Soil Science

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    Soil nematode communities as influenced by fertility management practices, growth and yield of common beans (Var. Mwitemania) in Tharaka Nithi, Kenya
    (Chuka University, 2025-10) Muraki, Margaret Wairimu
    Common bean yield is relatively low due to soil infertility, diseases, and pests such as plant-parasitic nematodes (PPNs), as well as unfavorable climatic conditions, among other factors. PPNs have been reported to cause yield losses of up to 60% while free living nematodes (FLN) contribute positively to soil health. The study's general objective was to evaluate the effect of fertility management practices on soil nematode communities and the yield of common beans in Tharaka Nithi County. The treatments included NPK (23.23.0), Trichoderma harzianum (45g/20 litres), farmyard manure (10 ton/ha), and a control (with no amendment), which were laid out in a randomized complete block design (RCBD) and replicated three times. Soil samples were taken from the field before bean sowing, at flowering, and after harvesting common beans in each trial. Nematodes were extracted from 200ml of soil and 5g of roots using Modified Baermann technique. Data were collected on bean growth every two weeks and on yield components. Meanwhile, nematode numbers were counted,and species diversity and evenness were calculated per plot. The data values obtained were subjected to analysis of variance using R version 4.5.0, and significant means were separated using the Least Significant Difference Test at α = 0.05. Results showed that in both trials, Farmyard manure increased FLN in soil (941) and showed a significant difference (p<0.05) from all other treatments and compared to the control, which reduced FLN in soil (110). The control treatment had the highest population of PPNs in soil (773) and showed a significant difference (p < 0.05) from the other treatments, while Trichoderma harzianum reduced the PPN population (123) in the soil. Control treatment increased Shannon diversity (1.68), Simpson’s diversity (0.78), and evenness (0.9) of PPNs as compared to Trichoderma harzianum, which reduced Shannon diversity (1.03), Simpson’s diversity (0.49), and evenness (0.85). Trichoderma harzianum increased the Shannon diversity (1.35), Simpson’s diversity (0.7), and evenness (0.84) of FLN compared to the control, which reduced the Shannon diversity (0.85), Simpson’s diversity (0.54), and evenness (0.77). The NPK (23.23.0) treatment had the highest growth response which recorded the highest values across four intervals of data collection on height (85.80 cm), number of leaves (72.5), branches (23.54), pods (25.34) seeds (169.39), biomass (1211.72 kg/ha), and grain yield (4592.60 kg/ha), and showed significant difference (p<0.05) from other treatments while control had the reduced growth response of height (39.08 cm), number of leaves(19.25), branches (5.75), pods (5.87) seeds (32.67), biomass (193.24 kg/ha), and grain yield (586.42 kg/ha). Trichoderma harzianum had the highest number of nodules (50.5) and showed a significant difference from other treatments,while NPK (23.23.0) had the least (2.9). The NPK treatment increased PPNs in roots (46) and showed a significant difference (p < 0.05) from other treatments compared to Trichoderma harzianum, which reduced PPNs (2.5) in roots. Farmyard manure and Trichoderma harzianum emerged as promising strategies for managing PPNs while promoting beneficial nematodes to enhance common bean yields and soil health. Continuous assessment of nematode communities over multiple growing seasons is crucial for understanding the long-term effects of various soil amendments on diversity and crop productivity
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    DYNAMICS OF RHIZOBIUM AND PHOSPHATE ROCK FERTILIZER APPLICATION ON SOIL CHEMICAL PROPERTIES AND PERFORMANCE OF GREEN-GRAMS IN THARAKA - NITHI COUNTY, KENYA
    (Chuka University, 2020-12) MBAKA, FELISTER KEMUNTO
    Soil fertility decline is one of the major constraints in agricultural productivity in Africa. Biological nitrogen fixation (BNF) in green - grams can offer a cost effective and sustainable means towards soil fertility management. Green-gram, a drought tolerant legume, constitutes an important grain legume crop in semi-arid areas of sub Saharan Africa. In Kenya, green-gram is a major source of food security particularly in Tharaka Nithi County. However, green-gram yields are usually low due to low phosphorous and nitrogen levels of the soil. There is limited information on the enhancement of nitrogen fixation efficiency of green - grams through Rhizobium inoculation and phosphate rock among farmers’ preferred green-gram varieties (N26 - nylon and KS20 - uncle). Therefore, the aim of this study was to determine the effect of Rhizobium inoculation and phosphate rock fertilizer on green-grams performance and soil chemical variables. The study was carried out at Chuka university horticultural research farm for two cultivations; November 2019 - January 2020 and February - April 2020. A factorial experiment of 2 x 2 x 2 was laid out in a randomized complete block design. There were three factors, varieties (26 - nylon and KS20 -uncle), phosphate rock (0 and 30 kg P ha-1) and Rhizobium MEA 716 (0 and 100 g ha-1) making a total of eight treatments which were replicated three times. Soil sampling and analyses were done for soil pH, fixed – N and total nitrogen (TN), available Phosphorous, total organic carbon (TOC), fixed – N and potassium before planting and after harvesting of green-grams. Data on growth and yield variables were collected fortnightly on four randomly selected plants on plant height, number of leaves branches, pods, nodules, effective nodules, nodule dry weight, grain yield, total dry biomass, shoot and root dry weights. Nutrient uptake was done for N and P also phosphorus use efficiency (PUE) and nitrogen use efficiency (NUE) were done. Data was analysed using Statistical Analysis Software (SAS). Significant means were separated using Least Significant Difference (LSD) at probability level of 5 %. Results for both cultivations indicated that treatment R1P1V2 showed significantly (P<0.05) higher increase in soil pH (7.54), TN (0.58%), TOC (3.45%), P (68.20 ppm), EC (0.95 Cmolkg-1), K (1.75 Cmolkg-1) and fixed-N (0.50%) over other treatments. Similarly treatment R1P1V2 had significant (P<0.05) increase in number of nodules (101.78 plant-1), effective nodules (9.92 plant-1) and nodule dry weight (3.81g plant-1), these trends were observed in N and P use efficiency and their uptake compared to other treatments. On growth variables treatment R1P1V2 recorded significantly (P<0.05) higher plant height (76.07 cm), number of branches (14.08 plant-1), shoot dry biomass (52.01 g plant-1), root dry biomass (7.60 g plant-1), total dry biomass (146.4 g plant-1), number of pods (84 plant-1) and yield (2158 kg ha-1). Therefore, combination of Rhizobium MEA 716 100 g ha-1 with phosphate rock 30 Kg ha-1 in variety KS20 improved soil chemical properties, enhanced nitrogen fixation ability and equally growth and yield of green-grams. Based on the findings, combining Rhizobium MEA716 100 g ha-1, and 30 Kg ha -1 phosphate rock with variety KS20 was recommended for a sustainable green-gram production and soil fertility management in Chuka area - Tharaka Nithi County.