From Contamination to Functional Shift: Agrochemical Effects on Soil Microbial C:N:P Balance and Enzymatic Activity

Abstract

Background: Agrochemicals, while vital for enhancing agricultural productivity, are increasingly recognized as environmental pollutants, impacting soil health and microbial ecosystems. Aim: This study examined the microbial biomass carbon (MB-C), nitrogen (MB-N), phosphorus (MB-P), soil enzyme activities, and phospholipid fatty acid (PLFA) composition of an agrochemical-contaminated farm soil in Ogume, Kwale, Delta State, Nigeria. Methodology: Soil samples were collected from a farm with a history of intensive agrochemical application and a control site. Microbial biomass carbon (MB-C), nitrogen (MB-N), phosphorus (MB-P), soil enzyme activities, phospholipid fatty acids (PLFAs) and polycyclic aromatic hydrocarbons (PAHs) were determined using standard procedures. Results: Results revealed that microbial biomass C, N, and P were significantly lower in contaminated soil (17.86mg/kg, 312.06 mg/kg, and 87.14 mg/kg) compared to the control (15.8mg/kg, 523.47 mg/kg, and 205.32 mg/kg). Similarly, enzyme activities were reduced in the contaminated soil; with β-glucosidase (0.562 µg PNP kg⁻¹ h⁻¹), urease (0.56 mg N NH₄ kg⁻¹ h⁻¹), and phosphatase (25.46 mg PNP kg⁻¹ h⁻¹) values lower than those in the control (0.680 µg PNP kg⁻¹ h⁻¹, 0.63 mg N NH₄ kg⁻¹ h⁻¹, and 29.80 mg PNP kg⁻¹ h⁻¹). Dehydrogenase activity was marginally higher in contaminated soil (6.80 µg PNP kg⁻¹ h⁻¹) than in control soil (6.44 µg PNP kg⁻¹ h⁻¹), suggesting microbial stress adaptation. The total phospholipid fatty acid (PLFA) content in the contaminated soil (10.24 µmol g⁻¹) was notably lower than that of the control (12.46 µmol g⁻¹), reflecting a reduction in viable microbial biomass and potential shifts in community structure associated with agrochemical exposure. No detectable PAHs in both soil samples, implying that microbial and enzymatic alterations were primarily due to agrochemical residues rather than pyrogenic pollution. Conclusion: This investigation contributes to a better understanding of the ecological consequences of agrochemical pollution on soil microbial communities in tropical agricultural settings, offering valuable insights for sustainable land management and bioremediation strategies.