Soil Acidification is Associated with Plant-Parasitic Nematode Dominance and Ecosystem Degradation in Kenyan Sugarcane

Sugarcane (Saccharum officinarum) is a crucial cash crop in Kenya's western sugar belt, yet its productivity is constrained by interrelated soil chemical deficiencies and soil-borne pests. This study examined nematode-community dynamics and soil physicochemical properties across five representative smallholder sugarcane farms (Farms A–E) in the Sangalo area of Nandi County. Soil assessment indicated marked chemical stress, characterised by high acidity (pH = 4.88) and depleted macronutrients (total nitrogen = 0.4%, available phosphorus = 6.5 ppm, and exchangeable potassium = 0.56 meq/100 g). Nematode communities were dominated by plant-parasitic nematodes, particularly Helicotylenchus spp. and Pratylenchus spp. Farm E had the highest Helicotylenchus spp. density, at 2,900 individuals per 100 g of soil. Ecological assessment using the Shannon–Wiener Diversity Index (H′) and Plant Parasitic Index indicated variation in community structure among farms. Farm B had the highest diversity (H′ = 1.58), whereas Farm E had the lowest (H′ = 1.05). Pearson correlation analysis showed negative associations between soil pH and Helicotylenchus abundance (r = −0.94, P = 0.017) and between Helicotylenchus density and community diversity (r = −0.996, P < 0.001). These findings indicate that acidic, nutrient-depleted soils were associated with greater plant-parasitic nematode dominance and reduced nematode-community diversity. Integrated soil-health management, including liming, balanced nutrient application, organic amendments, and appropriate nematode-management practices, may help improve soil conditions and restore trophic balance.