Soil nutrient content, soil moisture and yield of Katumani maize in a semi-arid area of Kenya

Many farmers in Kenya’s semi arid lands cannot afford to purchase inorganic fertilisers to improve their crop yields. They thus rely on traditional agronomic practices such as addition of crop residues, animal manures or intercrops of cereals and legumes. This study investigated soil parameters and their influence on yield. It was carried out at the University of Nairobi’s Dryland, Research and Utilisation Station located at Kibwezi. Soil parameters measured included soil organic carbon, total soil nitrogen, available phosphorus, soil moisture and soil texture and nitrogen mineralization rates. There was significant correlation (p<0.05) in the growing seasons, between soil moisture and soil organic carbon (r = 0.66, 0.81 and 0.65 for seasons 1, 2 and 3 respectively) as well as total soil nitrogen (r = 0.73, 0.79 and 0.70 for seasons 1, 2 and 3 respectively) and available phosphorus (r = 0.55 for season 1). Where rainfall was low, maize yield correlated negatively (p<0.05) with percent clay content (r = -0.4) in season one and showed no significant correlation (r=0.21) in season 3. Where rainfall amounts were high, (as in season 2), the correlation was significant (r = 0.75). Nitrogen mineralization rate did not seem to have a direct influence on yield but its effects were modified by soil moisture, soil texture and carbon to nitrogen ratios of the soil. Overall the organic inputs seemed to have minimal impact on yield though goat manure and pigeon pea intercropping had a melioration effect on the soil.Keywords: Soil nutrients, maize yield, semi-arid, Keny

Leaf stomata conductance, leaf water potential and soil water status in Panicum maximum jacq. in disturbed and non‐disturbed microsites in a semi‐arid ecosystem in kenya

Tropical semi-arid ecosystems are intricate ecosystems characterized byalternating dry-wet cycles. The question of how trees and grasses coexist under a considerable range of environmental and management conditions has been referred to as the "savanna problem" The practical significance of understanding the dynamics of natural ecosystems in relation to  disturbances induced by herbivory, changing land use patterns or climate change is increasingly being recognized. Natural resource conservationists, range managers, and other custodians of natural resources require concrete information bases for land use policy formulations and as a means of regulating land use systems for sustainable resource use and development. An experiment using a randomised complete block design was set up to measure the effects of induced disturbances on ecosystem components and concomitant plant physiological responses. Analysis ofvariance techniques were used to determine the presence or absence of significant treatment effects. Disturbed micro]sites (manipulated treatments where Acacia tortilis trees were removed) demonstrated contrasting results compared to the non-disturbed micro-sites (Acacia tortilis trees left intact).The disturbed sites had less average moisture content in the 10cm soil profile (14.4%) than the nondisturbed sites(18.8%). Panicum maximum had an average stomata conductanceof a magnitude of 0.65cms-1(270mmolm-2 s-1) for the disturbed microsites and 0.75cms-1(312mmolm-2s-1) for the non-disturbed sites. There were no significant treatment effects in transpiration rates and leaf water potential of Panicum maximum in the disturbed and non-disturbed sites. This analysis demonstrates that long term changes in  microenvironmental conditions of soil and plant water status due to tree removal is likely to cause shifts in botanical composition of graminoid species with direct implications on nitrogen sequestration, species biodiversity, and productivity.Key words: Panicum maximum, semi-arid ecosystems, soil water status, stomata conductance, tree-grass interactions, micro-environmental fluxe

Production and decomposition of plant litter in an arid rangeland of Kenya

Data on litter production and decomposition in an arid rangeland in Kenya was collected over a two-year period. Litter sampling was carried out at monthly intervals using a rectangular 0.25m-2 quadrat frame. Litter within the quadrats was handpicked and washed with running water to get rid of soil particles, dried, and weighed. Weights were expressed on organic matter basis. Monthly litter production ranged from 31.4g m-2 to 130.0g m-2. Mean monthly yield was 92.5 ± 26g m-2, with a 28% coefficient of variation. There was no significant difference (p>0.01) in litter yield between 1992 and 1993. Rate of decomposition for aboveground material ranged from 0.005g g-1 day-1 to 0.084g g-1 day-1. The mean annual rate of decomposition was 0.026g g-1 day-1. Belowground plant material rates of decomposition spread from 0.009g g-1 day-1 to 0.062g g-1 day-1, with a mean annual rate of 0.041g g-1 day-1. Belowground material consistently decomposed faster than aboveground material. Peaks in both aboveground and belowground material decomposition rates coincided with rainfall peaks. Overall, in this arid environment, litter production and decomposition is pulsed in nature, and trends are closely related to rainfall occurrence. Moisture is thus a limiting factor both to the production and decomposition of litter. Belowground litter plays a significant role in nutrient cycling. Keywords: dead herbage yield; dryland ecosystem; ecosystem function; nutrient cycling African Journal of Range & Forage Science 2001, 18(2&3): 125-12

Soil nutrient content, soil moisture and yield of Katumani maize in a semi-arid area of Kenya

Many farmers in Kenya’s semi arid lands cannot afford to purchase inorganic fertilisers to improve their crop yields. They thus rely on traditional agronomic practices such as addition of crop residues, animal manures or intercrops of cereals and legumes. This study investigated soil parameters and their influence on yield. It was carried out at the University of Nairobi’s Dryland, Research and Utilisation Station located at Kibwezi. Soil parameters measured included soil organic carbon, total soil nitrogen, available phosphorus, soil moisture and soil texture and nitrogen mineralization rates. There was significant correlation (p<0.05) in the growing seasons, between soil moisture and soil organic carbon (r = 0.66, 0.81 and 0.65 for seasons 1, 2 and 3 respectively) as well as total soil nitrogen (r = 0.73, 0.79 and 0.70 for seasons 1, 2 and 3 respectively) and available phosphorus (r = 0.55 for season 1). Where rainfall was low, maize yield correlated negatively (p<0.05) with percent clay content (r = -0.4) in season one and showed no significant correlation (r=0.21) in season 3. Where rainfall amounts were high, (as in season 2), the correlation was significant (r = 0.75). Nitrogen mineralization rate did not seem to have a direct influence on yield but its effects were modified by soil moisture, soil texture and carbon to nitrogen ratios of the soil. Overall the organic inputs seemed to have minimal impact on yield though goat manure and pigeon pea intercropping had a melioration effect on the soil

Dispersal distance of rice (Oryza Sativa L.) pollen at the Tana River delta in the coast province, Kenya

Rice is a staple food in Kenya and its production needs to be increased. Genetically modified (GM) rice may be a solution, but before it can be introduced, potential ecological impacts, such as pollen mediated gene flow from GM rice to non-GM rice or to its wild indigenous relatives, need to be understood. Pollen dispersal in rice (Oryza sativa) was studied in the Tana River district in the coast province of Kenya. O. sativa seedlings were planted in a 50 m diameter circular experimental design. Pollen traps (glass slides coated by vaseline attached to a board) were used to measure pollen flow at 2 heights and at increasing distances from the source plot. Pollen dispersal decreased rapidly withincreasing distance from the pollen source up to 250 m, no pollen was found at 300 m. There was a significant (P 0.05) in pollen count between upper and lower pollen traps. The highest daily pollen count was observed between 11:00 am and 12:00 noon, and at a narrow range of temperatures 28 ± 2ºC. On the basis of these data, an adequate isolation distance of more than 250 m should be considered to minimize chances of gene flow from transgenic rice to conventional or wild rices

Abiotic and herbaceous vegetational characteristics of an arid rangeland in Kenya

A two-year study was conducted with an overall objective of characterising the structure and function of an arid rangeland in Kenya. A plot measuring 100 x 100m was used for this study. Data on rainfall and temperature were recorded at the plot site whereas data on evaporation rates and relative humidity were obtained from the meteorological office near the study site. Herbaceous aboveground material was sampled at monthly intervals using a rectangular 0.25m2 quadrat frame. Clipped material was separated by species and classified dead or live by physical examination. A 5cm diameter metal soil corer was used to sample belowground plant material, at monthly intervals. The sampled material was washed with running water over 2mm sieves and classified dead or live using the vital staining technique. All weights and calculations were based on organic weight. Total aboveground standing crop ranged from 84.6g m-2 to 295.4g m-2, with a mean of 162.3 60.6g m-2. Mean monthly aboveground standing crop for 1992 and 1993 was 142.8 53.8 and 178.5 63.3g m-2 respectively. The two values were significantly different (p0.01) in the mean belowground dead material yield between 1992 and 1993. In 1992, annual NPP was 439.2g m-2, giving a net primary productivity of 1.22g m-2day-1. Monthly NPP ranged from 17.2g m-2 to 90.1g m-2. In 1993, annual NPP was 944.5g m-2, equivalent to a net primary productivity of 2.62g m-2day-1. Monthly NPP was between 27.4g m-2 and 548.6g m-2. Over the 19921993 period, NPP was 1 383.7g m-2, equivalent to a productivity of 1.92g m-2day-1. Trends in monthly NPP closely followed the trend in rainfall. On the whole, herbaceous vegetation production and productivity were episodic in nature and closely linked to rainfall. The high primary productivity puts arid and semi-arid rangelands under sharp focus as CO2 sinks, whose role in the amelioration of greenhouse effect could be more important than is currently appreciated. Keywords: climatic elements; aboveground biomass; belowground biomass; primary productivity African Journal of Range & Forage Science 2001, 18(2&3): 117-12

Morphological and RAPD-marker characterization of Melia volkensii (Gürke) in vitro plants regenerated via direct and indirect somatic embryogenesis

Somaclonal variation induced in vitro during tissue culture can be a problem in clonal micropropagation of elite plants. This study investigated the extent of morphological and genetic similarity or dissimilarity between Melia volkensii in vitro plants (somatic seedlings) obtained via somatic embryogenesis and normal seedlings. Comparisons were made between in vitro plants regenerated directly from cotyledon explants, indirectly from zygotic embryos and normal seedlings of the same parent trees. Regeneration was achieved using half MS medium supplemented with 0.05 mg/l thidiazuron. Shoots were elongated in half MS with 0.1 mg/l BAP plus 0.01 mg/l IAA then rooted in half MS with 0.1 mg/l IBA and 0.1 mg/l NAA. Six morphometric and five meristic characters were used for the morphological characterization. PCR-RAPD markers were used for assessment of genetic similarity or distance. Multivariate analysis using principal coordinates, cluster analysis, analysis of similarities (Anosim) and similarity percentages analysis (SIMPER) revealed significant dissimilarities (p&lt; 0.0001) in morphometric and meristic characters between the in vitro plants and normal seedlings. However, significant similarity (p&lt;0.01) was observed in the RAPD-genic characters of the in vitro plants and normal seedlings. Out of six morphometric traits, taproot length, internode length and shoot height were the most important sources of dissimilarity, cumulatively accounting for 72.37% of overall morphometric dissimilarity. Number of lateral roots was the single most important source of meristic dissimilarity, with 77.02% contribution. Plants regenerated directly from cotyledons were more similar to the normal seedlings in morphological and RAPD-marker characters than those regenerated indirectly from zygotic embryos. This study paves the way for identification of trait-specific RAPD markers for further characterization through sequence-characterized amplified regions (SCARs).  Key words: Morphometric, meristic, PCR-RAPD, Melia volkensii, tissue culture, somaclonal variation

Patterns of seed dispersal and establishment of the invader Prosopis juliflora in the upper floodplain of Tana River, Kenya

Invasive species in Africa have important impacts on food security and biodiversity conservation. African floodplains in arid areas are critical wildlife habitats in addition to crop production and dry season livestock grazing. The study aimed to understand the patterns of spread of the invader Prosopis juliflora in a typical African floodplain characterised by both multiple dispersers and habitats. Data was collected on faecal seed density, establishment and vegetation composition, and subjected to non-parametric tests and regression analysis. The results showed that both livestock and wildlife species played a critical role in dispersal of Prosopis juliflora, especially yellow baboons (Papio cynocephalus), bush pigs (Potamochoerus larvatus), donkeys and goats. Habitat preference of wildlife dispersers and livestock herding patterns influenced the spatial pattern of invader seed influx. Establishment of Prosopis juliflora was enhanced by ecological disturbance such as in rested crop fields and habitats outside conservation areas as compared to those inside. Establishment was also higher inside the floodplain than outside probably due to higher seasonal soil resources. Lastly, indigenous woody species diversity declined significantly as the density of Prosopis juliflora increased. We conclude that patterns of spread of Prosopis juliflora were related to ecological disturbances, type of disperser and flooplain effect.African Journal of Range & Forage Science 2011, 28(1): 35–4

KEYWORDS Seed-borne Fungal infections Germination mortality Melia volkensii Seedlings INCIDENCE AND CONTROL OF SEED-BORNE FUNGAL INFECTIONS ASSOCIATED WITH POST-GERMINATION MORTALITY IN SEEDLINGS OF Melia volkensii GURKE

ABSTRACT A laboratory study was carried out at the School of Biological Sciences, Chiromo Campus, University of Nairobi, for identification of seed-borne fungi that emerge during germination of M. volkensii seeds. The study sought to determine the incidence, pathological symptoms and effects of the fungi on postgermination survival of seedlings. Mature seeds collected from wild trees in three agro-climatic zones in semi arid eastern Kenya were scarified by nipping and slitting of the testa and divided into two groups. The treatment group received a single pulse pre-treatment consisting of a 30-minute soak in 1% (m/v) Bavistin, while the control group was soaked in tap water. Aspergillus flavus and Rhizopus stolonifer infections emerged in the control group. A Mann-Whitney U test showed the control group as having significantly higher infections with both fungi (range of p values = 0.003 to 0.010) during and after germination than the fungicide-treated group. Post-germination seedling survival was also significantly enhanced by 31.66% in the treated group relative to the control (range of p values = 0.004 to 0.010). A single pre-treatment with the systemic fungicide Bavistin may be recommended for reduction of seedling mortality in M. volkensii during and after germination