Browsing by Author "Shibairo, Solomon I."

Now showing 1 - 20 of 53

Assessment of rainwater retention in agricultural land and crop yield increase due to conservation tillage in Ewaso Ng’iro river basin, Kenya
(2006) Ngigi, Stephen N.; Rockströmb, Johan.; Savenije, Hubert HG.; Seehalak, WK.; Sommanas, W.; Shibairo, Solomon I.; Srinives, P.
Rainwater harvesting and management (RHM) systems are increasingly being recognized as one of the strategies of upgrading rainfed agriculture, especially by smallholder farmers in semi-arid environments. The need to increase crop yields has led to adoption and up-scaling of RHM systems such as conservation tillage and on-farm ponds for micro-irrigation. The paper focuses on conservation tillage, which refers to soil tillage practices that minimize soil manipulation, increase moisture storage and reduce soil and water loss. It aims at conserving rainwater in situ—where it falls within the root-zone. Increased soil moisture storage reduces runoff, which lead to reduction in catchment water yield, and may reduce river flows during the wet and dry seasons. Hence the need to estimate the amount of rainwater retained on croplands and related hydrological impacts. However, estimation of the amount of runoff—additional soil moisture—retained due to in situ RHM systems such as conservation tillage practices is not straightforward. The paper presents an empirical approach based on the analysis of crop yield response to water. The result from empirical approach was compared with field data taken from croplands under traditional and conservation tillage systems in Laikipia district, Kenya. Additional soil moisture retained in the root-zone was reflected in increased maize biomass and grain yields. The empirical approach assumed other soil water balance components such as deep percolation, overall reduction in soil evaporation by conservation tillage over the cropping season and long-term change in soil moisture storage are negligible. The approach is simple compared to other methods based on costly and time consuming field instrumentation and measurements. Field measurements showed that conservation tillage could increase soil moisture storage by 18–50%. Empirical approach yielded values within the same range, i.e. 15–40%. Therefore, empirical approach can be used to estimate the amount of rainwater retained on croplands, and hence proportion of runoff reduced from agricultural catchments.
Botanical composition and selective feeding by goats in the semi-arid Lands of central-eastern Kenya
(2013) Osolo, Nyende Kefa.; Shibairo, Solomon I.; Wakhungu, Jacob W.
Botanical composition of University of Nairobi’s Machang’a Field Station, Mbeere, in the Semi-arid Central-Eastern rangelands of Kenya was inventoried by reconnaissance survey. Relative abundance of the various plant species and ground cover were then established for three seasons: long rains, short rains and dry season. Small East African goats were allowed to graze freely on the range and their selective grazing behavior used to identify the relative preference of plant species. Over one hundred and eighty (180) plant species were identified and recorded. The herbaceous ground cover varied with season and was highest during the long rains study (40.8%) followed by short rains (19.2%) and lowest for dry season (12.6%). Goats showed strong preference for species which were relatively scarce (r<-0.86). Promotion and conservation of the preferred plants was recommended.
Changes in water potential, osmotic potential, and tissue electrolyte leakage during mass loss in carrots stored under different conditions
(Elsevier Science B.V, 2002-08-02) Shibairo, Solomon I.; Upadhyaya, Mahesh K.; Toivonen, Peter M.A
Mass loss, water potential (ψ), osmotic potential (ψπ) and tissue permeability of carrots (Daucus carota L. cv. Eagle) stored for 30 days at 2 °C and 80% relative humidity (RH) (optimal shelf condition (OSC)), 13 °C and 79% RH (common shelf condition (CSC)), or 13 °C and 31% RH (poor shelf condition (PSC)) were monitored. Carrots at PSC lost the most mass followed by those at CSC and OSC. Total water potential (ψ) and osmotic potential (ψπ) of the carrots at CSC and PSC did not change significantly for up to 6 days, but decreased thereafter. No statistically significant change in ψ and ψπ occurred in carrots at OSC. Relative electrolyte leakage (REL) rapidly increased after 12 days at PSC and after 18 days at CSC, at which point mass loss had exceeded 8% of original weight, considered to be a threshold for quality loss. REL of carrots stored at OSC increased only slightly and the mass loss in these carrots did not exceed 8%. Regression analysis showed that mass loss in carrots was consistently associated with REL; changes in ψ and ψπ were associated with mass loss only when carrots were kept at 13 °C. Thus, REL could be a good indicator of mass loss of carrots under a wide range of shelf conditions. The sharp rise in REL at CSC and PSC occurred when the mass loss exceeded 8%.
A comparative evaluation of maturity indices of mango fruits produced in two contrasting agro-ecological zones of Kenya
(Ruforum, 2014) Ambuko, J.; Ouma, L.; Shibairo, Solomon I.; Hutchinson, M.; Njuguna, J.; Owino, WO.
Harvesting mango (Mangifera indica) fruits at the right stage for the destination market and use requires reliable maturity indices. There are various indices that are used to determine harvest maturity for mango fruits. However, differences in cultivars and growing environment affect the reliability of these indices. The present study was conducted to establish maturity indices of two popular mango varieties, ‘Apple’ and ‘Ngowe’. The study was conducted in two contrasting agro-ecological zones (AEZs) of Kenya namely Embu County (a high potential AEZ) and Makueni County (a low potential AEZ). For each variety, the earliest physiological maturity was determined using flesh color. The flesh color was established by cutting the fruits longitudinally to expose the cross sectional view. The earliest physiological maturity (stage 1) was marked as the stage when the flesh was mostly cream and turning yellow at the seed. The number of days after full bloom was matched to this maturity stage (stage 1) and subsequent maturity stages determined at 10-day intervals as stages 2, 3 and 4. For each of the maturity stages, physiological (ethylene evolution and respiration rates); physical (size, peel/flesh firmness and peel/flesh color) and biochemical (Total soluble solids - TSS, Total titratable acidity – TTA and TSS:TTA ratio) maturity indices were determined. The results show that in both varieties (‘Apple’ and ‘Ngowe’) from both locations (Embu and Makueni), respiration rates increased gradually with maturity. ‘Ngowe’ and Makueni fruits registered the higher respiration and ethylene evolution rates compared to ‘Apple’ and Embu fruits for the same maturity stage. As maturation progressed, peel firmness decreased gradually irrespective of variety or production location. In all fruits, flesh color (hue angle) decreased gradually with maturity. Total soluble solids increased while TTA decreased gradually with maturity. Overall, in both varieties, Makueni fruits attained comparable maturity indices to Embu fruits at an earlier stage/date. The results revealed the significant effect of production location on the maturity indices of mango fruits. There is need for additional studies to establish
Comparison of quality attributes of mango fruits produced from two contrasting agro-ecological zones of Kenya
(Ruforum, 2014) Ouma, L.; Ambuko, J.; Shibairo, Solomon I.; Owino, WO.; Hutchinson, M.; Njuguna, J.; Books, Ruforum.; Sheets, Fact.; Oer, Ruforum.; Scarda, Ruforum.
Mango (Mangifera indica) is a tropical fruit adapted to a wide range of agro-ecological conditions. In Kenya, mango fruits are produced across various agro-ecological zones (AEZs); from sub-humid to semi-arid. The diverse production conditions found in these AEZs variably affects fruit growth and subsequently the postharvest qualities. This study was conducted to compare the quality attributes of two mango varieties (‘Apple’ and ‘Ngowe’) produced under two different AEZs. Embu County (a high potential AEZ) and Makueni County (a low potential AEZ) are major mango-producing counties in Kenya. The study was conducted over two seasons between 2013 and 2014. ‘Apple’ and ‘Ngowe’ mango fruits were harvested from the two AEZs at four successive maturity stages; from the earliest physiological maturity (stage 1) to the tree-ripened stage (stage 4). In stage 1 fruits, the flesh was mostly cream and had just started turning yellow around the seed. The subsequent maturity stages were determined at 10-day intervals from stage 1 as stages 2, 3 and 4. For all the maturity stages, initial quality attributes were determined immediately after harvest and the again at a predetermined end stage following ripening at ambient room conditions (Temperature: 25 ± 1 oC and RH: 60 ± 5%). The quality attributes determined include sugars (fructose, glucose, and sucrose), °Brix, %TTA, vitamin C, beta carotene and mineral nutrients (Potassium, Magnesium, Calcium). For sensory evaluation, diced fruits were scored for various attributes including acidity, sweetness, mouth feel, flavor, aroma, color and general acceptability by a panel of 33 untrained panelists. For all the parameters evaluated, there was significant interaction (Pd”0.05) between maturity stage, variety and AEZ. Levels of TTA decreased gradually with the stage of maturity irrespective of variety and AEZ. Overall, Embu fruits had higher initial TTA levels for all maturity stages. Although Apple fruits (all stages) had higher initial TTA, at the end of ripening TTA levels were relatively lower compared to Ngowe. Initial beta carotene levels increased while vitamin C levels decreased with maturity stage. Significantly higher beta carotene and vitamin C levels (initial and end stage) were observed in Makueni fruits. Initial and end stage Ca, Mg and K levels decreased with maturity stage, irrespective of variety or AEZ. Stage 1 and 2 fruits retained the highest Ca and Mg levels at the end stage. The highest sugar levels and end stage 0brix levels were observed in stage 4 fruits (regardless of AEZ and variety). Overall, Makueni fruits had relatively higher end stage 0brix levels compared to Embu fruits. In ‘apple’, Makueni fruits scored higher than Embu fruits for all the sensory attributes. On the contrary in ‘Ngowe’,
Cyanogenic content, aflatoxin level and quality of dried cassava chips and flour sold in Nairobi and coastal regions of Kenya
(KALRO, 2015-12-20) Gacheru, Patrick Kamau; Abong, George Ooko; Okoth, Michael Wandayi; Lamuka, Peter Obimbo; Shibairo, Solomon I.; Katama, Christine Masha
Cassava is a staple food for approximately 800 million people in the world. However, it poses food safety risks to the consumers due to naturally occurring cyanogenic glucosides. Thirty six samples of cassava products from Nairobi and Mombasa markets were evaluated for hydrogen cyanide (HCN), aflatoxin, moisture content, and colour. The HCN content was in the range 27.20- 42.92 mg/kg and 21.45-37.77 mg/kg in cassava chips; 21.53-64.63 mg/kg and 21.70-70.03 mg/kg in flour from Nairobi and Mombasa respectively. The HCN was significantly different (p≤0.05) among samples in both the dried cassava chips and cassava flour. Aflatoxin levels detected in two flour samples from Nairobi were 6.60 and 8.89 µg/kg respectively, and one sample from Mombasa; 2.84 µg/kg. Moisture content was in the range of 8.62-9.98% and 8.85-11.57% in cassava chips; 8.50- 12.51% and 7.30-11.0% in cassava flour samples from Nairobi and Mombasa, respectively. The L* values were in the range of 83.9-92.0 and 69.0-81.7 and the colour difference from the standard white paper (DE*) were in the range of 14.5-22.7 and 25.6-37.1 in cassava chips samples from Nairobi and Mombasa markets respectively indicating dried cassava chips sold in the markets were less white. The L* values for cassava flour was in the range of 95.3-100.0 and 94.7-100.0 with DE* of 4.6-9.6 and 0.9-11.5 for Nairobi and Mombasa markets respectively indicating very white flours were sold in the market. These results show that the flour in the market may be of good aesthetic quality but unsafe for consumption. Effect of processing on safety could be evaluated.
Effect of accel (gibberellins (ga4+7) + benzyladenine) on the shelf life of French beans, phaseolus vulgaris L.
(2003) Ambuko, J.; Emong'or, E.V.; Shibairo, Solomon I.; Chemining'wa, G.N.
To determine the effects of Accel on the shelf life of French beans, Phaseolus vulgaris L. variety Monel, two field experiments were conducted at the University of Nairobi’s Kabete Field Station for two seasons. Accel was sprayed at 12.5, 25.0, 37.5 and 50.0 mg/litre to the bean plants to run off just before flowering. The field experiments were followed by laboratory experiments where the effect of Accel on water content and moisture loss by the French bean pods after storage was determined. Chlorophyll content of fresh pods at harvest and that retained by the pods after eight days of storage was also determined. Increase in Accel concentration led to a linear increase in the water content of pods. Accel reduced moisture loss by the pods thereby reducing the extend of wilting. A pplication of Accel significantly increased fresh pod chlorophyll content and enhanced chlorophyll retention in the pods after storage. The response to increasing Accel concentration was linear.
Effect of levels and timing of application of gibberellic acid on growth and yield components of common beans
(African Crop Science Society, 2003-09-15) Ngatia, T.M.; Shibairo, Solomon I.; Emongor, V.E.; Obukosia, S.D.
This study was conducted to determine the effect of levels and timing of application of gibberellic acid (GA3) on growth and yield components of common beans (Phaseolus vulgaris L.). Experiments were conducted at the Field Station Farm at the Faculty of Agriculture, University of Nairobi, Kenya during 1997 and 1998. "Mwezi moja" bean cultivar was used in study. Gibberellic acid (GA3) was sprayed at 0, 2.5, 5.0 and 7.5 mg l-1 to whole bean plants at 7, 14 or 28 days after emergence (DAE). The effect of GA3 and timing of application on growth, yield and yield components was significant (P<0.05). Applications of GA3 led to increased plant height, leaf area index (LAI), fractional solar radiation interception, root, shoot and the total dry mass. It also increased yield per plant, pods per plant, 100-seed mass and harvest index. The highest seed yields were equivallent to 1854 kg ha-1 in 1997 and 5890 kg ha-1 in 1998. These yields are high as compared to average national yields of 500 kg ha-1. Significant differences in the parameters measured were generally observed at 14 DAE in GA3 treated plants.
Effect of Modified Atmosphere Packaging (MAP) on the Shelf Life and Postharvest Quality of Purple Passion Fruit (Passiflora Edulis Sims)
(2014-07-03) Yumbya, Peninah; Ambuko, Jane; Shibairo, Solomon I.; Owino, Willis
Passion fruit (Passiflora edulis Sims) being highly perishable is susceptible to rapid water loss after harvest leading to diminished quality. This study evaluated the efficacy of activebag® which is a new modified atmosphere packaging (MAP) product in the Kenyan market. Fruits harvested at 60-65 and 75-80 days after anthesis were either packaged in activebag® or ordinary polyethene bags and allowed to ripen under ambient room conditions. MAP maintained the quality of fruits harvested at both stages of maturity and prolonged their shelf life by at least 14 days compared to the unpackaged controls. Packaging significantly slowed weight loss, which was lower at 7% compared to the unpackaged controls that lost up to 26% of the weight. Both MAP packages reduced ethylene production and respiration rate and slowed other physicochemical changes associated with passion fruit ripening. Although the ordinary polythene bag packaging prolonged the fruits’ shelf life compared to unpackaged control, their positive effect was negated by high incidence of rotting evident after 14 days of storage. These results indicate that use of activebag® can prolong the shelf life by maintaining quality attributes and external appearance of purple passion fruits and hence extend their marketing period.
Effect of organic and in organic fertilisers on yield and quality of amaranth in sub-Saharan Africa
(African crop science society, 2011-10) Onyango, CM.; Harbinson, J.; Shibairo, Solomon I.; Imungi, JK.
This study was designed to evaluate the influence of manure and mineral fertilization on yield, Kjeldahl nitrogen (as protein equivalents), Vitamin C and nitrate accumulation in Amaranthus hypochondriacus. The vegetables were produced in field trials, set up in the University of Nairobi, Kenya, during the long rains period between March and May in 2007 and 2008 using diammonium phosphate (DAP; 20, 40 and 60 kg N ha-1) and manure; 40 kg N kg ha-1,) and the yield, Kjeldahl nitrogen (K-N; a proxy for protein content), vitamin C and nitrate levels were measured. The manure treatment produced little increase in productivity though it increased K-N levels. The DAP treatments produced increases in yield, but these saturated at 40 kg N ha -1. The K-N content of the leaves was high, ranging from 2.5 % to just over 4 %, and, broadly, increased with fertiliser application though the variation between the treatments was lower than that for yields. Nitrate levels, however, also increased with DAP fertilisation, resulting in an increase in the nitrate:K-N at high DAP applications, especially in younger plants. There were no clear correlations between ascorbic acid content and K-N. Nonetheless, the plants grown under different fertilisation regimes can be placed into three broad groups; those characterised with low to moderate K-N contents and low to high ascorbic acid contents, moderate to high K-N and low to high ascorbic acid content, and lastly high K-N and low ascorbic contents. Therefore, the growth environment of amaranth, can have a major impact not only on the productivity of the crop but its nutritional value. In this respect the mineral nutrient supply to the crop is of particular importance.
Effect of packaging material on shelf Life and quality of ware potato tubers stored at ambient tropical temperatures
(Springer Netherlands, 2018-09-01) Nyankanga, Richard Ombui.; Murigi, Winnie Wanjiku.; Shibairo, Solomon I.
The effect of seven packaging materials (transparent perforated and non-perforated high-density polyethylene (HDPE) bags, black perforated and non-perforated low-density polyethylene (LDPE) bags, nylon gunny sacks, khaki bags and net bags) on post-harvest quality of tubers from three potato cultivars was evaluated. Data were collected on time and percentage of sprouting, weight loss rates and percentage tubers with greening and rotting. Packaging significantly reduced weight loss and rate of tuber greening but increased the rate of sprouting and decay incidences. Non-perforated PE bags were the most effective in reducing weight losses, recording losses of 0.7 to 0.9% after 32 days in storage while unpackaged tubers had weight losses of 11 to 12%. Tuber rotting was highest (60 to 66% of the tubers) in non-perforated PE bags. Greening was faster in non-packaged tubers recording 55 to 100% after 2 weeks in storage and showed high cultivar differences, but did not occur in black bags, whether perforated or non-perforated. Sprouting was complete by week 3 in all tubers packaged in non-perforated HDPE bags irrespective of cultivar. Although the non-perforated HDPE bag packaging prevented weight loss, its positive effect was counteracted by the high incidence of rotting and sprouting. Amongst the different materials evaluated, perforated low-density black PE bags were the best method for ware potato packaging due to low sprouting, reduced weight loss, low rate of tuber greening and reduced rate of tuber decay compared to other packaging materials. The study also indicated that the interaction between cultivars, packaging and storage period also affected shelf life of ware potatoes under ambient tropical conditions.
Effect of packaging materials on weight loss and nutrient quality changes of rechanded sweet potatoes (Ipomoea batatas Poir) during short-term storage
(2004) Shibairo, Solomon I.; Shikuku, CA.; Imungi, JK.; Hagenimana, V.
The effects of packaging materials on weight loss and nutrient quality changes of recharged submerged in clean tap water) sweet potatoes (Ipomoea batatas Poir) roots during storage were determined. Sweet potatoes from two genotypes, ‘KEMB 10\' and ‘Yanshu\' were recharged for 14 hours and packaged in perforated polyethylene bags (0.02 mm), Kraft paper bags (0.025 mm) and nylon gunnysacks, with roots placed on open plate as control. The packages were then stored at prevailing ambient conditions (23 ± 2 oC, 77.5 ± 5.5 % relative humidity (RH)) for 21 days. During storage the sweet potatoes\' change in weight was determined every 3 days. Change in reduced ascorbic acid, ß-carotene, total sugars and total soluble solids contents were determined every 7 days. There was a significant (p ≤ 0.05) weight loss as well as reduced ascorbic acid loss, but total sugars and ß-carotene contents increased during storage. Although total sugars showed an apparent gradual increase in all packages and genotypes during storage, the increase was not significant (p ≤ 0.05). Perforated polyethylene bags significantly (p ≤ 0.05) prevented weight loss (up to 1.8 %) as well as allowed for the most retention in reduced ascorbic acid (13.45 g/100 g fresh weight), and increase in ß-carotene (4.9 mg/100 g fresh weight) and total sugar (6.4 g/100 g dry weight) contents than Kraft paper bags and nylon gunnysacks. Roots packaged in Kraft paper bags were not different in weight and nutrient quality changes from those packaged in nylon gunnysacks. The control sweet potatoes always showed the highest losses in weight (up to 27.8 %) and nutrient quality. Packaging materials did not affect total soluble solids content during storage. The results show that packaging in perforated polyethylene bags can improve shelf life of recharged sweet potatoes by 14 days.Keywords: Ipomoea batatas; packaging; weight loss
Effect of Rhizobium inoculation and nitrogen fertilizer application on growth, nodulation and yield of two garden pea genotypes.
(FACT Limited, 2012) Ngeno, J.; Chemining’wa, G.N.; Muthomi, J.W.; Shibairo, Solomon I.
Nitrogen is the most limiting nutrient in smallholder garden pea farms in Kenya and can be corrected by application of inorganic fertilizers and Rhizobium inoculation. A study was conducted to compare the effects of Rhizobium inoculation and nitrogen fertilizer application on nodulation and yield of two garden pea varieties grown for local (variety Plum) and export (variety Ambassador) markets. Field experiments were conducted at University of Nairobi's Field station in 2007 short and long rains. Varieties Plum and Ambassador were either inoculated with a commercial strain of Rhizobium leguminosarum bv. viciae, supplied with 30 or 60 kg N ha-1 or without any treatment. Inoculation and N-fertilizer enhanced shoot dry matter, but had no effect on grain yield. Plots receiving 60 kg N ha-1 intercepted more photosynthetically active radiation than non-treated control plots. Rhizobium inoculation increased number of active nodules and nodule dry matter. Plum variety accumulated more nodule and shoot biomass than Ambassador. Variety Ambassador had longer and more seeds per pod than Plum while the converse was the case in number of pods plant-1. Nodulation observed in control plots indicated that native pea rhizobia in Kabete soils are compatible with Plum and Ambassador garden pea varieties. Rhizobia inoculation of garden pea can yield similar shoot biomass as nitrogen application. Nitrogen fertilizer increased shoot dry matter, leaf area index and PAR interception by garden pea. Increases in above ground biomass and nodulation due to rhizobia inoculation and nitrogen fertilizer application were not translated into increased pod and grain yield. Growth and nodulation responses to inoculation and nitrogen fertilization were dependent on the garden pea genotype, hence the need to investigate the differential response of Plum and Ambassador. It is suggested that a study be conducted to determine the effect of Rhizobium inoculation and nitrogen fertilization on a broad range of locally grown garden pea genotypes.
Effect of source, time and method of nitrogen application on growth and yield components of potato in Kenya
(2000) Mburu, Mary WK.; Gathungu, GK.; Shibairo, Solomon I.; Githiri, SM.; Ojiambo, PS.; Kidanemariam, HM.
The effect of different sources of Nitrogen (N), time and method of application on growth and development of potato was investigated over two seasons using the cultivar Dutch Robjyn. The three sources of nitrogen (Calcium Ammonium Nitrate (CAN, 26% N); Urea (46% N) and Ammonium Sulphate Nitrate (ASN, 27%N)] constituted the main plot treatments, and time [early application, split application (half of the fertiliser at planting and half applied 5 weeks after emergence), and late application (5 weeks after emergence)] and method of application (placement and broadcast within the furrow) constituted the subplots treatments. Early application of N followed by split applied fertiliser led to a fast early growth (shoot, tuber, root and total dry matter, Leaf Area Index (LAI) development, and plant height) particularly where CAN or ASN was applied. Late N application enhanced growth of the shoots (leaves and plant height) later in the growth season particularly with Urea. Broadcast or placement of N in the furrow had no significant effect (P<0.05) on growth and development. There was significant difference (P<0.05) between the times of application of N. Early application of N followed by split applied fertiliser showed the greatest tuber yield. Late application of fertiliser had the lowest tuber yield but the highest total N accumulation in both leaves and tubers. Broadcasting and placement of N in furrows had no significant effect on nitrogen content, tuber numbers and yield/plant. CAN followed by ASN promoted tuber growth and yield more than Urea. CAN, should thus be applied early in the growth season either as a broadcast or placement in the furrow and application of Urea is less beneficial since it is amenable to leaching and volatilisation.
Effectiveness of indigenous pea rhizobia (Rhizobium leguminosarum bv. viciae) in cultivated soils of central Kenya
(J. Appl. Biosci., 2012-09-30) Chemining’wa, George N.; Ngeno, J.; Muthomi, J.W; Shibairo, Solomon I.
Objective: This paper reports on a study conducted to determine the effectiveness of pea rhizobia (Rhizobium leguminosarum bv. viciae) resident in Central Kenyan soils. Methodology and results: Garden pea (Pisum sativum cv. Plum) grown in pots containing soils collected from 26 sites, with and without a history of pea cultivation, in central Kenya was inoculated with a commercial rhizobial strain, supplied with 74 mg N pot-1, or did not receive any treatment (control). Rhizobial inoculation enhanced pea nodule numbers in soils from some sites that had no history of pea cultivation. Nitrogen fertilizer depressed pea nodulation in soil samples from all sites. Most abundant active and total nodules (20 and 22 nodules plant -1) were recorded in sites with adequate soil N, high organic carbon and history of pea cultivation In many cases, plants in untreated soils had a high nodule number and accumulated more shoot biomass than plants growing in inoculated or nitrogen supplied soil. This confirmed the N2 fixation efficiency of indigenous pea rhizobia strains. Plants that had poor nodule formation were those growing in soils from a site in Nyeri that was low in soil N and organic carbon. . Conclusion and application: Most soils in Central Kenya have abundant and efficient native strains of pea rhizobia irrespective of pea cultivation history. In some sites, indigenous rhizobia out-performed the commercial inoculant strain. Thus, it is advisable to screen indigenous pea rhizobia strains in the target sites for N2 fixation efficiency with the objective of making more effective inoculants. Improvement in soil organic carbon in Central Kenya can enhance the benefits accruable from pea N2 fixation. A similar study involving a broad range of pea genotypes and strains of Rhizobium leguminosarum bv. viciae is recommended.
Effects of early and late harvest on agronomic performance and stability of late blight resistant (R-gene Free) Potato genotypes
(Korean Society of Crop Science and Springer., 2014-06-01) Nyankanga, Richard.; Kiplagat, Willy.; Narla, Rama.; Shibairo, Solomon I.; Kabira, Jackson.; Landeo, Juan.; Olanya, Modesto.
Late blight is an important constraint to potato production and genotype resistance is an effective disease control mesure. Ten late blight resistant potato genotypes (R-gene free) were assessed for yield performance and stability at early (90 days) and late harvest (120 days) at two locations in Kenya during two years. Significant differences (P < 0.05) in area under disease progress curves (AUDPC) were detected among potato genotypes. Resistant genotypes free of R-genes had significantly (P < 0.05) higher yield at late than early harvest, perhaps due to increased tuber bulking period. The rank of genotypes for AUDPC, late blight resistance, and tuber yield varied across seasons and locations (environment). Additive main effects and multiplicative interaction (AMMI) analysis of tuber yield and late blight resistance resulted in significant (P < 0.05) effects of genotypes (G) and environments (E). The proportion of genotypic variance was larger than the environmental variance and the G × E interactions. For tuber yield, the G, E, and G × E interactions accounted for 42.9, 39.6 and 17.5%; and 53.4, 29.7, and 16.9% at early and late harvests, respectively. For AUDPC, G, E, and G × E accounted for 80.2, 5.0, and 14.8%; as well as 82.3, 4.6, and 13% for early and late harvests, respectively. The resistance of potato genotypes without R-genes varied. Selective deployment of resistant genotypes can improve potato tuber yield.
Effects of ethephon on the growth, yield and yield components of beans (Phaseolus vulgaris L.)
(JKUAT, 2003) Ngatia, M.; Shibairo, Solomon I.; Emongor, V.E.; Kimenju, J.W.
Two experiments to determine the effects of timing and levels of application of ethephon on the growth and yield of common bean (Phaseolus vulgaris L). were conducted. Bean cultivar \'Mwezi moja\' was used. Four levels of ethephon (0, 100, 200 and 300 mg/l) were sprayed to the plants at 7, 14 or at 28 days after emergence (DAE). Application of ethephon at all the three timings led to reduced plant height. Application of ethephon at 28 DAE reduced the leaf area index (LAI), fractional solar radiation interception, shoot dry mass and total dry mass. Root dry mass was not affected by ethephon application. Application of ethephon particularly at 28 DAE reduced yield and number of pods per plant. Application at 7 and 14 DAE in experiment 1 and 28 DAE in both experiments increased the number of seeds per pod. Ethephon application at 14 DAE increased the 100-seed mass in experiment 1 but reduced it in experiment 2. Most reduction in 100-seed mass occurred with application at 28 DAE. The harvest indices were reduced by application of ethephon at 28 DAE in both experiments and 14 DAE in experiment 1. It was concluded that ethephon (ethylene) application did not have any beneficial effects in bean production.
Effects of moisture loss on water potential components and tissue deterioration in carrots during Short-term storage
(American society for horticultural science, 1995-07-01) Shibairo, Solomon I.; Upadhyaya, MK.; Toivonen, PMA.
Studies were carried out to understand the effects of moisture loss on water potential and root deterioration in carrot (Daucus carota L. `Eagle') roots during short-term storage. The roots were stored at various temperatures and relative humidities (RH) to provide 0.7 (low), 3 (medium), and 9 mbars (high) of water vapor pressure deficit (WVPD). Carrots at high WVPD lost the most weight, followed by those at medium and lowest WVPD. Water potential and osmotic potential of the carrot tissue at high WVPD did not change significantly up to 6 days, but decreased thereafter. There was no change in water potential and osmotic potential for carrots at medium and low WVPD. A significant quadratic relationship (P = 0.05, r = –0.764) between water potential and carrot root weight loss was observed. Relative electrolyte leakage increased over time in carrots at the high WVPD.
Effects of Nitrogen and Phosphorus fertiliser on growth and yield of ironweed (vernoniagalamesis)
(2003) Mburu, Mary W. K.; Mati, G. N.; Kurji, P. N.; Shibairo, Solomon I.
Ironweed (Vernonia galamensis) is a promising new crop for industrial oil but information on its response to ferfiliser is scanty. A field experiment was conducted at the University of Nairobi Field Station farm during 2 seasons (January to May 1998, season 1 and March to August 1998, season 2) to determine the effects of nitrogen (N) and phosphorus (P) fertiliser rates on growth, photosynthetically active radiation (PAR) interception and seed yield of 2 Vernonia galamensis cultivars (ethiopica and gibbosa). N was applied at 0, 75 and 150 kg Nlha, and P at 0, 45 and 90 kg P2O5s/ha. The experiment was a 2 x 3 x 3 factorial laid out in a randomized complete block design with 3 replications, N and P application significantly increased total dry matter . (TDM), photosynthetically active radiation . (PAR) interception and leaf area index (LAI) of both varieties in late vegetative and reproductive stages. Gibbosa had consistently higher TDM-LAI, PAR and was taller compared to Ethiopica throughout the growing season.Average seed' yield of gibbosa was 2.3 times higher than that of ethiopica in both experiments. The highest TDM, LAI and seed yields were obtained at the highest N and P levels. Gibbosa had a significantly higher number of capsules/plant but a lower harvest index CHI) compared to ethiopica.
Effects of phosphorous on growth and yield of snowpeas (pisum sativum var. oregon sugar pod ii)
(2015-07-31) Mburu, Mary W.K.; Njoroge, Patrick K.; Shibairo, Solomon I.; Githiri, S.M.
Two field experiments were carried out concurrently at the Faculty of Agriculture, Field station farm, University of Nairobi in March-July 2000 (season I) and June-September 2000 (season II) to determine the effect of application of different levels of phosphorous (P) fertilizer on growth and yield of snowpea (Pisum sativum L. var. Oregon sugar pod II). The experiments were laid out in a complete randomized block design with three replicates. Four levels of P (0, 57, 114 and 171 kg P2O5 ha-1) were applied as TSP (46% P2O5) at planting. Plant heights were measured at 31,38,45,58,71,84 and 97 DAS. Leaf area index and above- ground dry mass were determined at 29, 43, 63, 77 and 94 DAS. Harvesting of pods was done at 68, 72, 75, 79, 82, 86, 89, 93, 96 and 100 DAS. P fertilization resulted in significant (P  0.05) increases in plant height, leaf area index, and total above ground dry matter accumulation in both seasons. Number of pods plant-1 showed a quadratic trend with increasing P at 68, 89 and 93 DAS in season I. Linear and quadratic increases in number of pods plant-1 were observed at 96 DAS and on total number of pods plant-1. At 100 DAS, only linear increase was observed. Pod dry mass plant-1 showed a quadratic increase at 68, 89, 93 and 96 DAS. At 100 DAS, linear increase in pod dry mass plant-1 was observed. Linear and quadratic increases were observed in total pod dry mass plant-1. P application did not affect both the number of pods and pod dry mass plant-1 in season II probably because of the low amount of rainfall. Application of 57 kg P2O5 ha-1 resulted in dry pod yields of up to 9.75 tons ha-1 which is higher than the national dry mass averages of 5 to 6 tons ha-1. It is therefore recommended that judicious levels of P be applied for growth of snowpeas.