Assessment of soil health using nematode assemblage and soil characteristics in vertisols, cambisols and arenosols of Kenya

Abstract

Maintenance of soil health (biological, physiochemical, nutritional and water holding integrity) is critical to meeting Kenya's food security and adaptation to climate change. Soil health assessment however has been based on single parameters which ignore multiple and interacting biological processes that are the basis to sustainable crop productivity. As part of a continental project aiming at assessing and developing scalable soil health management strategies, this study was based on Arenosol, Cambisol and Vertisol soil groups in Kenya. This study was carried out to develop accurate scalable soil-health models using soil groups that address soil degradations in Kenya. To achieve this goal, the potential of using seasonal variations in nematode assemblages in different soil groups as an indicator of soil health was assessed. Three approaches were utilized to achieve a comprehensive dataset on the status of soil degradations in the soil group models in the study. First, 576 soil cores of lkg were sampled in areas characterized by small scale subsistence agriculture in Murang'a county (northern sites) and Machakos & Makueni counties (southern sites) during three different seasons. The sampling points included land under cultivation (disturbed) and the adjoining natural (undisturbed) sites within three soil groups, namely; Vertisols, Cambisols and Arenosols. Nematodes were extracted using the sugar density centrifugation technique, enumerated and assigned to their respective trophic groups. Secondly, soil chemical and physical analyses were also carried out in the same 576 soil cores to determine how the relationships between the different soil parameters and nematode communities are influenced by different seasons, soil groups, sites and disturbance with regard to the nematode soil food web, ecological disturbance and nutrient cycling. Finally, a survey involving interviews of 150 farmers was carried out in the Northern and Southern regions within farms located in the three soil groups to determine the land use and socio-economic activities that may have influenced variation in degradations in the two regions. Nematode abundance varied significantly across the seasons with an increase being recorded from season one to two and a decrease in season three. The nematode abundance and abundance was higher in the natural sites, in the northern sites, in the Cambisols and it increased in the warm/rainy season. Correlation analysis revealed that the different nematode feeding groups associated variably with the soil chemical properties. Asseessment of ecological disturbance revealed that moist and natural conditions are important in improving the maturity index (MI). An analysis of the soil food web revealed that the basal (BI) and structural (SI) indices were similar across the soil groups while enrichment index (El) was significantly higher in Vertisols and Cambisols xiv compared to the Arenosols. In addition, seasons and landscapes had a significant effect on BI, El and SI. The survey of 150 farms revealed that variable activities with regard to durations of crop cultivation, amendment application, rotation and tillage strategies in the Northern and Southern regions .may have an effect on soil health and degradations. This study has demonstrated that nematode communities occur differently due to seasonal changes and soil groups making them viable bio-indicators of soil health. In addition, it was realized that changes in soil properties, resulting from anthropogenic activities, have a significant effect on nematode assemblages in their respective food webs. Adoption of sustainable land use strategies to enhance soil health and structure and promote crop productivity is recommended.