Soil nematode communities as influenced by fertility management practices, growth and yield of common beans (Var. Mwitemania) in Tharaka Nithi, Kenya

Abstract

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