicity and phosphorus (P) deficiency. We screened 214 East African sesbania accessions for Al toxicity tolerance, P use efficiency and sesbania–rhizobia symbiosis. Aluminium toxicity tolerance or sensitivity was measured by the relative root elongation index. Highly Al tolerant and sensitive accessions were screened for P use efficiency. Highly P use efficient and Al sensitive accessions were assessed for symbiotic effectiveness with acid tolerant rhizobia. Eighty-eight per cent of the accessions were Al toxicity tolerant. High Al levels reduced shoot P content by 88% and total dry matter (TDM) by 83%. P addition increased shoot P content and TDM. Rhizobia inoculation increased nodulation by 28–82%, shoot N content by 28–45% and TDM by 15–34% in the low rhizobia density acid soil of Bumala, Kenya. P use efficient accessions had higher nodulation, shoot N content and TDM in the ranges 32–70, 20–52 and 22–36%, respectively, compared to sensitive genotypes. The combination of sesbania accession (SSUG10) and rhizobia strain ASs48 was superior in shoot N accumulation. Inoculation of P use efficient germplasm with acid tolerant rhizobia can improve N-rich biomass accumulation suitable for N replenishment in acid soils.

Economic Returns of the “MBILI” Intercropping Compared to Conventional Systems in Western Kenya

In Kenya, soil acidity is a major contributor to declining soil fertility and 20% of the soils are acidic and are considered to be of low fertility. Most farmers are unaware of the benefits of liming acid soils. A study was carried out during the 2005 and 2006 long rain seasons at Kuinet in Uasin Gishu District of the Rift Valley Province in Kenya to delineate the effects of Minjingu phosphate rock (MPR) and agricultural lime as liming materials on yields of soybeans intercropped with maize. The maize responded to application of soil amendment materials for the first season with the diammonium phosphate and lime (DAPL) treatment giving the highest maize yields of 6.19 t ha–1 compared to the control which gave 1.36 t ha–1. Soybean yields were low in the first season with the DAPL treatment and control treatment giving yields of 0.32 and 0.14 t ha–1, respectively. This, however, changed significantly after the variety was changed in the second season, with yields going up to 0.68 t ha–1 for the triple superphosphate and lime (TSPL) treatment. From the study, it was concluded that there is potential for growing soybean in Uasin Gishu District of Kenya. However, a study and/or research is recommended to screen and identify a suitable variety for increased soybean yields in this district.

Effect of Prep-Pac Application On Soil Properties, Maize, and Legume Yields in a Ferralsol of Western Kenya

In Kenya, smallholder farmers practice maize–bean intercropping. Low nutrient levels in soils result in low yields for both crops. Farmers plant both maize and beans in the same hill or between maize rows, which results in low yields. In the MBILI (Managing Beneficial Interactions for Legume Intercrops) system, the spatial rearrangement gives high legume and cereal yield. An on-farm experiment was carried out in four districts (Bungoma, Siaya, Trans Nzoia, and Uasin Gishu) of western Kenya in a randomized complete block design giving three intercropping systems (MBILI, hill, and conventional), maize and two legumes (bean, soybean, or groundnut) and two fertilizer levels (0 and 150 kg of DAP/ha) with three blocks. The aim was to compare grain yields and economic returns of the MBILI and conventional intercropping systems. Treatment effects were determined by ANOVA analyses using the general linear model of the SAS system. The Bungoma site had the highest groundnut yields for long rains of 2005 and 2006; bean yields under MBILI intercropping (1.4 t/ha). Kitale gave the highest soybean yields of 573 kg/ha from MBILI with fertilizer. The MBILI intercropping gave the highest maize yields (4 t/ha) in all the sites except Sega, while the controls gave low yields (1 t/ha) in all the sites compared to the fertilized intercrops. Economic analyses showed that MBILI gave the highest returns on capital. The distinct finding is that MBILI gave increased maize and legume yields compared to conventional intercropping systems.