School of Agriculture and Biotechnology
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Item Bioecology of thrips in French bean growing: agroecosystems in Kenya.(1999) Gitonga, Gitonga, Linus MuthuriStudies on the bioecology ofthrips on French beans were carried out at Machakos, Kaguru and JKUAT. The general objectives of this study were twofold, namely to study the biology and population dynamics of thrips on French beans and to identify and evaluate indigenous natural enemies of the thrips. Two thrips species, M sjostedti and F occidentalis were found throughout the year on French bean crops in all localities of the study. Their population peaks occurred at different times in the course of the year. Populations of M sjostedti peaked after the rains while those of F occidentalis occurred during the hot and dry months of the year at all the localities. Studies on the movements of thrips, into and out of the French bean crops showed that colonization by both species begins soon after germination and that both species preferred the flowers to other plant parts. F occidentalis was found to thrive equally well on the leaves, unlike M sjostedti which only inhabited flower buds and flowers. During the pre-flowering phase ofthe crop, M sjostedti were found on the terminal buds from where they moved to the flowers immediately after the onset of flowering. Most first instar larvae emerged from the pods and flowers. Petioles, leaves, flower buds, flowers and pods were used as oviposition substrates by the thrips.to varying extents. Analysis of the spatial distribution showed both species to be significantly aggregated in the respective plant parts. Laboratory studies indicated that developmental period decreased with an increase in temperature for all the stages of M sjostedti and F. occidentalis. Developmental threshold temperatures were calculated as 9.6 and 9.0 for M sjostedti and F. occidentalis respectively. Development from egg to adult required 212.0 and 256.8 Degree Days for M sjostedti and F. occidentalis respectively. However, at 15?C and 300C, mortality rates for all the developmental stages were higher for M sjostedti than F. occidentalis. The highest mortalities were recorded for the first instar larvae for both species, ranging from 15% to 42% and 11 % to 30% for M sjostedti and F. occidentalis respectively. Pre-pupae and pupae had the lowest mortality rates. An indigenous anthocorid bug, Orius albidipennis was found throughout the year in all the three field sites. Studies on the functional responses of 0. albidipennis to M sjostedti showed that more second instar larvae than adult M sjostedti were killed at all the temperature profiles and densities. With increase in temperature, more second instar larvae and adult M sjostedti were killed. High f2 values shows that both Types I and IT functional responses provided good fit for the data at 15?C, 25?C and 28?C. Attack rates also increased with an increase in temperature. Mortality rates of the 0. albidipennis nymphal instars decreased from the first to the 5th instar at all the temperatures. The mortality rates at 25?C were lower than at 20?C and 30?C for all the nymphal instars except the first instar. Temperatures had a significant effect on the pre-oviposition period, which decreased with an increase in temperature. The eggs took long to hatch at 20?C. Developmental periods of each of the nymphal instars decreased with an increase in temperature. An indigenous larval endoparasitoid of thrips, Ceranisus menes, was found throughout the year in the three localities and its population peaks occurred in the late and early months of the year, from October to April. A closer correlation was found between C. menes and F. occidentalis than with M sjostedti. At JKUAT, percentage parasitism, over the entire crop cycle, ranged from 3.5% to 19.5% and peaked in the months of Marchi April. The lowest percentage parasitism coincided with the period of the highest M sjostedti infestation on French beans. Linear regression analysis showed a density dependence relationship between parasitism and larval density. Laboratory experiments showed that C. menes successfully parasitized and completed development in both M sjostedti and F. occidentalis. Developmental times of C. menes in M sjostedti and F. occidentalis were not significantly different.Item EVALUATION OF THE EFFECTS OF CONSERVATION AGRICULTURE ON SOIL PROPERTIES IN LAIKIPIA COUNTY, KENYA(Karatina University, 2023-11) KINYUMU, DANIEL MWANGANGIConservation agriculture (CA), defined by three principles of; minimum soil disturbance, use of cover crop and crop rotation/diversification was introduced in Laikipia as alternative to conventional farming (CF) systems, to improve soil properties and resilience to climate change and soil degradation. The study investigated practice of CA by farmers and carried out in-situ and laboratory analysis of soil moisture, bulk density, texture, soil nitrogen, phosphorus, exchangeable cations and microbial diversity. The study area was purposively selected to include areas where CA had historically been practised. A population of 2,000 farmers registered as practising CA were interviewed. For the collection of soil samples, 332 farmers were sampled based on; (i) farmers who received training on CA curriculum (ii) farmers who were actively practising all the three principles of CA (minimum soil disturbance, crop rotation and soil cover); and (iii) farmers who were practising CA alongside conventional farming. Thirty (30) farmers were sampled according population in each through proportionate stratified random sampling. 270 composite soil samples were collected from 3x3 m plots at a depth of 0-20 cm (rooting zone) of annual crops, from 30 farms, during 2019 and 2020 cropping seasons. Soil sampling for analysis soil bulk density, moisture) while soil sampling for the analysis of chemical and microbial properties was done using core ring sampler of 5cm diameter and 10cm height and metallic soil augers of 5cm diameter, respectively. The analysis of soil physical and chemical properties were done according to protocols in soil and plant analysis and national agricultural research laboratories (NARL) manuals. The analysis of microbial diversity was done according to functional gene analysis pipeline (www.mrdnalab.com). Findings describing significance differences in soil properties between farming systems were done using one-way analysis of variance (ANOVA) at (p ≤ 0.05), followed by post-hoc family-wise comparisons of means between experimental plots. Tukey’s honest significance difference (HSD) tested mean separation when analysis showed statistically significant differences (p < 0.05). The DNA from environmental samples was extracted using PureLinkTM Microbiome DNA Purification Kit (Thermo Fisher Scientific). Amplicon generation and sequencing was done using the next generation (NGS) Illumina’s MiSeq technology platform (bTEFAP)®. All statistical analyses were performed using IBM SPSS ver 22, R-program and MS-Excel for Windows. Findings of CA farming practices indicated that 67% of farmers employed all the three principles of conservation agriculture (crop cover/residue + crop rotation + no tillage). Majority (62%) of farmers were largely subsistence farmers, growing mainly; maize (Zea mays L.) and beans (Phaseolus vulgaris L.). Silt clay loam (SCL) was the most abundant at 60%, while 67.47% of farmers employed all the 3 principles of CA. Farms adopting CA had the highest soil bulk density at 1.78 ±0.04 g/cm3. Soil moisture levels in farms declined significantly from ‘25” to “75” days after seeding (DAS) under different farming systems. Soil carbon was significantly higher in farms adopting CA, which is postulated to be due to the high use of organic biomass on soil. The study found important rhizospheric bacteria and fungi that affects soil properties. The findings can be used for developing a holistic soil improvement strategy for improving soil properties and enhancing farmer resilience to climate change effects in rain-fed farming systems in Laikipia.Collection Collection